Sound propagation through elevated, heated jets in cooler cross-flow: An experimental study.

Sound propagation through hot exhaust plumes with cooler cross-winds is present in many real world systems. One particular example is the sound propagation from exhaust stacks attached to open cycle gas turbine power stations. The research presented in this paper investigates the sound propagation from a reduced-scale exhaust stack, with a cross-flow from experiments conducted in a wind tunnel. Experimental measurements of the flow and temperature fields provide insight into the complex sound radiation characteristics. Results from the acoustic measurements show the change in the sound directivity arising from the inclusion of the hot exhaust plume, leading to non-axisymmetric sound directivity and a concentration of sound downwind of the exhaust stack outlet. In certain cross-flow conditions, the hot exhaust plume can increase the sound observed downwind by up to 11 dB when compared to the scenario of sound propagation from an exhaust stack in the absence of a heated jet or cross-flow. This paper describes the acoustic directivity at various radial distances from the exhaust stack, acoustic frequencies, jet temperatures, and cross-flow free-stream velocity. The results from this paper emphasise the importance of taking into consideration the hot exhaust plume with cooler cross-flow when estimating sound levels downwind of the stack.