Development and Verification of the Charring Ablating Thermal Protection Implicit System Solver

Amar, Adam J.; Calvert, Nathan D.; Kirk, Benjamin S.

doi:10.2514/6.2011-144

Cited by 46 publications

(28 citation statements)

References 20 publications

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“…Still, all models (including RANS) are able to predict pressures that are within 1% of the peak pressure value. Along the attached boundary layer (gauges [31][32][33][34][35], all models show very similar results and are very close to the experiment, with the exception of gauges 31 and 35, where the gauges appear to be outliers due to the good performance of other surrounding gauges [2].…”

Section: Pressure and Heat Transfer Resultssupporting

confidence: 79%

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Mach 6 Wake Flow Simulations Using a Large-Eddy Simulation/Reynolds-Averaged Navier–Stokes Model

Salazar

Edwards

2014

Journal of Spacecraft and Rockets

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A hybrid large-eddy simulation/Reynolds-averaged Navier-Stokes turbulence model is used to simulate the Mach 6 flow around a scaled model similar to NASA's Orion multipurpose crew vehicle. The results for surface pressure and heat transfer are compared with experimental data from previous base flow experiments conducted at the CalspanUniversity at Buffalo Research Center. Using the highest Reynolds number test case (11 × 10 6 based on capsule diameter), different numerical aspects of the hybrid approach are addressed, such as use of a low-dissipation scheme, a modification to the eddy-viscosity blending function, time-averaging results, filtering computational results, and sensitivity to grid resolution. In addition, results are compared with Reynolds-Averaged Navier-Stokes using Menter's two-equation baseline model and to detached-eddy simulation predictions. By introducing a new modification to the blending from Reynolds-averaged Navier-Stokes to large-eddy simulation within boundary layers, very good agreement with the experiment is obtained in regions where the boundary-layer grid spacing is too coarse for large-eddy simulation. The findings show that the high-fidelity schemes produce results that agree much better with the experimental data than Reynolds-averaged Navier-Stokes methods, which tend to underpredict base pressures and overpredict heat fluxes. The overall accuracy of each scheme is evaluated using a normalized root mean square error in different regions of the flow, and the analysis shows that, in separated regions, the integrated error is over 120% using a Reynolds-averaged Navier-Stokes model, and 30-50% using the higher fidelity schemes. Additionally, the hybrid methodology presented is further validated by considering a lower Reynolds number (6 × 10 6 ), where the flow is nominally transitional, and very accurate heat transfer predictions are also obtained. NomenclatureC M = hybrid large-eddy simulation/Reynolds-averaged Navier-Stokes model constant, 0.06 D = capsule diameter, m d = distance from the nearest wall, m gl out = blending correction function k, k R = turbulence, resolved kinetic energy, m 2 ∕s 2 l inn , l out = inner, outer boundary-layer length scale, m M ∞ = freestream Mach number Re D = Reynolds number based on capsule diameter S = vorticity tensor, 1∕s T wall = wall temperature, K T ∞ = freestream temperature, K t = time, s U ∞ = freestream velocity, m∕s u i = velocity component, m∕ŝũ = resolvable-scale Favre-averaged velocity component, m∕s u = Favre-averaged velocity component, m∕s Γ = large-eddy simulation/Reynolds-averaged NavierStokes blending function Δ = cell volume, m 3 Δ max = maximum grid spacing over the three coordinate directions, m ϵ = turbulent kinetic energy dissipation rate, m 2 ∕s 3 κ = von Kármán constant λ = length scale ratio for blending function μ μ T= molecular, turbulent viscosity, Pa · s ν = kinematic viscosity, m 2 ∕s ν T = kinematic eddy viscosity, m 2 ∕s ν T;SGS = subgrid kinematic eddy viscosity, m 2 ∕s ρ = density, kg∕m 3 ρ ∞ = freestream density...

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Section: Pressure and Heat Transfer Resultssupporting

confidence: 79%

“…The charring ablator response (CHAR) code developed by Amar et al [32] was used. CHAR is a multidimensional thermal material response code used for solving ablating and nonablating TPS problems, as well as direct and indirect heat transfer problems.…”

Section: Time History Comparisonsmentioning

confidence: 99%

Mach 6 Wake Flow Simulations Using a Large-Eddy Simulation/Reynolds-Averaged Navier–Stokes Model

Salazar

Edwards

2014

Journal of Spacecraft and Rockets

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“…In addition, since the gas is eventually blown into the chemical reacting boundary layer [6], correct modeling of the pyrolysis gas is also important to help determine the surface boundary conditions. The gas flow within the charring ablator is often modeled as a porous media flow, for which steady-state Darcy's law is usually assumed [7][8][9][10]. For unsteady charring ablation problems, however, Weng and Martin [4] and Weng et al [5] showed that the steady state of Darcy's law is not necessarily valid for the whole geometry of small test articles used in arc-jet facilities.…”

