Computation of Tone Noise from Supersonic Jet Impinging on Flat Plates

A supersonic jet impinging normally on a atplate has both practical importance and theo-retical interests. The physical phenomenon isnot fully understood yet. Research concen-trates either on the hydrodynamics (e.g. liftloss for STOVL) or on the aeroacoustic load-ing.In this paper, a nite volume scheme–thespace-time conservation element and solutionelement (CE/SE) method–is employed to nu-merically study the near-eld noise of an un-derexpanded supersonic jet from a converg-ing nozzle impinging normally on a at plate.The numerical approach is of the MILES type(monotonically integrated large eddy simula-tion). The computedresults comparefavorablywith the experimental ndings.1 IntroductionHigh speed impinging jets are important to aircraft in-dustry. For vertical landing and short take-off (STOVL)airborned vehicles propelled by jet engines, there are un-desirable and adverse effects from the impinging jets.These include up to 60% lift loss and the acoustic load-ing and noises generated by a feedback loop between thejet and the ground.Research on jet impinging normally on a at plate hasunfolded in a broad way. Some researchers concentrateon the hydrodynamics and investigate the lift loss, otherresearchers focus on the sound produced and the aeroa-coustic loading of the impinging jets. There are a vastnumber of papers published on these topics. For exam-ple, after carefulobservationsovertheexperimentaldata,Powell [1] pointed out that the small instability waves(vortices) around the jet shear layers and the consequentradial wall jet are responsible for the noise as they inter-act with the at plate and produce sound waves. Ho andNosseir [2] explained the feedback loop in the imping-ing jets; while Tam and Ahuja [3] put forward anothertheoretical model for the acoustic feedback loop. In themeantime, experimentalistsare conductingvarious phys-ical experiments in search for the feedback mechanismin different impinging jet situations. Alvi and Iyer [9]studied the impinging jet with lift plate, Krothapalli et al[8] investigate both the jets with convergent nozzle andconvergent-divergent(C-D) nozzles. Hendersonet al[4 -7] performed experimentsof sound producingimpingingjets on small and large plates.Numerical simulations of unsteady impinging jetshave also been carried out. Kim and Park [10] used thepopular TVD upwind scheme. Sakakibara and Iwamoto[11] also used TVD scheme to study oscillations in im-pinging jets and the generation of acoustic waves.In the present paper, a MILES (monotonically inte-grated large eddy simulation) type scheme is used to in-vestigate the problem of a jet impinging on a at plate.The MILES approach appears somewhat similar to LES,but there is no explicit ltering since the cell-averagingprocess is already equivalent to spatial ltering. Due tocertain built-in numerical dissipation in a MILES nitevolume scheme, the SGS (subgrid scale) model is notneeded. The recent space-time conservation element andsolution element method (CE/SE) [12-13] is a MILEStype nite volume method with generally less numeri-cal dissipation and is adopted for the computation. Asdemonstrated in previous papers, the CE/SE scheme iswell suited for aeroacoustics computation [15,16]. Be-cause of the CE/SE non-reecting boundary conditions(NRBC), which are based on the physics of plane wavepropagation [14], a smaller near eld computational do-main can be used in the present numericalsimulation andhelps to save both memory and CPU time.The governing equations and the 2-D axisymmetricunstructured Navier-Stokes (N-S) CE/SE scheme usedhere is briey reviewed in Section 2. Section 3 illustratesthe noise problems of an impinging jet on normal atplates, both large and small, with the initial and bound-