Low frequency noise generated by industrial gas turbines

The silencing of the exhaust from industrial gas turbines is an important element of current designs as it can affect efficiency, space, noise and gas emissions. However, exhausts are very costly and the lower the frequency, the higher is the cost involved in trying to attenuate the noise due to the amount of material and space necessary to implement the exhaust system. In this work, the sources of noise from an exhaust system of a particular gas turbine are investigated. Improvements in understanding the unsteady behaviour of the flow in the exhaust system could potentially lead to an increase in efficiency, a reduction in noise emissions, a decrease in the cost of exhaust mufflers and improved location for the plants. This work presents the experimental approach used to identify the major sources of noise and how these results were then used to create a model that could represent the sources identified. As the frequency components generated by the flow are low, this work concentrates on understanding the mechanisms that generate the low frequency noise. Results show that the major source of noise is the jet leaving the engine exhaust and that the main acoustic source is of dipole nature.