Effects of leading edge slat on flow separation and aerodynamic performance of wind turbine

Design and performance analysis of a two-stage transonic low-reaction counter-rotating aspirated fan/compressor with inlet counter-swirl

The effective control of the tip-leakage flow and loss is of great significance to improve the aerodynamic performance of the turbine. In this paper, the evolution mechanism of tip-leakage flow in a transonic high pressure turbine with a squealer tip is investigated with numerical simulation methods. The impacts of squealer geometric, such as the inclined pressure side rim and squealer rim width, on the vortex structure in the gap and tip-leakage loss are discussed. The results show that the scraping vortex inside the cavity plays the role of aero-labyrinth seal, and forms interlocking sealing labyrinth structure with the rims on both sides, which has an effective sealing effect on the tip-leakage flow. The inclined pressure side squealer rim inhibits the development of the pressure side squealer corner vortex, which is beneficial to expand the influence range of the scraping vortex and enhance the sealing effect on the tip-leakage flow. The increase of the suction side squealer rim width reduces the effective flow area at the gap exit, which is conducive to reduction of the tip-leakage flow rate and tip-leakage loss. However, the increase of the pressure side squealer rim width strengthens the pressure side squealer corner vortex and limits the development space of the scraping vortex, causing the adverse effects on the control of tip-leakage flow.

Effects of Squealer Geometry of Turbine Blade Tip on the Tip-Leakage Flow and Loss

The influence of diversified forward sweep heights on operating range and performance of an ultra-high-load low-reaction transonic compressor rotor

Influence of blade vibrations on aerodynamic performance of axial compressor in gas turbine: Direct numerical simulation

Design optimization of axial slot casing treatment in a highly-loaded mixed-flow compressor

Casing treatments (CT) can effectively extend compressors flow ranges with the expense of efficiency penalty. Compressor efficiency is closely linked to loss. Only revealing the mechanisms of loss generation can design a CT with high aerodynamic performance. In the paper, a highly-loaded mixed-flow compressor with tip clearance of 0.4 mm was numerically studied at a rotational speed of 30,000 r/min to reveal the effects of axial slot casing treatment (ASCT) on the loss mechanisms in the compressor. The results showed that both isentropic efficiency and stall margin were improved significantly by the ASCT. The local entropy generation method was used to analyze the loss mechanisms and to quantify the loss distributions in the blade passage. Based on the axial distributions of entropy generation rate, for both the cases with and without ASCT, the peak entropy generation rate increased in the rotor domain and decreased in the stator domain during throttling the compressor. The peak entropy generation in rotor was mainly caused by the tip leakage flow and flow separations near the rotor leading edge for the mixed-flow compressor no matter which casing was applied. The radial distributions of entropy generation rate showed that the reduction of loss in the rotor domain from 0.4 span to the rotor casing was the major reason for the efficiency improved by ASCT. The addition of ASCT exerted two opposite effects on the losses generated in the compressor. On the one hand, the intensity of tip leakage flow was weakened by the suction effect of slots, which alleviated the mixing effect between the tip leakage flow and main flow, and thus reduced the flow losses; On the other hand, the extra losses upstream the rotor leading edge were produced due to the shear effect and to the heat transfer. The aforementioned shear effect was caused by the different velocity magnitudes and directions, and the heat transfer was caused by temperature gradient between the injected flow and the incoming flow. For case with smooth casing (SC), 61.61% of the overall loss arose from tip leakage flow and casing boundary layer. When the ASCT was applied, that decreased to 55.34%. The loss generated by tip leakage flow and casing boundary layer decreased 20.54%) relatively by ASCT.

Entropy Generation Analysis in a Mixed-Flow Compressor with Casing Treatment

Performance enhancement of industrial high loaded gas compressor using Coanda jet flap

\n In order to survive in a complex environment, nature has produced efficient and versatile resource-rich structures. One of the novel drag reduction designs comes from the efficient movement of sharks through microscope riblets aligned along the flow direction. In this paper, the effectiveness of sharkskin-inspired riblets in reducing the aerodynamic loss of compressor cascade flow was investigated by using high-fidelity numerical simulation method. Two key normalized parameters were selected to parameterize various riblet designs, and the corresponding relative change in cascade performance was first investigated based on the uRANS simulations with/without transition model. Then, the large eddy simulations in conjunction with the wall-adapted local eddy viscosity model were conducted to investigate the cascade flow with the selected riblet design cases. By comparing the flow resistance, transition positions, vortex formations and turbulence fluctuations of the boundary flow, the flow control mechanisms of the riblets were finally studied. Simulation results show that compared with the prototype case, the total pressure loss can be reduced by up to 20.5% in the fully turbulent environment. This is because the spanwise fluctuation of the turbulent vortices is impeded, and the turbulent vortices are lifted above the riblet tip. Low-speed streaks inside the riblet valleys generate relatively low shear stresses, while the high-shear stresses occur only at the riblet tips. However, when considering transition from laminar to turbulent boundary flow, the aerodynamic performance of compressor cascade strongly depends on the riblet position relative to the transition on cascade SS. The total pressure loss can only be reduced by up to 8.1%, and even most riblet designs will degrade the cascade performance. The major reason is that the riblets are located upstream of the transition zone, especially at the small incidence angles. Due to the installation of riblets, the contact area between the laminar flow and the wall surface is increased, and the downstream laminar-to-turbulent transition is promoted.

Physical Mechanisms Investigation of Sharkskin-Inspired Compressor Cascade Based on Large Eddy Simulations


 A novel blowing flow control technique, called Coanda jet flap, to improve the performance of the highly loaded axial compressor is numerically and experimentally investigated in this study. A theoretical model is initially built to guide the preliminary design of the jet velocity. The design and effectiveness of the Coanda jet flap are then studied for two different blade designs: a highly-loaded double-arc blade cascade and a highly-loaded axial compressor stator. The optimal aerodynamic shape of the Coanda jet flap is achieved based on the genetic algorithm in conjunction with the artificial neural networks. A comparison of the flow details between the optimization result and the prototype is then conducted to understand the flow mechanisms responsible for the performance enhancement. The numerical and experimental results show that the Coanda jet effectively improves the aerodynamic performance of the highly loaded cascade. The total pressure loss is reduced by a maximum of 22.4% when the normalized mass flow rate of Coanda jet is equal to 1%. Meanwhile, the static pressure rise coefficient is increased by up to 14% with a 1.5% jet mass flow rate. The cantilevered stator vanes with Coanda jet flap is well-designed and embedded in a 1.5-stage highly loaded axial compressor stage. The numerical data shows that the total number of stator blades can be successfully reduced by 35% with the uncompromised overall performance when the Coanda jet flap is applied.

Zhihui Li

Papers

Design optimization of axial slot casing treatment in a highly-loaded mixed-flow compressor

Entropy Generation Analysis in a Mixed-Flow Compressor with Casing Treatment

Performance enhancement of industrial high loaded gas compressor using Coanda jet flap

Physical Mechanisms Investigation of Sharkskin-Inspired Compressor Cascade Based on Large Eddy Simulations

Improving Aerodynamic Performance of a Highly Loaded Compressor Based on Coanda Jet Flap