@article{khokhar2026,
	title = {Thrust {Regulation} in a {Supersonic} {Ducted} {Propulsion} {System} {Using} {CFD}-{Coupled} {Adaptive} {Control}},
	journal = {Journal of Spacecraft and Rockets (under review)},
	author = {Khokhar, Gohar T. and Hanquist, Kyle M. and Oveissi, Parham and Dorsey, Alex and Goel, Ankit},
	year = {2026},
	keywords = {own},
}

@article{liza2026,
	title = {Numerical {Investigation} of {Nonequilibrium} {Effects} on {Aero}-{Optics} in {Hypersonic} {Flows}},
	journal = {Journal of Thermophysics and Heat Transfer},
	author = {Liza, Martin E. and Hanquist, Kyle M.},
	year = {2026},
	keywords = {own},
}

@article{larsen2026,
	title = {Multi-{Fidelity} {Theory} and {Simulation} of {High}-{Enthalpy} {Shock} {Tubes}},
	journal = {Shock Waves (under review)},
	author = {Larsen, Aaron and Hanquist, Kyle M.},
	year = {2026},
	keywords = {own},
}

@article{tumuklu2024,
	title = {Hypersonic turbulence wake modeling from rarefied to continuum regimes},
	volume = {2996},
	doi = {10.1063/5.0187575},
	abstract = {Hypersonic flows over a cylinder are studied to investigate the unsteady characteristics of rarefied and continuum turbulent wake flows. To do this end, an open-source DSMC solver, SPARTA, is used to capture large gradients associated with shock expansion waves separation region interactions especially in the wake region. Conversely, continuum simulations are carried out using an open-source continuum non-equilibrium solver, SU2-NEMO, for relatively low-pressure rarefied nature of flows with a freestream pressure of up to 100 Pa. Comparisons were made using SPARTA and SU2-NEMO at moderately low freestream pressures of 100 Pa for NS and very good agreement is achieved using continuum and rarefied solvers, indicating that DSMC and continuum numerical parameters are accurately selected. Numerical probes are inserted at various locations to study the temporal and turbulence characteristics by performing ensemble averaging each time step of DSMC. Consistent with previous numerical studies, x-velocity, y-velocity, and cross-velocity fluctuations are mostly dominant in the wake, bow, and tail shock region. For higher pressure cases, temporal characteristics of residuals are reported to calculate the frequency of oscillations seen in the wake with various Reynolds numbers (Re). The frequency of oscillations is found to be in relatively good agreement with previous experimental measurements and tends to increase with Re.},
	language = {en},
	number = {1},
	journal = {AIP Conference Proceedings},
	author = {Tumuklu, Ozgur and Hanquist, Kyle M.},
	year = {2024},
	keywords = {own},
}

Hypersonic flows over a cylinder are studied to investigate the unsteady characteristics of rarefied and continuum turbulent wake flows. To do this end, an open-source DSMC solver, SPARTA, is used to capture large gradients associated with shock expansion waves separation region interactions especially in the wake region. Conversely, continuum simulations are carried out using an open-source continuum non-equilibrium solver, SU2-NEMO, for relatively low-pressure rarefied nature of flows with a freestream pressure of up to 100 Pa. Comparisons were made using SPARTA and SU2-NEMO at moderately low freestream pressures of 100 Pa for NS and very good agreement is achieved using continuum and rarefied solvers, indicating that DSMC and continuum numerical parameters are accurately selected. Numerical probes are inserted at various locations to study the temporal and turbulence characteristics by performing ensemble averaging each time step of DSMC. Consistent with previous numerical studies, x-velocity, y-velocity, and cross-velocity fluctuations are mostly dominant in the wake, bow, and tail shock region. For higher pressure cases, temporal characteristics of residuals are reported to calculate the frequency of oscillations seen in the wake with various Reynolds numbers (Re). The frequency of oscillations is found to be in relatively good agreement with previous experimental measurements and tends to increase with Re.

