The aim of this work is an investigation into propagation effects on the low pressure turbine noise signature in a static engine environment, with special focus on tone broadening due to the transmission through the hot and cold shear layers. This is done empirically by the comparison of measurements in the farfield of a static noise test with the same turbine standard measured in a full scale cold flow noise rig. The work is done for three turbines, representative of different design styles and thrust range. Comparisons are intended to investigate, firstly, if rig measurements are representative of engine noise in the farfield. Secondly, if an existing tone broadening semi-empirical model is reasonably able to capture the physical effects, looking for the major issues to serve as basis for further research. For one of the engines, this technique based on rigs is compared with a different engine source diagnostic method. This consists of estimating the low pressure turbine contribution by comparing measurements with an acoustically treated and untreated hot duct.
NomenclatureLPT = Low Pressure Turbine ACARE = Advisory Council for Aeronautics Research in Europe TURNEX = Turbomachinery Noise Radiation Through the Engine Exhaust ANTLE = Affordable Near Term Low Emissions CNA = Common Nozzle Assembly TSTF = Twin Shaft Test Facility NMM = Noise Measurement Module ILA = Institut für Luftfahrtantriebe SMR = Single Mode Ring ρ = Flow density c = Flow speed of sound V = Flow velocity µ = Flow viscosity f = Frequency L = Distance between Hot and Cold Nozzles exit H = Haystacking parameter W = Acoustic Power PWL = Acoustic Power in dB scale Re = Reynolds Number M = Mach Number ∆ = Delta in dB due to Haystacking b = Characteristic frequency bandwidth 2 Sub/Superscripts () amb = Ambient conditions () cold = Bypass flow conditions () hot = Core flow conditions () Tone = Tone noise () BB = Broadband noise () BBO = Overall Broadband noise energy () BBN = Narrowband broadband noise () BBP = Peak broadband noise () Unhay = Noise before passing through the shear layer () Hay = Noise after passing through the shear layer () Loss = Loss of energy in the haystacking () Eng/Off = Engine noise in absence of acoustic treatment in the hot duct () Eng/On = Engine noise in presence of acoustic treatment in the hot duct () LPT/Off = Turbine noise in absence of acoustic treatment in the hot duct () LPT/On = Turbine noise in presence of acoustic treatment in the hot duct () No-LPT = Non-Turbine noise sources coming from the engine