Feasibility of using Single Mode Rings for Characterization of Turbine Tone Noise

Investigation on Turbine Tone Broadening in Static Engines

“…). Some of these findings are also observed by Matthews on their parametric studies for the JTD8 engine 7 Tone energy measured from cold flow rigs are converted into hot conditions 15,16 and the ground reflection and atmospheric absorption are applied so that the differences with the measured far field tone are expected to be the haystacking attenuation delta. If this phenomena can be modeled with one unique parameter, H, the delta obtained from different turbine tones, different rigs measured in different facilities and long and short cowl engines would correlate when plotted against H. Figure 9 shows these deltas for the three turbines powering engines labeled as A, B, C. The nomenclature for the turbine tones is XLPTY, where X is the temporal harmonic number and Y stands for the stage with the corresponding number of rotors.…”

“…The capability of cold flow rigs for measuring tone noise representative of the engine has been demonstrated beyond that obtained for the ANTLE engine using 'in-duct' measurements 16 , extending the comparison to the farfield and for three Rolls-Royce engines representative of a range of design styles and aircraft applications. Limitations already seen in the ANTLE assessment related to larger discrepancies for the tones coming from the forward part of the LPT have been also seen here.…”

“…Rig and engine comparisons previously done for the ANTLE 16 shows that rig measurements for the forward stages tones might not be representative, consequently, only rear stage tones are considered in the results shown on Figure 9. Engine A is a large civil engine with a short cowl, powered by a five stage LP turbine, for which the LPT rig was measured in the TST Facility in Derby.…”

“…Besides, there is no acoustic treatment downstream of the measurement plane so that measurements can be affected by reflections and facility noise. The acquisition of noise using a SMR can also be used for estimating the tone acoustic power although with an increased uncertainty 16 . This, together with the absence of the acoustic treatment, means that the reliability of these measurements is likely to be less than those acquired in the TSTF, something that has to be accounted in the analysis in the following sections.…”

“…As mentioned before, the present work will investigate if rig measurements are representative of the engine, and also if an existing semi-empirical model for haystacking is reasonably capable of modeling the phenomena. The first is something demonstrated 'in-duct' for the ANTLE Engine 15,16 , and now is investigated for three Rolls-Royce production engines representative of various design styles and thrust applications, and in the farfield for a static engine test. Since the haystacking can be highly dependent on the cold shear layer structure, and that significantly changes from static to flight conditions, some of the results and conclusions obtained here may differ when doing the analysis inflight, and that is something not addressed in the present work.…”