@article{tumuklu2023c,
	title = {Temporal characteristics of hypersonic flows over a double wedge with {Reynolds} number},
	volume = {35},
	doi = {10.1063/5.0169648},
	abstract = {Laminar hypersonic flows at Mach 7.10 with unit Reynolds numbers of    5.2 ×   10 4 ,   1.04 ×   10 5, and    4.14 ×   10 5 m−1 over a 30°/55° double-wedge configuration were studied to investigate the spatial–temporal characteristics of the flow in a time-accurate manner. Close comparisons were made between previous kinetic and current continuum approaches to test the validity of the continuum assumption, especially considering the presence of large gradients associated with shock–shock and shock–boundary layer interactions, as well as spanwise instabilities. Previous results from direct simulation Monte Carlo, which inherently predicts rarefied effects such as velocity slip and temperature jumps, were found to be in very close agreement with the current work, even for the lowest Reynolds number. The impact of velocity slip and temperature jumps on flow and surface parameters was investigated, and comparisons were made with a no-slip and constant temperature wall model. The temporal and spatial variation of two- and three-dimensional flows were thoroughly investigated using two-dimensional (2D), three-dimensional (3D) periodic sidewall boundary conditions, and a full 3D configuration consistent with existing experimental data. Close comparisons among the 2D and 3D cases were made. The characteristics of 2D periodic oscillations were reported for the moderate Reynolds number case for the first time. The presence of spanwise instabilities, even at a relatively low free stream pressure of about 100 Pa, establishes that the flow field depends on spanwise effects and is fully 3D. High-fidelity numerical schlieren videos captured strong spanwise oscillations for 3D configurations.},
	number = {10},
	journal = {Physics of Fluids},
	author = {Tumuklu, Ozgur and Hanquist, Kyle M.},
	month = oct,
	year = {2023},
	keywords = {own},
}

Laminar hypersonic flows at Mach 7.10 with unit Reynolds numbers of 5.2 × 10 4 ,   1.04 × 10 5, and 4.14 × 10 5 m−1 over a 30°/55° double-wedge configuration were studied to investigate the spatial–temporal characteristics of the flow in a time-accurate manner. Close comparisons were made between previous kinetic and current continuum approaches to test the validity of the continuum assumption, especially considering the presence of large gradients associated with shock–shock and shock–boundary layer interactions, as well as spanwise instabilities. Previous results from direct simulation Monte Carlo, which inherently predicts rarefied effects such as velocity slip and temperature jumps, were found to be in very close agreement with the current work, even for the lowest Reynolds number. The impact of velocity slip and temperature jumps on flow and surface parameters was investigated, and comparisons were made with a no-slip and constant temperature wall model. The temporal and spatial variation of two- and three-dimensional flows were thoroughly investigated using two-dimensional (2D), three-dimensional (3D) periodic sidewall boundary conditions, and a full 3D configuration consistent with existing experimental data. Close comparisons among the 2D and 3D cases were made. The characteristics of 2D periodic oscillations were reported for the moderate Reynolds number case for the first time. The presence of spanwise instabilities, even at a relatively low free stream pressure of about 100 Pa, establishes that the flow field depends on spanwise effects and is fully 3D. High-fidelity numerical schlieren videos captured strong spanwise oscillations for 3D configurations.

@article{huang2022,
	title = {Study of fluid–thermal–structural interaction in high-temperature high-speed flow using multi-fidelity multi-variate surrogates},
	volume = {113},
	doi = {10.1016/j.jfluidstructs.2022.103682},
	abstract = {This study investigates the impact of the high-temperature effect, especially the real gas effect and chemical reactions, on hypersonic aerothermodynamic solutions of double cone and double wedge configurations, as well as the fluid–thermal–structural interaction of a double wedge configuration in hypersonic flow. First, a high-temperature computational fluid dynamics (CFD) code was benchmarked and correlated with experimental results, emphasizing the impact of high-temperature effects as well as turbulence modeling on heat flux prediction. Subsequently, the multi-fidelity multi-variate Gaussian process regression (M2GPR ) method for problems with high-dimensional outputs was developed to create an aerothermal surrogate model. The model achieves a balance between model accuracy and computational cost of sample generation, using the combination of a few high-fidelity samples and many low-fidelity samples. The numerical examples show that, using the M2GPR formulation, the required number of high-fidelity samples may be reduced by over 80\% while maintaining an accuracy comparable to the high-fidelity CFD solvers. In addition, a geodesic-distance-based metric is developed to inform the choice of high-dimensional datasets of different fidelities for the M2GPR surrogate with improved accuracy. Finally, the aerothermal surrogate was applied to study the impact of the high-temperature effect on the aerothermoelastic response of a hypersonic skin panel, emphasizing the necessity of the accurate characterization of the localized heat flux for reasonable assessment of the response of a compliant structure in high-speed high-temperature flowfield.},
	journal = {Journal of Fluids and Structures},
	author = {Huang, Daning and Sadagopan, Aravinth and Düzel, Ümran and Hanquist, Kyle M.},
	year = {2022},
	keywords = {Grassmannian geodesic distance, High-speed fluid–thermal–structural interaction, High-temperature effects, Hypersonic aerothermodynamics, Multi-fidelity surrogate modeling, Multivariate Gaussian process regression, graduate\_student, own},
}

