Delayed Detached Eddy Simulation of Supersonic Inlet Buzz

Transcription

1 Delayed Detached Eddy Simulation of Supersonic Inlet Buzz S. Trapier, S. Deck and P. Duveau Applied Aerodynamics Department

2 What is Supersonic inlet buzz? Supersonic air inlets supply the engine of an aircraft with air taken from the atmosphere. Inlet buzz : Undesirable phenomenon of selfsustained shock oscillations Shock expelled p i Engine Compression ramp(s) Diffuser Cowl lip M>1 Engine Shock swallowed p i Shocks M<1 2

3 CONTENTS I. Experimental study -Experimental setup / inlet model -Experimental results : pressure signals II. III. DDES simulation -Delayed Detached Eddy simulation -Grid and computational description -Results -Behavior of DDES functions Comparison experiment/simulation -Unsteady results : pressure signals, spectra, wavelet transforms IV. Conclusion 3

4 CONTENTS I. Experimental study -Experimental setup / inlet model -Experimental results : pressure signals II. III. DDES simulation -Delayed Detached Eddy simulation -Grid and computational description -Results -Behavior of DDES functions Comparison experiment/simulation -Unsteady results : pressure signals, spectra, wavelet transforms IV. Conclusion 4

5 Experimental study The experimental setup : Inlet model in the wind tunnel Cowl lip Sidewall Shlieren window Diffuser Cowl lip Shlieren window Compression ramps Boundary layer bleed Pressure sensors rakes Model equipped with 30 unsteady Kulite pressure sensors Tests conducted from Mach 1.8 to Mach 3 Compression ramps Boundary layer bleed Diffuser Adaptable configuration (Boundary layer bleed, perforated walls ) 5

6 Experimental study Pressure signals during a buzz cycle at Mach 1.8 K18 K14 PS33 Buzz cycle Static pressure (Pa) Frequency of oscillations : 18 Hz Time (s) Subcritical phase Subcritical phase (secondary oscillations) Supercritical phase External shock moving upstream Oblique shocks M>1 M<1 External shock oscillating M<1 Separated zone M>1 M<1 M>1 Sonic line M<1 M>1 Internal shock M<1 6

7 CONTENTS I. Experimental study -Experimental setup / inlet model -Experimental results : pressure signals II. III. DDES simulation -Delayed Detached Eddy simulation -Grid and computational description -Results -Behavior of DDES functions Comparison experiment/simulation -Unsteady results : pressure signals, spectra, wavelet transforms IV. Conclusion 7

8 DDES simulation DDES (Delayed Detached Eddy Simulation, Spalart et al., 2006) : GIS highy undesirable when Shock/TBL interaction are concerned DDES is a version of DES designed to ensure that attached boundary layers are treated in RANS, in order to avoid Modeled Stress Depletion. The length scale of «classical» DES : is replaced with : ~ ~ d DDES ddes 97 min( d, C Δ) = DES = d fd max(0, d CDES Δ) d : distance to the closest wall C DES : constant of the model Δ : mesh size : sensor equal to 0 in attached boundary layers f d 1 elsewhere in attached boundary layers, (like in RANS). elsewhere, ~ dddes (like in classical DES97). ~ d DDES = d = min( d, CDESΔ) 8

9 DDES simulation Grid and computational description: Diffuser Cowl lip Sonic throat The grid contains 20 millions points, 12 millions of which are located in the upstream zone (compression ramps and inlet section) FLU3M code developed by ONERA Timestep : s 5 sub-iterations 10 buzz cycles have been simulated (total physical time : 0.5 s) Compression ramps Total CPU cost : 1600 hours on 2 processors of NEC-SX8 (i.e. 800h/proc) 9

10 DDES simulation DDES simulation of buzz (M=1.8) Q criterion (white), isosurface M=1 (blue) and pseudo-schlieren visualization 10

11 DDES simulation DDES simulation of buzz (M=1.8) Q criterion (white), isosurface M=1 (blue) and pseudo-schlieren visualization 11

12 DDES simulation Behavior of the f d function : Attached flow u (m/s) Cowl lip Compression ramps fd (f d should be equal to 0 in attached boudary layers, 1 elsewhere) u (m/s) Red (f d =1) : DES zones Blue (f d =0) : RANS zones Separated flow fd Red (f d =1) : DES zones Blue (f d =0) : RANS zones f d behaves correctly both in attached and separated flows 12

13 CONTENTS I. Experimental study -Experimental setup / inlet model -Experimental results : pressure signals II. III. DDES simulation -Delayed Detached Eddy simulation -Grid and computational description -Results -Behavior of DDES functions Comparison experiment/simulation -Unsteady results : pressure signals, spectra, wavelet transforms IV. Conclusion 13

14 Simulation/experiment comparisons Comparison of unsteady results : Pressure (Pa) Pressure signals 2 1 x 10 5 Buzz cycle Secondary oscillations Time (sx10 4 ) expe URANS DDES PSD (Pa 2 /Hz) 10 8 DDES URANS Expe Spectra of pressure signals Buzz frequency (18 Hz) Frequency (Hz) The frequency of buzz, as well as higher frequencies, is correctly predicted by DDES. 14

15 Simulation/experiment comparisons Comparison of unsteady results : Wavelet transforms (distribution of the energy of a signal against time and frequency) DDES x x Experiment Pressure (Pa) 0 5 Pressure (Pa) Time (s) Frequency (Hz) Frequency (Hz) Buzz frequency (18 Hz) Time (s) Time (s) 15

16 Conclusion and perspectives Conclusion Buzz flow is well reproduced by the DDES Pressure levels and frequencies are correct The functions of DDES perform satisfactorily Perspectives The ability of numerical simulation to accurately predict the buzz limit is currently evaluated A methodology for this prediction is to be developed 16

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18 Simulation/experiment comparisons Comparison of phase-averaged results : (Buzz cycles are divided into 12 phases, and the data is averaged over each phase) Simulated pressure fields Location of experimental sensors Contours of M=1 p (Pa) Phase 3 (Secondary oscillations) Phase 6 (Supercritical) Phase 10 (Subcritical) Phase averaged pressure (Pa) Simulated and experimental pressure profiles on lower wall x 10 5 Phase 3 (Secondary osc.) DDES Phase 3 (Secondary osc.) Exp. Phase 6 (Supercritical) DDES Phase 6 (Supercritical) Exp. Phase 10 (Subcritical) DDES Phase 10 (Subcritical) Exp x (m) 18