Abstract
Gurney flap is a miniature lift-enhancement device installed at the airfoil trailing edge and has been successfully applied to fixed wing aircraft and low-speed horizontal wind turbines. In this article, Gurney flap is extended to increase pressure output of a diffusive cascade flow in rotating turbomachinery, which is complicated for its three dimensionalities and diffusive separation characteristics. Wind tunnel tests and computational fluid dynamic simulations were accomplished on an axial fan profiled with an NACA 65-(12)10 airfoil to investigate the effects of Gurney flap on the performance of a high solidity. We present the detailed flow features of the fan with and without Gurney flap after validating the simulation results with the experimental datum. The experimental results show positive Gurney flap effects on fan’s pressure rise and flow rate improvement. However, negative Gurney flap effects on fan’s efficiency are more evident than Gurney flap on isolated airfoils. Detailed flow field analysis from computational fluid dynamic computation reveals that the increased airfoil pressure loading along the fan blade chord strengthens the tip leakage flow, which induces more tip second flow losses than in the baseline fan. In addition to the positive lift enhancement, the net Gurney flap effect in diffusion cascade is influenced by the three-dimensional flow structure.
Highlights
Gurney flap (GF) was invented by a race car driver Dan Gurney in 1960
Beyond a velocity of 10 m/s, the variation in the total pressure and static pressure field is less than 0.1% and 0.3%, respectively, while the maximum deflection of the flow angle is below 6 0.2 degree, and the turbulence intensity is less than 0.5% in the test section
The operation range, which is designed by flow rate coefficient q, is 0.25–0.40
Summary
Gurney flap (GF) was invented by a race car driver Dan Gurney in 1960. It is a small lift-enhancement device which is usually mounted close to or at the airfoil trailing edge. Xie et al.[10] utilized a new type of GF on NACA0012 airfoil, which showed significant increase in energy extraction coefficient and efficiency They found an alternatively shed Karman vortex street behind the airfoil, which reduces the adverse pressure gradient near the trailing edge and increases the velocity over the suction surface, resulting in a delay in flow separation and decrease of pressure over there. Numerical studies have been carried out on the effectiveness of trailing-edge GF with varying depth and spanwise length on an axial compressor rotor by Mudassir and Quamber.[25] The results showed that high blade loading with GF was responsible for lower stall margin. The application of GFs seems to be a promising approach to improve the performance of axial fans since fan blade sections are similar lift generating device as airfoils. CFD results give insights of flow control mechanism and a theoretical foundation for further application optimization on axial fans
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