The effects of jet flow-rate modulation were investigated in the case of a 35 deg inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records, and large eddy simulations (LES). An unforced jet study was conducted over a wide range of blowing ratios to provide a baseline for comparison to the pulsed results. The two distinct and well known steady jet regimes (attached jet with high film cooling performance for BR < 0.4 and detached jet with poor film cooling performance for BR > 1.0) were related to the dynamics of characteristic vortical structures, significant in the transition from one regime to the other. Similarity of the inclined jet results with a past vertical jet study are also put in perspective when comparing wall adiabatic effectiveness results. 3D proper orthogonal decomposition (3D-POD) was performed on LES results of an unforced case at BR = 0.15 to provide an analysis of dominant modes in the velocity and temperature fields. Error calculations on the reconstructed fields provided an estimation of the number of modes necessary to obtain satisfactory reconstruction while revealing some of the shortcomings associated with POD.

The effects of jet flow-rate modulation were investigated in the case of a 35 deg inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records, and large eddy simulations (LES). In forced experiments, average blowing ratios of 0.3 and 0.4 were investigated with a duty cycle of 50% and pulsing frequencies of St = 0.016 and 0.159. Time-resolved flow rate measurements during the experiments provided precise knowledge of the instantaneous jet blowing ratio and adequate inlet boundary conditions for large eddy simulations. The dynamics of the vortical structures generated during the transient parts of the forcing cycle as well as their impact on film cooling performance were investigated with respect of the forcing parameters. At the considered blowing ratios, a starting ring vortex was consistently generated at the transition from low to high blowing ratio. Ingestion of cross-flow fluid at the transition from high to low blowing ratio was also observed and had a negative impact on film cooling performance. All studied cases exhibited an overall decrease in coverage regardless of pulsing parameters over their corresponding steady jet cases at fixed mass flow rate. Comparisons between pulsed and steady jets at constant pressure supply (same high blowing ratio) did exhibit some film-cooling improvement with pulsing. 3D Proper orthogonal decomposition was performed on LES results at distinct forcing frequencies to provide an analysis of dominant modes in the velocity and temperature fields. Significantly different results were obtained depending on the forcing frequency.

The effects of jet flow-rate modulation were investigated in the case of a 35° inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records and large eddy simulations (LES). An unforced jet study was conducted over a wide range of blowing ratios to provide a baseline for comparison to the pulsed results. The two distinct and well known steady jet regimes (attached jet with high film cooling performance for BR<0.4 and detached jet with poor film cooling performance for BR>1.0) were related to the dynamics of characteristic vortical structures, significant in the transition from one regime to the other. Similarity of the inclined jet results with a past vertical jet study are also put in perspective when comparing wall adiabatic effectiveness results. 3D Proper Orthogonal Decomposition (3D-POD) was performed on LES results of an unforced case at BR = 0.15 to provide an analysis of dominant modes in the velocity and temperature fields. Error calculations on the reconstructed fields provided an estimation of the number of modes necessary to obtain satisfactory reconstruction while revealing some of the shortcomings associated with POD.

The effects of jet flow-rate modulation were investigated in the case of a 35° inclined jet in cross-flow over a flat plate using Mie scattering visualizations, time-resolved flow rate records and large eddy simulations (LES). In forced experiments, average blowing ratios of 0.3 and 0.4 were investigated with a duty cycle of 50% and pulsing frequencies of St = 0.016 and 0.159. Time-resolved flow rate measurements during the experiments provided precise knowledge of the instantaneous jet blowing ratio and adequate inlet boundary conditions for large eddy simulations. The dynamics of the vortical structures generated during the transient parts of the forcing cycle as well as their impact on film cooling performance were investigated with respect of the forcing parameters. At the considered blowing ratios, a starting ring vortex was consistently generated at the transition from low to high blowing ratio. Ingestion of cross-flow fluid at the transition from high to low blowing ratio was also observed and had a negative impact on film cooling performance. All studied cases exhibited an overall decrease in coverage regardless of pulsing parameters over their corresponding steady jet cases at fixed mass flow rate. Comparisons between pulsed and steady jets at constant pressure supply (same high blowing ratio) did exhibit some film-cooling improvement with pulsing. 3D Proper orthogonal decomposition was performed on LES results at distinct forcing frequencies to provide an analysis of dominant modes in the velocity and temperature fields. Significantly different results were obtained depending on the forcing frequency.

This paper presents a Computational Fluid Dynamics (CFD) study performed to assess the prediction of the minimum stable volume flow for a high Mach number, high head, and high volume flow compressor stage. CFD was run on a “pie slice” or sector stage model in steady-state condition and on a full 360° stage model under both steady and unsteady state conditions. The predictions of the minimum stable flow were compared to experimental data. Results showed the CFD performed on the “pie slice” stage model over-predicted the minimum stable flow by 9% compared to the test results, while the transient CFD predicted the minimum stable flow within 5.8%. Flow field comparisons of the impeller between unsteady and steady state CFD revealed that the steady state CFD accurately predicted the flow phenomena until the onset of surge. However, the unsteady flow features could not propagate through the diffuser because of the limitations of the impeller-diffuser interface modeling in the steady state analysis.