Some results in combustion generated noise

Spectral Separation of the Turbofan Engine Coherent Combustion Noise Component

“…Further developments in scaling laws were derived by Strahle (1972Strahle ( , 1975 17, 18 involving the first Eulerian time derivative of the chemical reaction rate integrated over the reacting volume. A review of current theories of scaling laws is given by Strahle (1975).…”

Combustion‐Generated Noise: An Environment‐Related Issue for Future Combustion Systems

“…As napshot of intensity signals recorded by ah igh-speed camera and the corresponding time-averaged distribution from chemiluminescence measurements are shown in Figure 10 for ;¼0:9, which qualitatively illustratet he shape and length of the considered flame,a sw ell as positions of the reaction zone.A sm entioned before,t he imagesp resent line-of-sight summed values, and therefore,t he exact 3D flame surface cannot be resolved by this technique.T hese integral data can, however, be used to assess the acoustic source or the fluctuations of total heat releaser ate _ Q t by means of Equation (8). In doing so, _ Q t is calculated by summing up the intensityd ata gathered on each pixel of the image for each sample time.F igure 11 shows the temporal evolutionof _ Q t evaluated from the chemiluminescence measurements,w hich is then applied to Equation (3) for prediction of the combustion noise in the following section.…”

“…[7,23,[34][35][36] Thus,L ighthillso riginal equation was recast to aw ave equation with solely the unsteady heat release as the dominant source [Eq. (1)]: [7,8,18] 1 c 2…”

“…[3,5,6] Thec urrent work is focused on predicting the direct combustion noise emitted from unconfined,p remixed flames.I nl ow-Mach number (Ma) combustion flows,t he fluctuation in heat release,c aused by the interaction of the chemical reactions and the turbulent flow, represents the main noise-generating source. [7,8] As ac onsequence,c ombustion noise correlates strongly with turbulent fluctuations and is broadband in the spectral domain. Locally,i ta ppearsa sa nu nsteady generation of volumei nt he reaction zone.T he rate of changei nv olumed epends on the Af irst-ordere stimation of the prediction of combustion-generated noise from turbulent premixed flames was explored.…”

“…[17] Although the acoustic equations used for the CAA modeling have different mathematicalf ormulations,t hey are all deduced from the basic balancee quations of the flow (mass,m omentum, and energy).M oreover, most of the CAA equations can be rearranged to includet he heat releasea st he dominant acoustic source. [4,11,18] An integral solution of Lighthillse quation was derived by Strahle [7,8] for modeling combustion noise,w ith the unsteady heat release used as the main acoustic source.T he method postulates that the entire turbulent flame may be considered as ac ollection of locally distributed monopole sources with fluctuating heat releaset hat interact with each other in ac oherentf lame volume. Theo verall noise contributionf rom these source elements on af ar-field location is given by the integration of the unsteadyh eat release over the whole flame volume.T his analytical solution is attractive and is followed by different authors because ac omputationally intensive solution of an acoustic equationo rs ystem of equations is not necessary.H owever, its direct applicationr equires that the heat release rate be resolved temporally and spatially, which is time consuming.…”