Haixin Chen

CFD Investigation on the Circumferential Grooves Casing Treatment of Transonic Compressor

The performance of NASA Rotor 37 with Circumferential Grooves Casing Treatment (CGCT) is studied with an in-house CFD code NSAWET. Based on the stall mechanism analysis, a number of CGCT configurations have been proposed and numerically tested. The computation results show that the stall mechanisms are strongly related with the width of tip clearance. With a small tip clearance, the stall process is dominated by the trailing edge separation, while the leading edge tip leakage vortex breakdown induced blockage causes stall in a large tip clearance configuration. Circumferential grooves at appropriate axial locations can be beneficial to the stall margin in these two types of stall processes. The effects of the groove width and depth are presented. The mechanisms of CGCT for different tip clearances are also discussed.Copyright

A Computational Fluid Dynamics Study of Circumferential Groove Casing Treatment in a Transonic Axial Compressor

Numerical investigations were conducted to predict the performance of a transonic axial compressor rotor with circumferential groove casing treatment. The Notre Dame Transonic Axial Compressor (ND-TAC) was simulated at Tsinghua University with an in-house computational fluid dynamics (CFD) code (NSAWET) for this work. Experimental data from the ND-TAC were used to define the geometry, boundary conditions, and data sampling method for the numerical simulation. These efforts, combined with several unique simulation approaches, such as nonmatched grid boundary technology to treat the periodic boundaries and interfaces between groove grids and the passage grid, resulted in good agreement between the numerical and experimental results for overall compressor performance and radial profiles of exit total pressure. Efforts were made to study blade level flow mechanisms to determine how the casing treatment impacts the compressors stall margin and performance. The flow structures in the passage, the tip gap, and the grooves as well as their mutual interactions were plotted and analyzed. The flow and momentum transport across the tip gap in the smooth wall and the casing treatment configurations were quantitatively compared.

A CFD Study of Circumferential Groove Casing Treatments in a Transonic Axial Compressor

Numerical investigations were conducted to predict the performance of a transonic axial compressor rotor with circumferential groove casing treatment. The Notre Dame Transonic Axial Compressor (ND-TAC) was simulated by Tsinghua University with an in-house CFD code (NSAWET) for this work. Experimental data from the ND-TAC were used to define the geometry, boundary conditions and data sampling method for the numerical simulation. These efforts, combined with several unique simulation approaches, such as non-matched grid boundary technology to treat the periodic boundaries and interfaces between groove grids and the passage grid, resulted in good agreement between the numerical and experimental results for overall compressor performance and radial profiles of exit total pressure. Efforts were made to study blade level flow mechanisms to determine how the casing treatment impacts the compressor’s stall margin and performance. The flow structures in the passage, the tip gap and the grooves as well as their mutual interactions were plotted and analyzed. The flow and momentum transport across the tip gap in the smooth wall and the casing treatment configurations were quantitatively compared.Copyright

Investigation of the Influence of Hub Gap Size to the Performance of a Subsonic Compressor Stator

This paper presents a RANS study of the hub clearance effects on the performance of a subsonic compressor stator. The inlet boundary conditions are from the calculation of inlet guide vanes. The k-ω SST turbulence model is adapted to resolve the Reynolds stresses. The present numerical results are compared with the experiment carried out at Technical University Berlin. The circumferentially averaged total pressure has a strong decrease in the lower span region from hub to nearly 50% channel height, while the tangential flow angle reduces from approximately 40% channel height to the hub, linearly. The above phenomenon indicates that the leakage flow in the gap between stator blade and the hub does not turn sufficiently. This leads to a smaller incidence angle of the flow to the stator, thus, the lower span of the stator works in smaller attack angle, 0 to 13 degrees lower than the higher span. Surface flow patterns on the hub and both side of the blade surfaces are compared with the oil flow visualization in the experiment. The compressor stator is shown to operate under large separation and strong back flow conditions. The hub leakage flow is studied together with the endwall flow phenomenon for full gap configuration. Two separation lines are observed on the hub. One is lying in front of the blade leading edge plane indicating the separation due to the leading edge leakage flow which spills out of the passage before the flow enters the passage. The other is caused by the interaction between the strong hub leakage flow and the incoming flow. This separation line undergoes an abrupt turning just after the flow leaving the stator passage. The effect of the hub gap size on the leakage flow and the whole flow passage in the stator, including the strength and location of the vortex structure, the location and size of the separation bubble, as well as the back flow behavior, is analyzed. With the help of a novel vortex identification method, the flow field of this subsonic compressor stator and the inlet guide vanes can be visualized illustrating the behavior at the operation point when rotating instability occurs. The parameter η4 can help identifying the stretching and relaxation of the vortex. This approach reveals significant flow details [1]. Combined with DPH (Dynamic Pressure Head) contour and streamlines, the detailed vortices structures and topology in a subsonic compressor can also be further elucidated. The study illustrates different vortices structures in the compressor, as well as their behavior in different gap size configurations.Copyright

Axial Compressor Stall, Circumferential Groove Casing Treatment, and the Tip-Clearance Momentum Flux

The stall margin and pressure ratio of an axial compressor can both be increased with the use of circumferential groove casing treatments over the rotor. Performance and stall point measurements were obtained in a single-stage high-speed axial compressor with seven different casing treatment configurations. The different configurations were designed to investigate the effects of the number and placement of circumferential grooves. The results demonstrated that the stall margin extension caused by individual grooves could be added together to obtain the value obtained with the equivalent multigroove configuration. Furthermore, the relationship between stall margin extension and the tip-clearance momentum flux was considered. A Reynolds-averaged Navier–Stokes computational solution from the smooth-wall configuration was used to obtain the momentum flux of the reverse flow at the tip. The results showed a linear relationship between the measured stall extension and the computed smooth-wall momentum flux inte...