A numerical investigation of sound generation in supersonic jet screech

Abstract

Public reporting burden for this collection of information is estimated to average 1 hour per response, including gathering and maintaining the data needed, and completing and reviewing the collection of information. Send collection of information, including suggestions for reducing this burden, to Washington Headquarters Services Davis Highway, Suite 1 204, Arlington, VA 22202-4302, and fcV-tW 0Vf*si?of Management and Budget, Paper« AGENCY USE ONLY (Leave blank)2. REPORT DATE 11/29/00 REPORV-AFRL-SR-BL-TR-00-öürtl i. mm UM I i:a lUVbHbU 04/01/98-'09/30/00 TITLE AND SUBTITLE(U) A Numerical Investigation of Sound Generation in Supersonic JET Screech AUTHOR(S)Ted A. Manning and Sanjiva K. Lele FUNDING NUMBERSF49620-98-1-0355 The noise : i supersonic jet flows is due in part to the interaction between jet instability waves and the jet shock-cell structure. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)DEPARTMENTThe emitted shock-cell noise re-excites certain instability wave modes at the nozzle lip and causes resonant feedback to occur. This feedback resonance, known as supersonic jet screech, causes the jet to flap violently at discrete frequencies and generate very strong, narrow-banded tones. Jet screech is a source of acoustic fatigue in the tail and nozzle structures of supersonic aircraft. It is therefore important that methods for predicting the screech amplitude be developed.In the present research we investigate the screech sound generation process, particularly for high amplitude instability waves. We isolate the interaction of an unsteady shear layer with a single oblique shock. To obtain an overall understanding of the phenomenon with fewest simplifications, we study this problem through the numerical solution of the Navier-Stokes equations. We then consider idealizations to obtain a similar but wider range of results with specially linearbed Euler equations. These results motivate the use of geometric acoustics to describe the screech generation process. The Navier-Stokes and Euler simulations have revealed important details about the interaction process, how the acoustic field results, and why the screech is so loud. AbstractThe noise of supersonic jet flows is due in part to the interaction between jet instability waves and the jet shock-cell structure. If no counter-measures are taken, the emitted shock-cell noise will re-txcite certain instability wave modes at the nozzle lip and cause resonant feedback to occur. This feedback resonance, known as supersonic jet screech, causes the jet to flap violently at discrete frequencies and generate very strong, narrow-banded tones. Jet screech has been shown to be a source of acoustic fatigue in the tail and nozzle structures of supersonic aircraft. It is therefore important that methods for predicting the screech amplitude be developed. While comprehensive screech models will require taking all elements of the feedback loop into consideration, a basic understanding of each element in isolation will also be necessary. Screech sound generation is one such ...

Shock-Refracted Acoustic Wave Model for Screech Amplitude in Supersonic Jets

“…Numerical simulations by Manning and Lele [26] for a single shear layer-compression wave interaction suggest that the radiated acoustic pressure amplitude approaches a saturation level at increased distances from the origin of the shear layer (Fig. 7c).…”

“…Whereas screech frequency is controlled by the feedback acoustic waves, the screech intensity is governed primarily by the characteristics of the downstream propagating flow disturbances and their interaction with the shock-cell structures. Several detailed measurements [10,12,15,[19][20][21][22][23] and numerical viscous simulations [10,[24][25][26][27][28][29] have been reported and served to throw light on the subject. The experimental description of A-D mode switch (A1 , A2 , B, C, D) according to the jet operating parameters represents a notable step [12].…”

A second golden age of aeroacoustics?

“…Another important trend is the use of simulations to discover important unsteady flow phenomena associated with strong sound emissions. Leakage of shock waves trapped in the supersonic core flow of pressure-mismatched jets [71][72][73][74] enabled by strong vortices and the recent discovery that crackle, which is a particularly annoying noise, originates as a shocklet embedded within energetic eddy motions [75,76] are just two examples.…”

Time-dependent prediction of the unsteady pressure near-field from an under-expanded jet

“…This detail is provided independently by numerical simulations by Manning and Lele, 11 where numerical simulations of a vortex sheet past an oblique shock, modelled as a finite-thickness compression wave, is presented. In Manning and Lele, 11 the vortex sheet is artificially perturbed by a spatial pattern of downstream convecting vortices.…”