No abstract

Axial flow compressors have a limited operation range due to the difficulty controlling the secondary flow. Vortex generators are considered to control the secondary flow losses and consequently enhance the compressor’s performance. In the present work, a numerical simulation of three-dimensional unsteady compressible flow has been developed in order to gain insight into the nature of this flow. Based on the numerical simulation, the effects of vortex generators with variable geometrical parameters and their application inside the cascade are investigated. The predicted flow fields with and without the vortex generators are presented and discussed. For each configuration of vortex generator, the total pressure and loss coefficient are calculated. The predicted velocity and pressure distributions at different locations are compared with the predicted and measured values available in the literatures.

Boundary layer control plays a decisive role in controlling the performance of axial compressor. Vortex generators are well known as passive control devices of the boundary layer. In the current study, two nonconventional types of vortex generators are used and their effects are investigated. The used vortex generators are doublet, and wishbone. Three dimensional turbulent compressible flow equations through an axial compressor cascade are numerically simulated. Comparisons between cascade with and without vortex generators are performed to predict the effect of inserting vortex generator in the overall performance of the axial compressor. Results indicate that using vortex generators leads to eliminate or delay the separation on the blade suction surface, as well as the endwall. Furthermore, the effects of the vortex generators and their geometrical parameters on the aerodynamic performance of the cascade are documented. In conclusion, while the investigated vortex generators cause a slight increase in the total pressure loss, a significant reduction in the skin friction coefficient at the bottom endwall is found. This reduction is estimated to be about 46% using doublet and 32% using wishbone.

Secondary flows are noxious to axial compressor performance. To overcome and control those secondary flows, vortex generators are used as a passive control device. Controlling secondary flows will lead to a further improvements in the compressor performance. A new design of vortex generator is considered in this investigation in order to control secondary flows in axial compressor cascade at design and off-design conditions. Numerical simulations of a three-dimensional compressible turbulent flow have been performed to explore the effect of the vortex generators on the reduction of secondary flows. Six different incidence angles are used for the off-design operation investigations. Based on the simulation results, the pressure, velocity, and streamline are used to follow up the development of the secondary flows. Thence, total pressure loss coefficient, static pressure rise coefficient, difference in flow deflection angle, and diffusion factor are estimated. Results indicate that vortex generators have a significant effect on the development of secondary flows at off design operation as they cause a reduction in total pressure loss, they also affect the loading behavior of the cascade as they cause a slight change in the cascade deflection, and a slight decrease in the diffusion factor which causes unloading of the blade. Static pressure rise is significantly reduced at negative incidence angles while a slight reduction occurs at positive incidence angles. In a word, the new design of the vortex generator enhances the cascade aerodynamic performance and enlarges the operating range of the cascade towards the positive incidence region.