This study investigates the impact of the high-temperature effect, especially the real gas effect and chemical reactions, on hypersonic aerothermodynamic solutions of double cone and double wedge configurations, as well as the fluid–thermal–structural interaction of a double wedge configuration in hypersonic flow. First, a high-temperature computational fluid dynamics (CFD) code was benchmarked and correlated with experimental results, emphasizing the impact of high-temperature effects as well as turbulence modeling on heat flux prediction. Subsequently, the multi-fidelity multi-variate Gaussian process regression (M2GPR ) method for problems with high-dimensional outputs was developed to create an aerothermal surrogate model. The model achieves a balance between model accuracy and computational cost of sample generation, using the combination of a few high-fidelity samples and many low-fidelity samples. The numerical examples show that, using the M2GPR formulation, the required number of high-fidelity samples may be reduced by over 80% while maintaining an accuracy comparable to the high-fidelity CFD solvers. In addition, a geodesic-distance-based metric is developed to inform the choice of high-dimensional datasets of different fidelities for the M2GPR surrogate with improved accuracy. Finally, the aerothermal surrogate was applied to study the impact of the high-temperature effect on the aerothermoelastic response of a hypersonic skin panel, emphasizing the necessity of the accurate characterization of the localized heat flux for reasonable assessment of the response of a compliant structure in high-speed high-temperature flowfield.

@article{gimelshein2022,
	title = {Kinetic and {Continuum} {Modeling} of {High}-{Temperature} {Air} {Relaxation}},
	doi = {10.2514/1.T6462},
	abstract = {Fully kinetic, vibrationally kinetic, and continuum solvers with varying model fidelity are used in this work to model the high-temperature relaxation of air in 7230 and 15,000 K adiabatic heat bat...},
	journal = {Journal of Thermophysics and Heat Transfer},
	author = {Gimelshein, Sergey F. and Wysong, Ingrid J. and Fangman, Alexander J. and Andrienko, Daniil A. and Kunova, Olga V. and Kustova, Elena V. and Morgado, Fabio and Garbacz, Catarina and Fossati, Marco and Hanquist, Kyle M.},
	year = {2022},
	keywords = {CFD, Chemical Equilibrium, Direct Simulation Monte Carlo, Heat Flux, High Enthalpy Shock Tunnel, Hypersonic Flows, Nonequilibrium Thermochemistry, Nonequilibrium Vibrational Chemical Kinetics, Stagnation Point, Vibrational Energy, own},
	pages = {1--23},
}

Fully kinetic, vibrationally kinetic, and continuum solvers with varying model fidelity are used in this work to model the high-temperature relaxation of air in 7230 and 15,000 K adiabatic heat bat...

@article{gimelshein2022c,
	title = {Kinetic and {Continuum} {Modeling} of {High}-{Temperature} {Oxygen} and {Nitrogen} {Binary} {Mixtures}},
	doi = {10.2514/1.T6258},
	abstract = {The present paper provides a comprehensive comparative analysis of thermochemistry models of various fidelity levels developed in leading research groups around the world. Fully kinetic, hybrid kin...},
	journal = {Journal of Thermophysics and Heat Transfer},
	author = {Gimelshein, Sergey F. and Wysong, Ingrid J. and Fangman, Alexander J. and Andrienko, Daniil A. and Kunova, Olga V. and Kustova, Elena V. and Garbacz, Catarina and Fossati, Marco and Hanquist, Kyle M.},
	year = {2022},
	keywords = {own},
	pages = {1--20},
}

The present paper provides a comprehensive comparative analysis of thermochemistry models of various fidelity levels developed in leading research groups around the world. Fully kinetic, hybrid kin...

@article{parent2021d,
	title = {Plasma {Sheath} {Modelling} for {Computational} {Aerothermodynamics} and {Magnetohydrodynamics}},
	volume = {35},
	doi = {10.1080/10618562.2021.1949456},
	abstract = {To date, plasma sheath effects have not been incorporated into most CFD simulations of magnetohydrodynamics (MHD) or aerothermodynamics due to the high computational costs involved. The accurate mo...},
	number = {5},
	journal = {International Journal of Computational Fluid Dynamics},
	author = {Parent, Bernard and Hanquist, Kyle M.},
	year = {2021},
	keywords = {Plasma sheath, electron transpiration cooling, hypersonic flight, magnetohydrodynamics, own, re-entry flows},
	pages = {331--348},
}

To date, plasma sheath effects have not been incorporated into most CFD simulations of magnetohydrodynamics (MHD) or aerothermodynamics due to the high computational costs involved. The accurate mo...

