Stereo particle image velocimetry measurements focus on the flow structure and turbulence within the tip leakage vortex (TLV) of an axial waterjet pump rotor. Unobstructed optical access to the sample area is achieved by matching the optical refractive index of the transparent pump with that of the fluid. Data obtained in closely spaced planes enable us to reconstruct the 3D TLV structure, including all components of the mean vorticity and strain-rate tensor along with the Reynolds stresses and associated turbulence production rates. The flow in the tip region is highly three-dimensional, and the characteristics of the TLV and leakage flow vary significantly along the blade tip chordwise direction. The TLV starts to roll up along the suction side tip corner of the blade, and it propagates within the passage toward the pressure side of the neighboring blade. A shear layer with increasing length connects the TLV to the blade tip and initially feeds vorticity into it. During initial rollup, the TLV involves entrainment of a few vortex filaments with predominantly circumferential vorticity from the blade tip. Being shed from the blade, these filaments also have high circumferential velocity and appear as swirling jets. The circumferential velocity in the TLV core is also substantially higher than that in the surrounding passage flow, but the velocity peak does not coincide with the point of maximum vorticity. When entrainment of filaments stops in the aft part of the passage, newly forming filaments wrap around the core in helical trajectories. In ensemble-averaged data, these filaments generate a vortical region that surrounds the TLV with vorticity that is perpendicular to that in the vortex core. Turbulence within the TLV is highly anisotropic and spatially non-uniform. Trends can be traced to high turbulent kinetic energy and turbulent shear stresses, e.g., in the shear layer containing the vortex filaments and the contraction region situated along the line where the leakage backflow meets the throughflow, causing separation of the boundary layer at the pump casing. Upon exposure to adverse pressure gradients in the aft part of the passage, at 0.65–0.7 chord fraction in the present conditions, the TLV bursts into a broad turbulent array of widely distributed vortex filaments.

Three-dimensional flow structures and associated turbulence in the tip region of a waterjet pump rotor blade

Flow separation control using unsteady pulsed suction through endwall bleeding holes in a highly loaded compressor cascade

Experimental investigation of a counter-rotating compressor with boundary layer suction

Blade-end treatment to improve the performance of axial compressors: An overview

A non-standard aerodynamic design idea has been proposed for the supersonic or the transonic axial flow compressors. The aim of this non-standard design idea is to further increase the stage load efficiently with boundary layer suction used only in the stator, which can reduce the design difficulty of the air bleed system in the rotating part and improve the reliability of the stage. Compared with the conventional supersonic shock-in-type rotor, the rotor designed by this method can further increase the turning of the flow to enhance the stage work. Compared with the traditional supersonic impulse rotor, it can lower the rotor exit absolute Mach number to relieve the design difficulty of the downstream stator. But by increasing the turning of the flow in the rotor, the stator entrance Mach number will be increased inevitably, so boundary layer suction is used to solve its internal flow problems. Based on the numerical simulation, a verification stage has been designed to demonstrate the feasibility of thi...

Aerodynamic design of a highly loaded supersonic aspirated axial flow compressor stage

This paper presents results of numerical investigations carried out to explore the benefit of endwall boundary layer removal from critical regions of highly-loaded axial compressor blade rows. At the loading level of modern aero-engine compressors the performance is primarily determined by three-dimensional flow phenomena occuring in the endwall regions. 3DNS simulations were conducted on both a rotor and a stator test case in order to evaluate basic effects and the practical value of bleeding air from specific locations at the casing endwall. The results of the numerical survey demonstrated substantial benefits of relatively small bleed rates to the local flow field and to the performance of the two blade rows. On the rotor, boundary layer fluid was removed from the main flow path through an axisymmetric slot in the casing over the rotor tip. This proved to give some control over the tip leakage vortex flow and the associated loss generation. On the stator, boundary layer fluid was taken from the flow path through a single bleed hole within the passage. Two alternative off-take configurations were evaluated, revealing a large impact of the bleed hole shape and location on the cross-passage flow and the suction side corner separation. On both blade rows investigated, rotor and stator, boundary layer removal resulted in a reduction of local reverse flow, blockage and losses in the respective near-casing region. This paper gives insight into changes occuring in the 3D passage flow field near the casing and summarises the effects on the radial matching and pitchwise-averaged performance parameters, namely loss and deviation of the rotor and stator when suction is active. Primary focus is put on the aerodynamics in the blade rows in the main flow path; details of the internal flow structure within the bleed off-take cavities/ports are not discussed here.Copyright © 2005 by ASME

M. Goller

Papers

Numerical Investigation of Endwall Boundary Layer Removal on Highly-Loaded Axial Compressor Blade Rows