Sound directivity from a 250kW gas turbine exhaust system

Abstract

Experiments and numerical simulations have shown that sound radiated from vertically orientated hot exhaust stacks is strongly refracted away from the exhaust plume. In gentle cooler horizontal cross-flow, the plume bends downwards, which subsequently leads to increased refraction of the sound towards the horizontal plane downwind from the stack outlet. This paper builds upon previous research and reports on field trials of the sound directivity measured from a 250kW gas turbine (Turbine Technologies Minilab SR-30 Gas Turbine). The turbine was operated at two turbine shaft speeds, approximately 45,000RPM and 75,000RPM delivering exhaust jet flow speeds and temperatures of Mach Mj = 0.06-0.12 and Tj = 400°C-560°C, respectively, and with wind conditions ranging from calm to 8m/s. It was found that previous research could be reproduced in the field, with SPLs downwind of the exhaust stack 10-12 dB higher than spherical spreading predicts. The paper concludes with guidelines for acousticians to assist in far-field predictions of sound pressure levels arising from hot exhausts such as those found in gas turbine power plants.