Estimation of the maximum instantaneous distortion

Abstract

IN this synoptic, a new statistical method of estimating the maximum instantaneous inlet pressure distortion is described. By this method, the time average and root-meansquare (rms) values of the instantaneous pressure distortion index Ke, Krad, and KA2 can be obtained analytically from the measured inlet total steady-state pressure and rms values. The most probable maximum instantaneous distortion index that occurs in a given duration can also be obtained. Comparison between the estimated values and the experimental results shows that the described method can estimate accurately the maximum instantaneous distortion index with 3 s on an Intel 86/330 microcomputer. Contents In the evaluation of inlet and engine compatibility of a new aircraft, the maximum instantaneous pressure distortions of the intake are usually estimated in the earlier stages of the development to forecast whether they are greater than the allowable values of the engine. There are three well-known statistical estimating methods discussed in Ref. 1. In this paper, the time average and rms values of the instantaneous distortion index K6, Krad, and KA2 are obtained analytically from inlet total steady-state pressure and rms measurements beforehand. By assuming that the amplitude probability density distribution of the distortion index is Gaussian, the most probable probability with which the maximum instantaneous distortion value occurs in a given duration and the maximum instantaneous distortion itself are found. This method is of practical value if the distortion pattern that pertained to the maximum instantaneous distortion is not indispensable as in the preliminary design stage of the intake. The distortion index K can usually be expressed as