Dynamics of a shock wave train induced by downstream flow oscillations
Creators: name:  E. BEKAERT 
name:   A. GENOT 
name:   T. LE PICHON 
name:   T. SCHULLER 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: PROPULSION PHYSICS
AIR BREATHING
RAMJET
SCRAMJET

description: Dynamics of a shock wave train induced by downstream flow oscillations Erwin BEKAERT, Aurelien GENOT, Thomas LE PICHON DMPE, ONERA, Universite Paris Saclay, 91123 Palaiseau, France erwin.bekaert@onera.fr, aurelien.genot@onera.fr, thomas.le_pichon@onera.fr Thierry SCHULLER Institut de Mecanique des Fluides de Toulouse, Universite de Toulouse, CNRS, 31062 Toulouse, France thierry.schuller@imft.fr The ramjet is an air-breathing propulsion system well-adapted for supersonic speeds, between Mach 2 and Mach 5. As for other propulsion systems, its extreme operating conditions may facilitate the triggering of thermoacoustic instabilities which can lead to premature extinctions or chamber damages. Thermoacoustic instabilities have been experimentally identified in the ONERA experimental bench \"Research Ramjet\" (Statoreacteur de Recherche (SdR)). The SdR has been designed in order to examine the basic physical phenomena governing the flow dynamics and build up an experimental database as a mean to assess and validate numerical flow simulations. The SdR is a two-inlet side-dump combustor, which can be operated with gaseous or liquid fuels for operating conditions that are representative of flight conditions. This combustor was designed for direct-connected tests. Consequently, the air inlets shown on the setup in Fig. 1 have been simplified compared to a flight vehicle ; however, as in real diffusers, pseudo shocks develop downstream the sonic throats. Self-sustained combustion oscillations were found to be coupled to two acoustic longitudinal modes taking place inside the combustor and the air-inlet inlet cavities [1]. When acoustic oscillations propagate upstream inside the air inlet, they are reflected by the shock wave train downstream the sonic throat leading also to a cyclic displacement of this structure inside the flow. This in turn leads to a change of the volume and acoustic characteristic length over which the acoustic mode develops. These modifications intensely alter the flow dynamics and therefore, the combustion inside the chamber. In order to model the unsteady behavior of the combustor, it is necessary to characterize the motion and the response of the shock wave train inside the air inlet when it is submitted to flow oscillations. See Abstract file Figure 1: Schematic of the ONERA Research Ramjet and the studied zone encircled by dotted lines Large-eddy simulations with the ONERA flow solver CEDRE [2] are conducted to analyze the pseudo-shock response to acoustic perturbations and its motion when it is submitted to downstream pressure oscillations. The numerical setup only considers the air inlet pipe shown in Fig. 1. Pressure disturbances are simulated by imposing a sinusoidal signal at the numerical domain outlet. The amplitude and the frequency of the forcing are varied. Results for the dynamics of the shock wave train are compared to analytical models developed for normal shocks [3, 4]. References [1] A. Roux. Simulation aux grandes echelles dun statoreacteur. 2009. [2] A. Refloch, B. Courbet, A. Murrone, P. Villedieu, C. Laurent, P. Gilbank, J. Troyes, L. Tesse, G.Chaineray, J-B. Dargaud, E. Quemerais, and F. Vuillot. CEDRE software. Aerospace Lab., vol. 2, Paper number AL02-11, 2011. [3] F.E.C. Culick and T. Rogers. The response of normal shocks in diffusers. AIAA J., Vol. 21, No. 3, pages 13821390, 1983. [4] M. Sajben. Response of normal shocks in diffusers. AIAA J., Vol. 23, No. 3, pages 477478, 1985.