Detached Eddy Simulation of Restricted Shock Separated flow in a Thrust Optimized Contoured nozzle

Detached Eddy Simulation of restricted shock separated (RSS) flow has been performed to understand the physics of complex cap-shock pattern, which is the key cause of separated flow transition in the rocket nozzles. High-order shock-capturing numerical schemes are necessary to understand this complex flow. Hence a fifth order monotonicity preserving weighted essentially non-oscillatory (MPWENO) scheme is used here for good numerical resolution

Reflection coefficients and screech-tone prediction in supersonic jets

International audienceWe study and model the resonance mechanism underlying the generation of A1 and A2 screech modes in an under-expanded supersonic jet. Following our previous work [1], where upstream-travelling guided jet modes were used to provide closure of the screech resonance loop, we here consider a more complete model in which both wavenumbers and frequencies of the upstream-and downstream-travelling waves are complex. The new model requires knowledge of the upstream and downstream reflection coefficients, which are treated as parameters and identified using the experimental data. The new screech model is shown to provide a more complete description of the measured data. I. Nomenclature c ∞ = Ambient speed of sound k = Dimensionless streamwise wavenumber ω = Non-dimensional frequency m = Order of the azimuthal Fourier mode n r = Radial order of the guided jet modes St = Nozzle diameter-based Strouhal number M a = Acoustic Mach number M j = Jet Mach number U j = Jet velocity T = Jet-to-ambient temperature ratio k K H = Kelvin-Helmholtz instability mode k p = Guided jet mode L 1 = Length of the first shock cell L s = Location of the s th shock cell Re = Nozzle diameter-based Reynolds number D = Nozzle diameter r = Radial distance from the nozzle axis SPSL = Sound Pressure Spectrum Level

Dynamics of round jet impingement

International audienceThe impingement of a round jet issued from a convergent nozzle is known to produce intense tonal noise. These tones are generated by a feedback process involving a Kelvin-Helmholtz instability wave and an upstream propagating wave. The frequency structure of these tones is experimentally explored by varying the jet Mach number from 0.7 to 1.5 and we observe evidence that neutral-upstream modes of the jet are active in the feedback process. Tone frequency predictions obtained using the intrinsic jet modes are compared to the standard model involving free-stream acoustic waves: the neutral waves model provides a convincing agreement with the experimental data

Mean Flow and Linear Stability Analysis of Twin Supersonic Jets

The mean flow and stability properties of perfectly-expanded supersonic twin-jet configurations are investigated by means of RANS calculations, spectral proper orthogonal decomposition (SPOD) based on experimental measurements and plane-marching parabolized stability equations (PM-PSE). A tailored twin-jet mean flow model is considered to assess its accuracy with respect to three-dimensional RANS twin-jet calculations. Mean-flow comparisons for different jet spacings suggest that the tailored model can provide a successful prediction of the actual twin-jet mean flow characteristics in the region close to the nozzle exit plane. However, further downstream, the tailored flow field presents strong deviations from the actual twin-jet mean flow, which increase in magnitude as the jet spacing is reduced. SPOD analyses applied to high-speed Schlieren visualizations provide the dominant coherent structures for the cases under study. Tonal peaks associated with Kelvin-Helmholtz instabilities showing flapping and toroidal fluctuations of the jet structure are found to concentrate a large portion of the spectral energy for all jet spacings. Complementary PM-PSE calculations based on the actual twin-jet RANS solutions show a very good qualitative agreement with SPOD modes in terms of the amplitude functions, enabling the identification of individual modes of oscillation of the twin-jet system

Joint European Effort Towards Advanced Rocket Thrust Chamber Technology

The achievements of the FSCD group during the last three years are described. For the case of nozzle flows in quiet ambience, new observations of the plume behaviour for truncated ideal nozzles are reported