Advanced turboprop noise prediction based on recent theoretical results

Abstract

This paper is about the development of a high speed propeller noise prediction code at Langley Research Center. The code utilizes two recent acoustic formulations in the time domain for subsonic and supersonic sources. The selection of appropriate formulation is automatic in the code. The structure and capabilities of the code are discussed. Grid size study for accuracy and speed of execution on a computer is also presented. The code is tested against an earlier Langley code. Considerable increase in accuracy and speed of execution are observed. Some examples of noise prediction of a high speed propeller for which acoustic test data are available are given. A brisk derivation of formulations used is given in Appendix 1.

Acoustic Radiation From Rotating Blades—the Kirchhoff Method in Aeroacoustics

“…The full solution of the FW}H and the K equations for sources on a panel moving at any speed have been given but, in particular at supersonic speed. It is believed that this result is suitable for development of an e$cient computer code so long as we limit the use to supersonic panels [31]. For the thickness and loading terms of the FW}H equation, the resulting analytic expression after taking all the derivatives explicitly, is a very complicated result known as the formulation 3 of Farassat [30,31].…”

“…It is believed that this result is suitable for development of an e$cient computer code so long as we limit the use to supersonic panels [31]. For the thickness and loading terms of the FW}H equation, the resulting analytic expression after taking all the derivatives explicitly, is a very complicated result known as the formulation 3 of Farassat [30,31]. Formulation 3 has been coded in the high-speed propeller noise prediction code ASSPIN [33] by Dunn.…”

“…In general, the formulations are very complicated and their derivation requires many algebraic manipulations [30,31]. In noise prediction codes, the data surface is divided into panels and the contribution of each panel to the noise is evaluated separately and summed.…”

Technical note: Preliminary work for modeling the propellers of an aircraft as a noise source in an acoustic boundary element analysis

“…Previous work on helicopter or aircraft propeller noise prediction has concentrated on computing the free field noise from a single propeller based on the Ffowcs Williams and Hawkings [6][7][8][9] integral equation which provides a solution to the noise radiated from a body in arbitrary motion. Work has been done 10,11 in evaluating this integral equation based on information about the geometry of the blade and its loading.…”

On Physical Aeroacoustics with Some Implications for Low-Noise Aircraft Design and Airport Operations

“…The first theory of aerodynamic noise applies equally [18][19][20][21][22][23] well to the to thickness (monopole), loading (dipole) and turbulence (quadrupole) noise of aircraft propellers [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] (Section 2.1.1), helicopter rotors [41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] (Section 2.1.2) and turbomachinery [56][57][58][59][60][61] requiring that the aerodynamic problem be solved first to specify the sources. The blade-vortex interaction noise (BVI) involves sound radiation by noise sources convected in a non-uniform flow, that does not match so well the assumptions of the first theory of aerodynamic sound of an unbounded medium at rest or in uniform motion with static or moving sources.…”