@article{campbell2021,
	title = {Evaluation of {Computational} {Models} for {Electron} {Transpiration} {Cooling}},
	volume = {8},
	doi = {10.3390/AEROSPACE8090243},
	abstract = {Recent developments in the world of hypersonic flight have brought increased attention to the thermal response of materials exposed to high-enthalpy gases. One promising concept is electron transpiration cooling (ETC) that provides the prospect of a passive heat removal mechanism, rivaling and possibly outperforming that of radiative cooling. In this work, non-equilibrium CFD simulations are performed to evaluate the possible roles of this cooling mode under high-enthalpy conditions obtainable in plasma torch ground-test facilities capable of long flow times. The work focuses on the test case of argon gas being heated to achieve enthalpies equivalent to post-shock conditions experienced by a vehicle flying through the atmosphere at hypersonic speed. Simulations are performed at a range of conditions and are used to calibrate direct comparisons between torch operating conditions and resulting flow properties. These comparisons highlight important modeling considerations for simulating long-duration, hot chamber tests. Simulation results correspond well with the experimental measurements of gas temperature, material surface temperature as well as measured current generated in the test article. Theoretical methods taking into consideration space charge limitations are presented and applied to provide design suggestions to boost the ETC effect in future experiments.},
	number = {9},
	journal = {Aerospace},
	author = {Campbell, Nicholas S. and Hanquist, Kyle M. and Morin, Andrew and Meyers, Jason and Boyd, Iain},
	year = {2021},
	keywords = {equilibrium gas dynamics, gas, hypersonic flight, non, own, plasma and ionized flows, surface interaction},
}

Recent developments in the world of hypersonic flight have brought increased attention to the thermal response of materials exposed to high-enthalpy gases. One promising concept is electron transpiration cooling (ETC) that provides the prospect of a passive heat removal mechanism, rivaling and possibly outperforming that of radiative cooling. In this work, non-equilibrium CFD simulations are performed to evaluate the possible roles of this cooling mode under high-enthalpy conditions obtainable in plasma torch ground-test facilities capable of long flow times. The work focuses on the test case of argon gas being heated to achieve enthalpies equivalent to post-shock conditions experienced by a vehicle flying through the atmosphere at hypersonic speed. Simulations are performed at a range of conditions and are used to calibrate direct comparisons between torch operating conditions and resulting flow properties. These comparisons highlight important modeling considerations for simulating long-duration, hot chamber tests. Simulation results correspond well with the experimental measurements of gas temperature, material surface temperature as well as measured current generated in the test article. Theoretical methods taking into consideration space charge limitations are presented and applied to provide design suggestions to boost the ETC effect in future experiments.

@article{streicher2020,
	title = {Shock-tube measurements of coupled vibration-dissociation time-histories and rate parameters in oxygen and argon mixtures from 5000 {K} to 10 000 {K}},
	volume = {32},
	doi = {10.1063/5.0012426},
	abstract = {Shock-tube experiments were conducted behind reflected shocks using ultraviolet (UV) laser absorption to measure coupled vibration-dissociation (CVDV) time-histories and rate parameters in dilute mixtures of oxygen (O2) and argon (Ar). Experiments probed 2\% and 5\% O2 in Ar mixtures for initial post-reflected-shock conditions from 5000 K to 10 000 K and 0.04 atm to 0.45 atm. A tunable, pulsed UV laser absorption diagnostic measured absorbance time-histories from the fourth, fifth, and sixth vibrational levels of the electronic ground state of O2, and experiments were repeated - with closely matched temperature and pressure conditions - to probe absorbance time-histories corresponding to each vibrational level. The absorbance ratio from two vibrational levels, interpreted via an experimentally validated spectroscopic model, determined vibrational temperature time-histories. In contrast, the absorbance involving a single vibrational level determined vibrational-state-specific number density time-histories. These temperature and state-specific number density time-histories agree reasonably well with state-to-state modeling at low temperatures but deviate significantly at high temperatures. Further analysis of the vibrational temperature and number density time-histories isolated coupling parameters from the Marrone and Treanor CVDV model, including vibrational relaxation time (τ), average vibrational energy loss (ϵ), vibrational coupling factor (Z), and dissociation rate constant (kd). The results for τ and kd are consistent with previous results, exhibit low scatter, and - in the case of vibrational relaxation time - extend measurements to higher temperatures than previous experiments. The results for ϵ and Z overlap some common models, exhibit relatively low scatter, and provide novel experimental data.},
	number = {7},
	journal = {Physics of Fluids},
	author = {Streicher, Jesse W. and Krish, Ajay and Hanson, Ronald K. and Hanquist, Kyle M. and Chaudhry, Ross S. and Boyd, Iain D.},
	year = {2020},
	keywords = {own},
	pages = {1--21},
}

