Aeroacoustics Of Flow Over Rectangular Cavities

Unsteady Reynolds Averaged Navier Stokes (URANS) computations were performed to simulate flow past a rectangular cavity with free stream Mach number of 0.3. Deep cavity geometry was used with L/D ratio of 0.21. Frequency spectrum of the time accurate pressure data obtained using both URANS and LES simulations for closed cavity case. The dominant frequency of the resonance in the cavity was obtained as 16 kHz for the closed cavity case both with URANS and LES simulations. By injection of %1 of the main stream mass flow from the bottom of the cavity for the same free stream Mach number, dominant frequency reduced to the 8 kHz. The unsteady flow structures and effect of injection on the cavity flow instability mechanism were analyzed in detail in terms of flow physics. It was shown that injection effects vortex-acoustic feedback loop, by lifting up the vortices near the trailing edge of the cavity. Moreover, with the effect of injection, pressure fluctuations increased from 280 Pa to the 650 Pa

Experimental Study Of Unsteady Wake Effect On A Film-Cooled Pitchwise-Curved Surface

Unsteady wake interactions with the near wall flow field occur when a surface is exposed to fluid flow past upstream rotating bodies. In the case of gas turbines, understanding such interactions are essential to better design cooling schemes on endwalls. In view of this, an experimental study has been conducted to determine the heat transfer coefficient and film cooling effectiveness on a pitchwise-curved surface which is subjected to unsteady passing wakes generated using a wake rod in a wall-normal orientation. The mainstream Mach number was maintained approximately constant at 0.03. A single row of cylindrical film holes with pitch to diameter ratio of 3 and inclined at 35° to the test surface are used for discrete film injection. The coolant to mainstream mass flux ratio (M) is varied between 0.25 and 1. A spoke-wheel type wake generator is used to produce unsteady wakes at two wake Strouhal numbers (S = 0.15, 0.3). Measurements are made for (i) steady mainstream flow (S = 0) which serves as a baseline case, (ii) mainstream flow with unsteady wakes, (iii) steady mainstream flow with film injection (iv) both (ii) and (iii) combined. The unsteady passing wakes mitigated jet lift-off at high coolant to mainstream momentum flux ratios. The maximum increase in film effectiveness was measured to be ≅16.35% at the jet centerline for M = 0.75, S = 0.3 at x/D = 2. At high coolant to mainstream mass flux ratios, a combination of increasing film jet turbulence and strong interaction with the mainstream, deteriorates film cooling effectiveness but increases the heat transfer coefficient. Heat transfer augmentation increased by ≅7.6% for the highest wake passing frequency (S = 0.3) without film injection. A combination of unsteady passing wakes and film injection resulted in a maximum pitch-averaged and centerline heat transfer augmentation of ≅28% and 31.7% respectively