Experimental determination of noise source mechanisms in gas turbine combustors

Experiments were conducted to determine the cause(s) of gas turbine combustor noise and to quantify the portion of noise radiated from a combustor which is linearly, causally related to combustor events. Using multiple coherence analysis on results obtained with a combustor terminated by a choked nozzle-diffuser combination it was found that a) a two source model is adequate with the two sources being direct combustion noise and entropy noise, b) entropy noise is only important at low frequencies, but is highly coherent with combustion noise, c) with a choked nozzle termination the noise is higher frequency than previously demonstrated and d) some other, uncertain, source contaminated the results.