Shock-tube experiments were conducted behind reflected shocks using ultraviolet (UV) laser absorption to measure coupled vibration-dissociation (CVDV) time-histories and rate parameters in dilute mixtures of oxygen (O2) and argon (Ar). Experiments probed 2% and 5% O2 in Ar mixtures for initial post-reflected-shock conditions from 5000 K to 10 000 K and 0.04 atm to 0.45 atm. A tunable, pulsed UV laser absorption diagnostic measured absorbance time-histories from the fourth, fifth, and sixth vibrational levels of the electronic ground state of O2, and experiments were repeated - with closely matched temperature and pressure conditions - to probe absorbance time-histories corresponding to each vibrational level. The absorbance ratio from two vibrational levels, interpreted via an experimentally validated spectroscopic model, determined vibrational temperature time-histories. In contrast, the absorbance involving a single vibrational level determined vibrational-state-specific number density time-histories. These temperature and state-specific number density time-histories agree reasonably well with state-to-state modeling at low temperatures but deviate significantly at high temperatures. Further analysis of the vibrational temperature and number density time-histories isolated coupling parameters from the Marrone and Treanor CVDV model, including vibrational relaxation time (τ), average vibrational energy loss (ϵ), vibrational coupling factor (Z), and dissociation rate constant (kd). The results for τ and kd are consistent with previous results, exhibit low scatter, and - in the case of vibrational relaxation time - extend measurements to higher temperatures than previous experiments. The results for ϵ and Z overlap some common models, exhibit relatively low scatter, and provide novel experimental data.

@article{holloway2020a,
	title = {Assessment of {Thermochemistry} {Modeling} for {Hypersonic} {Flow} over a {Double} {Cone}},
	volume = {34},
	doi = {10.2514/1.T5792},
	abstract = {The influence of different assumptions for thermochemistry modeling in hypersonic flow over a double-cone geometry is investigated. A computational fluid dynamics analysis is used to study the double cone in three different thermochemical cases, nonequilibrium flow, equilibrium flow, and frozen flow, for four different mixtures of nitrogen and oxygen. Specific areas of interest include the thermochemistry model effects on the flowfield and surface properties. The resulting aerodynamic loads are compared with experiments and indicate that thermochemistry modeling assumptions play a significant role in determining surface properties. It is also shown that heat loading is more sensitive to thermochemical modeling than drag and suggests that an accurate measurement of surface heat transfer is of particular interest. Careful analysis also reveals that high-enthalpy and pure oxygen flows are particularly sensitive to the thermochemistry model assumed. Consistent overprediction or underprediction of pressure drag and heat load by all three chemistry models for most of the cases considered indicates a fundamental difference between the actual experiments and the simulations, thus limiting the usefulness of the double-cone data for validation of thermochemistry models.},
	number = {3},
	journal = {Journal of Thermophysics and Heat Transfer},
	author = {Holloway, Michael E. and Hanquist, Kyle M. and Boyd, Iain D.},
	year = {2020},
	keywords = {own},
	pages = {538--547},
}

The influence of different assumptions for thermochemistry modeling in hypersonic flow over a double-cone geometry is investigated. A computational fluid dynamics analysis is used to study the double cone in three different thermochemical cases, nonequilibrium flow, equilibrium flow, and frozen flow, for four different mixtures of nitrogen and oxygen. Specific areas of interest include the thermochemistry model effects on the flowfield and surface properties. The resulting aerodynamic loads are compared with experiments and indicate that thermochemistry modeling assumptions play a significant role in determining surface properties. It is also shown that heat loading is more sensitive to thermochemical modeling than drag and suggests that an accurate measurement of surface heat transfer is of particular interest. Careful analysis also reveals that high-enthalpy and pure oxygen flows are particularly sensitive to the thermochemistry model assumed. Consistent overprediction or underprediction of pressure drag and heat load by all three chemistry models for most of the cases considered indicates a fundamental difference between the actual experiments and the simulations, thus limiting the usefulness of the double-cone data for validation of thermochemistry models.

