Abstract
As an indirect noise source generated in the combustion chamber, entropy waves are widely prevalent in modern gas turbines and aero-engines. In the present work, the influence of entropy waves on the downstream flow field of a turbine guide vane is investigated. The work is mainly based on a well-known experimental configuration called LS89. Two different turbulence models are used in the simulations which are the standard k-ω model and the scale-adaptive simulation (SAS) model. In order to handle the potential transition issue, Menter’s ð-Reθ transition model is coupled with both models. The baseline cases are first simulated with the two different turbulence models without any incoming perturbation. Then one forced case with an entropy wave train set at the turbine inlet at a given frequency and amplitude is simulated. Results show that the downstream maximum Mach number is rising from 0.98 to 1.16, because the entropy waves increase the local temperature of the flow field; also, the torque of the vane varies as the entropy waves go through, the magnitude of the oscillation is 7% of the unforced case. For the wall (both suction and pressure side of the vane) heat transfer, the entropy waves make the maximum heat transfer coefficient nearly twice as the large at the leading edge, while the minimum heat transfer coefficient stays at a low level. As for the averaged normalized heat transfer coefficient, a maximum difference of 30% appears between the baseline case and the forced case. Besides, during the transmission process of entropy waves, the local pressure fluctuates with the wake vortex shedding. The oscillation magnitude of the pressure wave at the throat is found to be enhanced due to the inlet entropy wave by applying the dynamic mode decomposition (DMD) method. Moreover, the transmission coefficient of the entropy waves, and the reflection and transmission coefficients of acoustic waves are calculated.
Highlights
In the development of modern aeronautical gas turbines, combustion noise is getting more and more attention as it may lead to severe problems in both combustion chamber and turbine stages [1]
Since the amplitude of entropy wave is set as 100 K and the inlet temperature is around 400 K, as indicated in Figure 10b, when the temperature rises from 400 K to 500 K or decreases to 300 K, the air thermal conductivity increases or decreases by 20%, it could be considered as a factor that affects the heat transfer on the vane surface because the averaged heat transfer coefficient HSAS_ave in the forced case increased by 30% relative to the baseline case (MUR129_SAS, Brown pentagon line) on the pressure side
Another important reason for the variation of wall heat transfer is when the temperature rises from 400 K to 500 K or decreases to 300 K, the air thermal conductivity increases or decreases by 20%, it could be considered as a factor that affects the heat transfer on the vane surface because the averaged heat transfer coefficient HS′AS_ave in the forced case increased by 30% relative to the baseline case (MUR129_SAS, Brown pentagon line) on the pressure side
Summary
In the development of modern aeronautical gas turbines, combustion noise is getting more and more attention as it may lead to severe problems in both combustion chamber and turbine stages [1]. Wang [11] and Papadogiannis [12] evaluated the propagation mechanisms of the indirect combustion noise generated by entropy plane waves in the Oxford MT1 high pressure (HP) stage, and revealed the variation of the upstream and downstream entropy noise in the turbine guide vanes and blades. The present work investigated the variation of downstream acoustic characteristics of a turbine guide vane under the influence of the inlet entropy wave. Several baseline cases are shown comparing the two different turbulence models (the k-ω model [19] and the SAS model [20]) The distributions of both isentropic Mach number and heat transfer coefficients along the vane surface are investigated.
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