Numerical simulation and modelling of the effect of film cooling on entropy noise in a stator blade row

The entropy wave is therefore accelerated at a higher rate, leading to additional entropy noise.<br><br>3D simulations demonstrate that a cooling mass flow increase of only 3.4% with respect to the freestream amplifies the entropy noise generation by over 12%. Since the cooling flow is contained near the blade surface, the planar entropy wave experiences limited extra attenuation due to increased shear dispersion. This is found to scale with the additional mass flow rate of the coolant. <br><br>An analytical model has been extended to account for a film cooling flow by relaxing mass conservation across the blade row and by assuming perfect mixing.

Hence, entropy is not conserved across the row. The trend of entropy wave attenuation with increasing cooling flow is well predicted by the extended model, with a slight overestimation of ~4% compared to the high fidelity CFD simulations. The trend of rising entropy noise with an increasing cooling flow is also captured for the transmitted entropy noise transfer function.

However, the prediction of the reflected entropy noise is over estimated by 6.5%, and diverges with increasing mass flow ratio. Analysing the impact of the temperature ratio between the coolant and the freestream, it has been shown that a decrease in the ratio leads to a monotonic increase in entropy wave attenuation.