Xiaoqing Qiang

Analysis on slot-type casing treatment injection flow in an axial transonic compressor

The purpose of this work is to understand the properties of the injection flow through slots opening surfaces with steady and unsteady simulations. The feasibility of evaluating slot effectiveness by steady results is demonstrated. Transient features of injection flow are detailed investigated. Numerical investigations are carried out in a 1.5 axial transonic compressor stage at a specified rotating speed with seven kinds of slot-type casing treatments. Comparisons between steady/unsteady results show that differences of overall performance and injection mass flow rate are dependent on simulation methods, rather than slot configurations. Thus, correlation analysis by steady results of seven slot configurations is considered valid and reveals strong linear correlation between injection mass flow and stall margin improvements/efficiency drops. Therefore, it is practical to evaluate the effectiveness of a specific slot configuration in this compressor with steady results by calculating injection mass flow rate. Afterwards, unsteady simulations are performed with a specific configuration of arc-curve skewed slots. It is clarified that the dividing locations between suction/injection regions moves along the axial direction based on the relative rotor/slots location. Exchanging flow through slots opening surfaces displays periodic variations over time. The variation cycle for one single slot equals blade passing period T. For summation of mass flow through all slots, the cycle equals to T divided by slots number in one passage. The net flow rate through all opening surfaces is always less than zero during a blading passing period, i.e. injection mass flow rate is larger than suction flow all the time.

Development of an off-design deviation angle prediction model for full blade span in axial flow compressors

To reveal the deviation angle changing pattern in axial flow compressors, an off-design deviation angle prediction model for full blade span was developed through statistical analyses and analytical derivations. By studying the compressor test recordings collected from NASA open technical reports, a linear correlation between incidence and an implicit function of deviation angle was found from 5% to 95% span. An analytical method was introduced to predict the linear correlation through derivations of the implicit function. The derived results show good agreement with the regression values of the experimental data. The off-design deviation angle is predicted by decomposition of the derived linear correlation at full span. An experimental database with 21 different blades is used to validate the prediction model. Span range from 5% to 95% and incidence range from −25° to 22° are covered by the 1494 test points in the database. The prediction errors are smaller than 6° for all test points, 4° for 99% points, and 2° for 90% points in the database. The current method was also applied to the off-design deviation angle estimation of a low speed four-stage research compressor at full span in the numerical design phase. It shows the deviation angle cloud maps acquired from off-design 3D Reynolds-averaged Navier–Stokes simulations are consistent with the results calculated by the prediction model.

Effects of Vortex-Vortex Interaction in a Compressor Cascade With Vortex Generators

This paper presents a numerical investigation to explore the effects of vortex generators on a high speed compressor cascade. Secondary flow effects like the corner separation vortex have an influence on the performance of a compressor cascade such as leading to increased losses. In order to control the corner separation vortex and reduce losses, an extensive study of vortex generators applied to a compressor cascade is conducted. A preliminary study by steady 3D RANS simulations is performed using the Spalart-Allmaras turbulence model. The aerodynamic performance as well as the behavior of the corner separation vortex is investigated in the compressor cascade without vortex generators. Then, a vortex generator is added to the cascade, which is numerically simulated. Various configurations are considered, which are decided by the height and installation angle of the vortex generator. Comparison of the performance attained by these configurations results in an optimum scheme that has minimum losses. Furthermore, unsteady 3D DES simulations are performed with the optimum configuration. This method that predicts the flow field more precisely could help verify the accuracy of the RANS results. Finally, by analyzing all the resulting aerodynamic performance and numerical flow phenomena, the mechanism of vortex-vortex interaction is presented and discussed, which could be a criterion to reduce the corner separation flow and enhance the performance of axial compressors.Copyright

Investigation of Tip Leakage Flow and Stage Matching with Casing Treatment in a Transonic Mixed-Flow Compressor

Abstract The first stage of a transonic multi-stage mixed-flow compressor is numerically studied with and without casing treatment. First, overall performance and behavior of the tip leakage flow are investigated in the compressor stage with a smooth casing. Performance problems emerge in terms of narrow operating range and mismatching between rotor and stator. By investigating the flow field near tip region in detail, remarkable low momentum regions are observed at front and rear portion of rotor passage near suction surface, which grow up and extend further upstream along with mass flow reduced to near stall point, which contributes to a narrow stall margin. Detailed analysis indicates that tip leakage vortex and two types of leakage flow with different flow behaviors are main causes of low momentum regions. Shock-leakage flow interaction and vortex breakdown play an important role in formation of these regions. To improve the flow field near the rotor tip and extend the stable operating range, a circumferential groove casing treatment is then adopted, starting from 10% and ending at 94% axial chord. As expected, the low momentum regions are largely diminished by the casing treatment and stall margin of the investigated compressor stage is effectively enhanced. Fluid from circumferential grooves is injected into blade passage near the suction surface and re-energizes the leakage flow, which makes mainly contribution to manipulation of tip leakage flow and stall margin improvement. Since the pressure difference across blade tip section has a great impact on effectiveness of circumferential grooves, the positions of shock wave and tip leakage flow as well as where the interaction takes place ought to be taken into account through the casing treatment design procedure.

Effect of Casing Suction on Stage Matching and Flow Loss in a High Pressure Axial Compressor

Abstract A numerical simulation of a 1.5 stages high pressure axial compressor is presented. The effect of casing suction on compressor aerodynamic performance, stage matching as well as flow loss is discussed in detail. Using modern CFD codes Numeca/FINE, the 3D steady flow inside the 1.5 stages axial compressor has been simulated and visualized, respectively at cruise speed and maximum climbing speed. Numerical solutions show that casing suction partly removes the low-momentum fluid and reduces the flow blockage at tip region, thus improves stage matching mildly between rotor and stator. In general, casing suction, which provides main flow for flight air system, has slight impact on compressor blade row performance and loss characteristics.