8th European Symposium on ATD for Space Vehicle, Lisbon, 2-6 March 2015

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2 FAST a Pre-Design Tool for the Atmospheric Re-entry of Space Vehicles and Debris F. Sourgen (*) Y. Prévereaud J-L. Vérant E. Laroche J-M. Moschetta (*) frederic.sourgen@onera.fr Onera Midi Pyrénées Center BP 7405 FR France

3 Outline Code Structure CAD Analysis and General ATD Environment Aerothermodynamics Modelling (Multi-physics modelling is not presented here) Space Vehicles and Debris - Capsules (AOTV ARD) - Vehicle (Pre-X) - Orbital debris re-entry experiment (Cubesat) 3

4 Code structure Forces & Momentum 3D distributions Faceted surface normals computation Aerodynamic coefficients Integrate Pressure and friction coefficients Continuum rarefied flow General aerodynamic environment computation Local pressure value Flight point data Reference Wall Temperature (stagnation point) Radiative equilibrium or ablation Local wall temperature Radiative equilibrium or ablation Reference heat flux (stagnation point) Local heat flux Continuum rarefied flow Curvature radius computation General aerodynamic environment computation Flight point data 4

5 Pre-processing (CAD analysis & general ATD environment) Shock wave Body F( x y z) = 0 F( x y z) = ax + by r r F( x y z) n F = F( x y z) r r C = / r = n 1 F + cz + dxy + exz + fyz + gx + hy + iz + l Momentum & energy Equilibrium Divergent unconstrained method (many methods available in FAST and in the literature) 5

6 Aerodynamic coefficients Continuum flow C p ( M ) = C cos V. n( M ) p stag C p stag = P stag P P dyn P dyn 1 = ρ V General 3D object : Modified Newton model - Shock curve : Love Billig Modified Billig (Prevereaud et al. Onera) - Mass flow balance - Isentropic expansion from stag. point D or 3D Axisymmetrical object Non local model 6

7 Aerodynamic coefficients Continuum flow Modified Newton Method SPHERE Pressure Free-Stream Conditions 3.3Pa Temperature 06.7K Velocity Gas γ 705m/s Air 1.4 Cp Theta (degrees) CFD Modifed Newton (FAST) Non local method SPHERE- CONE Pressure Temperature Velocity Gas γ Free-Stream Conditions 03.5Pa 559K 4401m/s Air 1.4 7

8 8 Wall Heat flux Continuum flow - Verant-Sagnier formulation to define a reference value : - Propagation to any facet : - Radiation from shock layer : * Martin et al. Tauber et al. * Ferrier et al. (Onera) allows higher velocity values and larger objects applications (asteroids) - Wall enthalpy (equilibrium assumption) = ref w t N stag conv stag rt h H R P q ( ) 8 0. ) ( ) ( ) ( ) ( = + = β β α stag z y x R R N g rad stag conv stag total P z y x P z y x R R q q z y x q N ) ( = w w T T w w w e e T T Cp θ θ θ

9 Aero Coefficients and Wall Heat flux Rarefied flow - Free molecular flow : Bird s formulation - Transitional flow : Bridging functions Pressure and skin friction coefficients (0.001 < K n < 100) a n n have been calibrated using DSMC data fm cont ( C C ) tr cont C p f = C p f + f ( K n ) p f p f [ ( a + a K )] n f ( K n ) = sin π 1 log10 n Wall heat flux Only a n n values have been modified Heat flux coefficient at stagnation point of a sphere (FAST vs simulation data from Glass et Moss) 9

10 Capsules : AOTV Modified Newton Method vs Wells et al. experiments Non local method Modified Newton Method 10

11 Capsules : ARD AoA 0deg Mach number 15 FAST LORE (from Walpot et al) Local pressure coefficient - Onera S4 WT experiments - Rebuilding using LORE (Walpot et al.) Error FAST vs LORE (%) 11

12 Capsules : ARD AoA 0deg Mach number 15 Local pressure coefficient symmetry plane 1

13 Capsules : ARD AoA 0deg Mach number 15 & 4 Convective heat flux symmetry plane Rn/R QLORE Q FAST (Lep) Q FAST (VS) M E Rn/R QLORE QFAST(lep) QFAST(VS) M Q[W/m²] Rn/R Q[W/m²] Rn/R s/d s/d

14 Space Vehicles : Pre-X (IXV-like vehicle) Mach [-] Altitude [km] Velocity [m/s] Density [kg/m 3 ].579 x x 10-5 Temperature [K] Pressure [Pa] Wall conditions rad. Equilibrium Fixed at ε = K Flight point data (PRE-X phase A1) α = 40 β = 0 flaps deflection = 15. Pre-X vehicle (A1) IXV vehicle 14

15 Space Vehicles : Pre-X (IXV-like vehicle) M17.75 Local pressure coefficient FAST CELHyO (NS Park 5 species) 15

16 Space Vehicles : Pre-X (IXV-like vehicle) M17.75 Wall heat flux 16

17 Orbital Debris re-entry experiment (QB50 project IOD ISAE-Onera) «EntrySat» Objectives -ATD Environment-cinematics measurements during orbital phase -Few measurements during re-entry Z = 70km V=669 m/s «smooth config.» FAST (W/cm²) Navier-Stokes CEDRE (W/cm²) 17

18 Summary Geometrical components of the object are not separately processed but they are investigated by a global method taking into account some geometrical effects low time-consuming compared to Navier-Stokes simulations and it can easily be coupled to a trajectory computation program. The modelling developed for FAST allows computing a complete trajectory since continuum free molecular and transitional flow have been addressed. Elliptic flow regions mainly encountered by capsules and thermal shields cannot be correctly described by a Newtonian approach but it has been shown that results could be significantly improved by using non-local methods. Boundary layer thickness play a significant role for local heat flux assessment at trailing edges : BL modelling is to be performed. A prime important point concerning application to orbital debris risk assessment is the development of corrected laws taking account of partial catalicity at wall. In the case of orbital debris specific features such as tumbling of the object (unsteady heat flux values) strong curvature radius variations (due to the object design tumbling wall ablation) require additional modelling for aerothermodynamics. 18