Rotating stall is a well-known aerodynamic instability in compressors that limits the operating envelope of aircraft gas turbine engines. An innovative method for delaying the most common form of rotating stall inception using an annular dielectric barrier discharge (DBD) plasma actuator had been proposed. A DBD plasma actuator is a simple solid-state device that converts electricity directly into flow acceleration through partial air ionization. However, the proposed concept had only been preliminarily evaluated with numerical simulations on an isolated axial rotor using a relatively basic CFD code. This paper provides both an experimental and a numerical assessment of this concept for an axial compressor stage as well as a centrifugal compressor stage, with both stages being part of a low-speed two-stage axial-centrifugal compressor test rig. The two configurations studied are the two-stage configuration with a 100 mN/m annular casing plasma actuator placed just upstream of the axial rotor leading edge (LE) and the single-stage centrifugal compressor with the same actuator placed upstream of the impeller LE. The tested configurations were simulated with a commercial RANS CFD code (ansys cfx) in which was implemented the latest engineering DBD plasma model and dynamic throttle boundary condition, using single-passage multiple blade row computational domains. The computational fluid dynamics (CFD) simulations indicate that in both types of compressors, the actuator delays the stall inception by pushing the incoming/tip clearance flow interface downstream into the blade passage. In each case, the predicted reduction in stalling mass flow matches the experimental value reasonably well.

Rotating stall is a well-known aerodynamic instability in compressors that limits the operating envelope of aircraft gas turbine engines. An innovative method for delaying the most common form of rotating stall inception using an annular DBD (Dielectric Barrier Discharge) plasma actuator had been proposed. A DBD plasma actuator is a simple solid-state device that converts electricity directly into flow acceleration through partial air ionization. However, the proposed concept had only been preliminarily evaluated with numerical simulations on an isolated axial rotor using a relatively basic CFD code. This paper provides both an experimental and a numerical assessment of this concept for an axial compressor stage as well as a centrifugal compressor stage, with both stages being part of a low-speed two-stage axial-centrifugal compressor test rig. The two configurations studied are the two-stage configuration with a 100 mN/m annular casing plasma actuator placed just upstream of the axial rotor leading edge, and the single-stage centrifugal compressor with the same actuator placed upstream of the impeller leading edge. The tested configurations were simulated with a commercial RANS CFD code (ANSYS CFX) in which was implemented the latest engineering DBD plasma model and dynamic throttle boundary condition, using single-passage multiple blade row computational domains. The CFD simulations indicate that in both types of compressors the actuator delays the stall inception by pushing the incoming/tip clearance flow interface downstream into the blade passage. In each case, the predicted reduction in stalling mass flow matches the experimental value reasonably well.

This paper describes a preliminary assessment of two flow control strategies for improving the adiabatic efficiency of centrifugal compressors for aero-engine applications. Given that the diffuser loss and pressure recovery play and important role in centrifugal stage efficiency, a centrifugal compressor with “fishtail” pipe diffusers is chosen for the study. This type of diffuser, which is among the most efficient diffusers, turns the flow directly from a high-swirl radial flow toward an axial flow, thus providing a smaller outer compressor diameter. As such, they are ideal for aero-propulsion applications. Past researches indicate that the diffuser performance is very much dependent on the impeller exit flow (diffuser inlet flow) uniformity. Two passive candidate flow control strategies that could improve impeller exit flow uniformity are proposed, namely slots casing treatment near the impeller radial bend and flow recirculation with injection in this area. They are aimed at attenuating the significant low-momentum region near the shroud that grows from the radial bend to the impeller exit. Iterations of the two proposed flow control strategies were evaluated through unsteady RANS CFD simulations on a low-speed centrifugal compressor stage with fishtail pipe diffusers. A comparison in terms of component and stage performance as well as an analysis of the flow field was carried out from the simulation results of the early iterations of the two flow control strategies. They show that both strategies have good potential for improving impeller exit flow uniformity and reducing losses in the fishtail pipe diffusers. However, the casing treatment strategy is more promising for improving stage efficiency due to lower penalty in impeller efficiency.

Steam generator tube wear due to foreign objects (FOs) is a significant industry problem. Removal of foreign objects comes with challenges related to accessibility and the environment inside the steam generator. It is therefore of interest to estimate the rate of wear due to foreign objects lodged within the SG; particularly in the tube-sheet region. To estimate wear, the fluid forces acting on the FO are a key input. Much remains unknown regarding the characteristics of fluid forces acting on small objects located within tube arrays. In the work reported here, an exploratory study of fluid forces acting on complex geometry objects was done. Force measurements were conducted in a wind-tunnel on a range of objects to investigate the effect of object geometry on the drag coefficient and the parameters which may be used to develop drag coefficient correlations. Turbulence forces acting on FOs in a tube array were found to be intimately related to turbulence forces acting on the tubes themselves. A direct relation between the corresponding force PSDs, via turbulence force correlations, is reported. This is a potentially useful result with regard to the nature of fluid forces acting on foreign objects in general.