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confidence: 99%

Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Weng

Martin

2015

Journal of Thermophysics and Heat Transfer

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An orthotropic material model is implemented in a three-dimensional material response code, and numerically studied for charring ablative material. Model comparison is performed using an iso-Q sample geometry. The comparison is presented using pyrolysis gas streamlines and time series of temperature at selected virtual thermocouples. Results show that orthotropic permeability affects both pyrolysis gas flow and thermal response, but orthotropic thermal conductivity essentially changes the thermal performance only. The pyrolysis gas flow is hypothesized to contribute to the thermal response of the material as it convects energy through the porous medium. Nomenclature A= face area of a control volume, m 2 A i = pre-exponential factor of solid component i, s −1 E i ∕R = activation energy of solid component i over universal gas constant, K E g = overall gas energy per unit volume, J∕m 3 or kg∕m s 2 E s = overall solid energy per unit volume, J∕m 3 or kg∕m s 2 Fo = Forcheimer number H = gas enthalpy, J∕kg K = material sample permeability, m 2 L = arc length; distance to the origin of Cartesian coordinate system,, kg∕m 2 s p = static pressure, Pa p w = sample surface pressure (p w 0 is the stagnation value), Pa q w = sample surface heat flux (q w 0 is the stagnation value), W∕m 2 S D = source term accounts for the energy loss in porous media flow, kg∕m s 3 T = temperature, K T react = reaction initiate temperature, K t = time, s V = volume of a control volume, m 3 Γ i = volume fraction of virgin solid composite i Δ = discretized term ϵ = small perturbations in numerical Jacobians calculation θ = rotation angle around z-axis (counterclockwise) λ = solid material thermal conductivity, W∕mK ρ g = overall density of pyrolysis gases, kg∕m 3 ρ s = overall solid density, kg∕m 3 ρ s i = density of solid component i, kg∕m 3 ϕ = porosity of material ψ i = phenomenological parameter of solid component i in reaction forumula ω = reaction rate of gas/solid species, kg∕m 3 s D = (D x , D y , D z ), diffusive source terms in momentum equations, Pa∕m F cond = (F cond;x , F cond;y , F cond;z ), conductive heat flux, W∕m 2 n = face normal direction P = vector of primitive variables Q = vector of conservative variables RHS = right-hand side of the linear system to be solved S = vector of source terms in a control volume u = (u, v, w), velocity components of Cartesian coordinates, m∕s F = convective flux through the face of a control volume F d = diffusive flux through the face of a control volume Subscripts c = char state of the material g = overall pyrolysis gas IP = in-plane orientation i = solid component i max, min = maximum and minimum values of boundary conditions s = overall solid TTT = through-the-thickness v = virgin state of the material w = sample surface wall x, y, z = components of Cartesian coordinate system

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“…20 This code solves the charring ablator, general porous flow, and heat transfer problems in serial or parallel. In the present application, the tiles neither char nor ablate.…”

Section: Conduction Modelingmentioning

confidence: 99%

Assessment of CFD Hypersonic Turbulent Heating Rates for Space Shuttle Orbiter

Wood

Oliver

2011

42nd AIAA Thermophysics Conference

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Turbulent CFD codes are assessed for the prediction of convective heat transfer rates at turbulent, hypersonic conditions. Algebraic turbulence models are used within the DPLR and LAURA CFD codes. The benchmark heat transfer rates are derived from thermocouple measurements of the Space Shuttle orbiter Discovery windward tiles during the STS-119 and STS-128 entries. The thermocouples were located underneath the reaction-cured glass coating on the thermal protection tiles. Boundary layer transition flight experiments conducted during both of those entries promoted turbulent flow at unusually high Mach numbers, with the present analysis considering Mach 10-15. Similar prior comparisons of CFD predictions directly to the flight temperature measurements were unsatisfactory, showing diverging trends between prediction and measurement for Mach numbers greater than 11. In the prior work, surface temperatures and convective heat transfer rates had been assumed to be in radiative equilibrium. The present work employs a one-dimensional time-accurate conduction analysis to relate measured temperatures to surface heat transfer rates, removing heat soak lag from the flight data, in order to better assess the predictive accuracy of the numerical models. The turbulent CFD shows good agreement for turbulent fuselage flow up to Mach 13. But on the wing in the wake of the boundary layer trip, the inclusion of tile conduction effects does not explain the prior observed discrepancy in trends between simulation and experiment; the flight heat transfer measurements are roughly constant over Mach 11-15, versus an increasing trend with Mach number from the CFD. Nomenclature

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Development and Verification of the Charring Ablating Thermal Protection Implicit System Solver

Cited by 46 publications

References 20 publications

Mach 6 Wake Flow Simulations Using a Large-Eddy Simulation/Reynolds-Averaged Navier–Stokes Model

Mach 6 Wake Flow Simulations Using a Large-Eddy Simulation/Reynolds-Averaged Navier–Stokes Model

Numerical Investigation of Thermal Response Using Orthotropic Charring Ablative Material

Assessment of CFD Hypersonic Turbulent Heating Rates for Space Shuttle Orbiter

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