@article{eyi2019d,
	title = {Shape {Optimization} of {Reentry} {Vehicles} to {Minimize} {Heat} {Loading}},
	volume = {33},
	doi = {10.2514/1.T5705},
	abstract = {The objective of the current study is to designanoptimumreentry vehicle shape thatminimizes heat loading subject to constraints on themaximumvalues of surface heat flux and temperature. A new heat loading formulation is developed for objective function evaluations. Axisymmetric Navier-Stokes and finite-rate chemical reaction equations are solved to evaluate the objectiveandconstraint functions.TheMenterSSTturbulencemodel isemployedfor turbulence closure. A gradient-based method is used for optimization. The sensitivities of the objective and constraint functions are evaluated using the finite-difference method. In shape optimization, the geometry change or the geometry itself is parameterized using different numbers of nonuniform rational basis spline (NURBS) or Bezier curves. Designs are performed at different trajectory points of the IRV-2 vehicle. The effects of flight path angle and reentry velocity on the heat transfer and trajectory characteristics of the original and designed geometries are quantified.},
	number = {3},
	journal = {Journal of Thermophysics and Heat Transfer},
	author = {Eyi, Sinan and Hanquist, Kyle M. and Boyd, Iain D.},
	year = {2019},
	keywords = {own},
	pages = {785--796},
}

The objective of the current study is to designanoptimumreentry vehicle shape thatminimizes heat loading subject to constraints on themaximumvalues of surface heat flux and temperature. A new heat loading formulation is developed for objective function evaluations. Axisymmetric Navier-Stokes and finite-rate chemical reaction equations are solved to evaluate the objectiveandconstraint functions.TheMenterSSTturbulencemodel isemployedfor turbulence closure. A gradient-based method is used for optimization. The sensitivities of the objective and constraint functions are evaluated using the finite-difference method. In shape optimization, the geometry change or the geometry itself is parameterized using different numbers of nonuniform rational basis spline (NURBS) or Bezier curves. Designs are performed at different trajectory points of the IRV-2 vehicle. The effects of flight path angle and reentry velocity on the heat transfer and trajectory characteristics of the original and designed geometries are quantified.

@article{hanquist2019c,
	title = {Plasma {Assisted} {Cooling} of {Hot} {Surfaces} on {Hypersonic} {Vehicles}},
	volume = {7},
	doi = {10.3389/fphy.2019.00009},
	abstract = {Electron transpiration cooling (ETC) is a proposed thermal management approach for the leading edges of hypersonic vehicles that utilizes thermionic emission to emit electrons to carry heat away from the surface. A modeling approach is presented for assessing ETC in a computational fluid dynamics (CFD) framework and is evaluated using previously completed experiments. The modeling approach presented includes developing boundary conditions to account for space-charge-limited emission to accurately determine the level of electron emission from the surface. The effectiveness of ETC for multiple test cases are investigated including sharp leading edges and blunt bodies. For each of these test cases, ETC affects the surface properties, most notably the surface temperature, suggesting that ETC occurs for bodies in thermally intense, ionized flows, no matter the shape of the leading edge. An approximate approach is also presented to assess ETC in an ionized flow and compares its cooling power to radiative cooling.},
	number = {9},
	journal = {Frontiers in Physics: Plasma for Aerospace},
	author = {Hanquist, Kyle M. and Boyd, Iain D.},
	year = {2019},
	keywords = {Computational fluid dynamics, Electron transpiration cooling, Hypersonics, Plasma sheath, Thermionic emission, etc, own},
	pages = {1--13},
}

Electron transpiration cooling (ETC) is a proposed thermal management approach for the leading edges of hypersonic vehicles that utilizes thermionic emission to emit electrons to carry heat away from the surface. A modeling approach is presented for assessing ETC in a computational fluid dynamics (CFD) framework and is evaluated using previously completed experiments. The modeling approach presented includes developing boundary conditions to account for space-charge-limited emission to accurately determine the level of electron emission from the surface. The effectiveness of ETC for multiple test cases are investigated including sharp leading edges and blunt bodies. For each of these test cases, ETC affects the surface properties, most notably the surface temperature, suggesting that ETC occurs for bodies in thermally intense, ionized flows, no matter the shape of the leading edge. An approximate approach is also presented to assess ETC in an ionized flow and compares its cooling power to radiative cooling.

@article{eyi2019b,
	title = {Aerothermodynamic {Design} {Optimization} of {Hypersonic} {Vehicles}},
	volume = {33},
	doi = {10.2514/1.T5523},
	abstract = {The objective of this study is to develop a reliable and efficient design optimization method for hypersonic vehicles focused on aerothermodynamic environments. Considering the nature of hypersonic flight, a high-fidelity aerothermodynamic analysis code is used for the simulation of weakly ionized hypersonic flows in thermochemical nonequilibrium. A gradient-based method is implemented for optimization. Bezier or nonuniform rational basis spline curves are used to parametrize the geometry or the geometry change. Linear elasticity theory is implemented for mesh deformation. Penalty functions are utilized to prevent undesired geometrical changes. The design objective is to minimize drag without increasing the total heat transfer rate and the maximum values of the surface heat flux, temperature, and pressure. Design optimizations are performed at different trajectory points of the IRV-2 vehicle. The effects of parametrizations, the number of design variables, and freestream conditions on design performance are studied.},
	number = {2},
	journal = {Journal of Thermophysics and Heat Transfer},
	author = {Eyi, Sinan and Hanquist, Kyle M. and Boyd, Iain D.},
	year = {2019},
	keywords = {own},
	pages = {392--406},
}

