Jet-flap installation noise of pylon mounted jet engine on 3D wing

Abstract

The cost of experimental testing allows to focus only on a finite number of operations for installation noise. How can other operations be interpolated in between test conditions? How can test points with partially poor signal to noise ratio be repaired? How is it possible to extrapolate to and cross-compare with a known test point which is out of scope for the current test facility, but has been measured before in another wind tunnel? All of the above can be attempted with the knowledge of the problem-specific physics, which is among others represented in terms of velocity scaling laws. Hence, a major contribution presented in this paper is the analytical derivation of an analogy for the far-field noise of installed flight jets and a cross-check with experimental data from the DJINN AWB test. This analogy is a specific solution of Ffowcs-Williams-Hawking's and Curle's analogies for fixed objects which experience unsteady flow fluctuations on their surfaces. The analysis shows that velocity scaling exponents are qualitatively different depending on directivity, mainly between forward and rear arc. The experimentally acquired isolated flight jet noise data scales with I~(ΔU)⁶Uc² in the forward arc and with I~(ΔU)⁸ in the rear arc. Installed flight jets are dominated by loading noise I~(ΔU)⁶ in the forward arc, and are otherwise very similar to jet noise, i.e. in the rear arc they scale with I~(ΔU)⁸. The transition of velocity scaling coefficients between forward arc and rear arc are extracted by a study over 47 flyover microphones using various operations of either same shear layer difference velocity or same shear layer convection velocity. The exponents can also be used to improve the prediction of extrapolating to out-of-scope wind tunnel velocities.