Numerical Prediction of Far-Field Combustion Noise from Aeronautical Engines

Abstract

A hybrid methodology combining a detailed Large Eddy Simulation of a combustion chamber sector, an analytical propagation model of the extracted acoustic and entropy waves at the combustor exit through the turbine stages, and a far-field acoustic propagation through a variable exhaust temperature field was shown to predict far-field combustion noise from helicopter and aircraft propulsion systems accurately for the first time. For the single-stream turboshaft engine, the validation was achieved from engine core to the turbine exit. Propagation to the far field was then performed through a modeled axisymmetric jet. Its temperature modified the acoustic propagation of combustion noise significantly and a simple analytical model based on the Snell–Descarte law was shown to predict the directivity for axisymmetric single jet exhaust accurately. Good agreement with measured far-field spectra for all turboshaft-engine regimes below 2 kHz stresses that combustion noise is most likely the dominant noise source at low frequencies in such engines. For the more complex dual-stream turbofan engine, two regime computations showed that direct noise is mostly generated by the unsteady flame dynamics and the indirect combustion noise by the temperature stratification induced by the dilution holes in the combustion chamber, as found previously in the turboshaft case. However, in the turboengine, direct noise was found dominant at the combustor exit for the low power case and equivalent contributions of both combustion noise sources for the high power case. The propagation to the far-field was achieved through the temperature field provided by a Reynolds-Averaged Navier–Stokes simulation. Good agreement with measured spectra was also found at low frequencies for the low power turboengine case. At high power, however, turboengine jet noise overcomes combustion noise at low frequencies.

Sound Pressure Level Analysis of a Liquid-Fueled Lean Premixed Swirl Burner with Various Quarls

“…Therefore, operational noise has to be minimized [16,17]. In the case of aviation engines, the contribution of combustion noise is notable at full thrust during takeoff [18,19]. Even though advanced airfoils with porous trailing edges can reduce airfoil noise [20], combustion is still a notable part of the acoustic emission [21].…”

Large eddy simulation on combustion noise in a non-premixed turbulent free flame: Effect of oxygen enhancement

“…They predicted the spectral distribution of sound pressure within the combustor with acceptable qualitative and quantitative agreement against measurements [23]. Another study predicted far-field combustion noise from helicopter and aircraft propulsion systems with LES of a combustion chamber sector, an analytical propagation model at the combustor exit, and a far-field acoustic propagation through a variable exhaust temperature [24]. The results of these researches reveal that the hybrid method is efficient in predicting combustion noise.…”

Numerical and Experimental Analysis of the Effect of Acoustic Loads on the Source Characterization for an Internal Combustion Engine Exhaust System

“…(12) shows that the 1D-AM can consider only the effect of a uniform flow field on sound propagation, whereas the large temperature and velocity gradient fields in the axial and lateral regions of the load pipe are ignored. Many studies have shown that a velocity discontinuity in a moving medium will change the transmission and reflection characteristics of acoustic waves [20] [21], and a temperature discontinuity has a major effect on the propagation directivity of the transmitted waves [22] [23]. Therefore, ignoring the temperature and velocity gradient fields in the load pipe will generate significant errors in the solution of the acoustic parameters of loads.…”