The objective of this study is to develop a reliable and efficient design optimization method for hypersonic vehicles focused on aerothermodynamic environments. Considering the nature of hypersonic flight, a high-fidelity aerothermodynamic analysis code is used for the simulation of weakly ionized hypersonic flows in thermochemical nonequilibrium. A gradient-based method is implemented for optimization. Bezier or nonuniform rational basis spline curves are used to parametrize the geometry or the geometry change. Linear elasticity theory is implemented for mesh deformation. Penalty functions are utilized to prevent undesired geometrical changes. The design objective is to minimize drag without increasing the total heat transfer rate and the maximum values of the surface heat flux, temperature, and pressure. Design optimizations are performed at different trajectory points of the IRV-2 vehicle. The effects of parametrizations, the number of design variables, and freestream conditions on design performance are studied.

@article{hara2018,
	title = {Test cases for grid-based direct kinetic modeling of plasma flows},
	volume = {27},
	doi = {10.1088/1361-6595/aac6b9},
	abstract = {Grid-based kinetic models are promising in that the numerical noise inherent in particle-based methods is essentially eliminated. Here, we call such grid-based techniques a direct kinetic (DK) model. Velocity distribution functions are directly obtained by solving kinetic equations, such as the Vlasov equation, in discretized phase space, i.e., both physical and velocity space. In solving the kinetic equations that are hyperbolic partial differential equations, we employ a conservative, positivity-preserving numerical scheme, which is necessary for robust calculations of problems particularly including ionization. Test cases described in this paper include plasma sheaths with electron emission and injection and expansion of neutral atom flow in a two-dimensional configuration. A unifying kinetic theory of space charge limited sheaths for both floating and conducting surfaces is presented. The improved theory is verified using the collisionless DK simulation, particularly for small sheath potentials that particle-based kinetic simulations may struggle due to statistical noise. For benchmarking of the grid-based and particle-based kinetic simulations, hybrid simulations of Hall thruster discharge plasma are performed. While numerical diffusion occurs in the phase space in the DK simulation, ionization oscillations are well resolved since ionization events can be taken into account deterministically at every time step.},
	number = {6},
	journal = {Plasma Sources Science and Technology},
	author = {Hara, Kentaro and Hanquist, Kyle M.},
	year = {2018},
	keywords = {Hall thruster, Kinetic simulation, Vlasov simulation, etc, nonlinear plasma waves, own, plasma instability, plasma sheaths, space charge limited sheath},
}

Grid-based kinetic models are promising in that the numerical noise inherent in particle-based methods is essentially eliminated. Here, we call such grid-based techniques a direct kinetic (DK) model. Velocity distribution functions are directly obtained by solving kinetic equations, such as the Vlasov equation, in discretized phase space, i.e., both physical and velocity space. In solving the kinetic equations that are hyperbolic partial differential equations, we employ a conservative, positivity-preserving numerical scheme, which is necessary for robust calculations of problems particularly including ionization. Test cases described in this paper include plasma sheaths with electron emission and injection and expansion of neutral atom flow in a two-dimensional configuration. A unifying kinetic theory of space charge limited sheaths for both floating and conducting surfaces is presented. The improved theory is verified using the collisionless DK simulation, particularly for small sheath potentials that particle-based kinetic simulations may struggle due to statistical noise. For benchmarking of the grid-based and particle-based kinetic simulations, hybrid simulations of Hall thruster discharge plasma are performed. While numerical diffusion occurs in the phase space in the DK simulation, ionization oscillations are well resolved since ionization events can be taken into account deterministically at every time step.

@article{hanquist2017c,
	title = {Evaluation of {Computational} {Modeling} of {Electron} {Transpiration} {Cooling} at {High} {Enthalpies}},
	volume = {31},
	doi = {10.2514/1.T4932},
	abstract = {Amodeling approach for electron transpiration cooling of high-enthalpy flight is evaluated through comparison to a set of experiments performed in a plasma arc tunnel for air and argon. The comparisons include air and argon flow at high enthalpies (27.9 and 11.6 MJ/kg, respectively), with a Mach number of 2.5 to 3. The conversion of the reported enthalpies and Mach numbers to freestream temperatures and velocities is discussed. The numerical approach is described, including implementation of a thermionic emission boundary condition and an electric field model. Also described is the implementation of a finite-rate chemistry model for argon ionization. Materials with different electron emission properties are also investigated, including graphite and tungsten. The comparisons include two different geometries with different leading-edge radii. The numerical results produce a wide range of emitted current due to the uncertainties in freestream conditions and emissive material properties, but they still agree well with the experimental measurements.},
	number = {2},
	journal = {Journal of Thermophysics and Heat Transfer},
	author = {Hanquist, Kyle M. and Alkandry, Hicham and Boyd, Iain D.},
	year = {2017},
	keywords = {etc, own},
	pages = {283--293},
}

