Abstract
In the present study, a numerical simulation was conducted to investigate the influence of surface roughness on the aerodynamic performance of a 1.5-stage highly loaded axial compressor at low Reynolds number. It was especially considered how the roughness Reynolds number ( k + ) affected the change of the inlet and outlet conditions, the growth of the separation bubble (LSB), the status of the limiting streamline, and the patterns of the wake. Regarding the roughness settings, five roughness magnitudes and four roughness locations were mainly studied. The results showed that at low Re, surface roughness mainly improved the stage performance by reducing the length and width of the LSB as well as the rotor tip vorticity, delaying the occurrence of three-dimensional flow separation and increasing the turbulence level near the wall. However, it also aggravated the incoordination between the subsequent stages to a certain extent, which limited further improvement of the overall aerodynamic performance. Generally, with k + increasing, the compressor aerodynamic performance improved and achieved the best at k + = 137.8 . The maximum increases in the total pressure ratio, peak efficiency, and chocked mass flow were approximately 4.01%, 5.34%, and 2.24%, respectively. In addition, for all the four roughness locations, the roughness covering from the leading edge to 50% of the axial chord length on the suction surface had a relatively evident advantage in improving the compressor peak efficiency because of the better control of the LSB and wall shear stress.
Highlights
When an unmanned aerial vehicle (UAV) cruises at high altitudes, the Reynolds number (Re) based on the blade chord decreased sharply, which seriously affects the separation, transition, and other flow conditions of the compressor blade surface [1, 2]
The surface roughness control method was effective in controlling boundary layer development and improving the compressor aerodynamic performance at low Re without imposing additional complex geometric shapes on the blade
This paper concentrated on the influences of roughness magnitudes (k+) and locations (25%-SS, 50%-SS, 75%-SS, and 100%-SS) on the aerodynamic performance of a smallscale 1.5-stage highly loaded transonic axial compressor under 20-km altitude conditions (Re = 4:5 × 104) by using a commercial CFD code
Summary
When an unmanned aerial vehicle (UAV) cruises at high altitudes, the Reynolds number (Re) based on the blade chord decreased sharply, which seriously affects the separation, transition, and other flow conditions of the compressor blade surface [1, 2]. In order to further investigate and analyze the phenomenon and mechanism of the flow separation and transition on the turbomachinery blade surface at low Reynolds number and to improve the aerodynamic characteristics, scholars have adopted several active or passive techniques, including utilizing a flexible membrane [5], blade surface layer suction [6], casing treatments [7], pulsed vortex generator jets [8, 9], and surface roughness control [10]. In the past few decades, the influence of blade surface roughness on the aerodynamic performance of a compressor has become a hot research
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