Amodeling approach for electron transpiration cooling of high-enthalpy flight is evaluated through comparison to a set of experiments performed in a plasma arc tunnel for air and argon. The comparisons include air and argon flow at high enthalpies (27.9 and 11.6 MJ/kg, respectively), with a Mach number of 2.5 to 3. The conversion of the reported enthalpies and Mach numbers to freestream temperatures and velocities is discussed. The numerical approach is described, including implementation of a thermionic emission boundary condition and an electric field model. Also described is the implementation of a finite-rate chemistry model for argon ionization. Materials with different electron emission properties are also investigated, including graphite and tungsten. The comparisons include two different geometries with different leading-edge radii. The numerical results produce a wide range of emitted current due to the uncertainties in freestream conditions and emissive material properties, but they still agree well with the experimental measurements.

@article{hanquist2017b,
	title = {Detailed modeling of electron emission for transpiration cooling of hypersonic vehicles},
	volume = {121},
	doi = {10.1063/1.4974961},
	number = {5},
	journal = {Journal of Applied Physics},
	author = {Hanquist, Kyle M. and Hara, Kentaro and Boyd, Iain D.},
	year = {2017},
	keywords = {own},
	pages = {1--13},
}

@article{visbal2012,
	title = {Onset of vortex breakdown above a pitching delta wing},
	volume = {32},
	url = {https://arc.aiaa.org/doi/abs/10.2514/3.12145},
	doi = {10.2514/3.12145},
	abstract = {Computational results are presented for transient vortex breakdown above a delta wing subject to a pitch-andhold maneuver to high angle of attack. The flows are simulated by solving the full three-dimensional Navier- Stokes equations on a moving grid using the implicit Beam-Warming algorithm. An assessment of the effects of numerical resolution and favorable comparison with experimental data suggest the computational approach captures the basic dynamics of the onset and initial stages of transient breakdown. The pressure gradient along the vortex axis is found to play a dominant role in the initiation of breakdown. A description of the three-dimensional instantaneous structure of the flowfield is provided for the first time using critical-point theory. The reversed-flow region in the vortex core is associated with pairs of opposite spiral/saddle critical points. At its onset, the vortex breakdown is fairly axisymmetric; however, as it proceeds upstream and a stronger jump takes place along the axis, asymmetric effects become important and culminate in the formation of a bubble-type breakdown. This bubble structure is open and contains within itself a pair of stagnation points that are diametrically opposed and that rotate in the same sense as the upstream swirling flow. These critical points suggest the existence of azimuthal disturbances in the breakdown region. The bubble sectional topology is also found in agreement with recent experimental measurements. © 1994 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.},
	number = {8},
	journal = {AIAA Journal},
	author = {Visbal, Miguel R.},
	month = may,
	year = {2012},
	keywords = {Angle of Attack, Cambered Delta Wing, Flow Visualization Techniques, Freestream Mach Number, Navier Stokes Equations, Shear Layers, Streamlines Pattern, Taylor Vortex Flow, Velocity Profiles, Vortex Breakdown},
	pages = {1568--1575},
}

Computational results are presented for transient vortex breakdown above a delta wing subject to a pitch-andhold maneuver to high angle of attack. The flows are simulated by solving the full three-dimensional Navier- Stokes equations on a moving grid using the implicit Beam-Warming algorithm. An assessment of the effects of numerical resolution and favorable comparison with experimental data suggest the computational approach captures the basic dynamics of the onset and initial stages of transient breakdown. The pressure gradient along the vortex axis is found to play a dominant role in the initiation of breakdown. A description of the three-dimensional instantaneous structure of the flowfield is provided for the first time using critical-point theory. The reversed-flow region in the vortex core is associated with pairs of opposite spiral/saddle critical points. At its onset, the vortex breakdown is fairly axisymmetric; however, as it proceeds upstream and a stronger jump takes place along the axis, asymmetric effects become important and culminate in the formation of a bubble-type breakdown. This bubble structure is open and contains within itself a pair of stagnation points that are diametrically opposed and that rotate in the same sense as the upstream swirling flow. These critical points suggest the existence of azimuthal disturbances in the breakdown region. The bubble sectional topology is also found in agreement with recent experimental measurements. © 1994 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.