Experimental Study Of Surface Roughness Effects On Compressor Cascade Performance

During long-term operation, the performance parameters of gas turbines gradually decrease, which directly affects the operation and maintenance costs. How to maintain the gas turbines in a relatively high-efficient operating state is a problem concerned by both gas turbine manufacturers and users. Among the many factors, the main causes of compressor blade performance degradation can be attributed to fouling, erosion and corrosion. Although the modes and causes of compressor blade performance degradation are different, they all result in an increase in blade surface roughness. The surface roughness can be equivalent to a perturbation imposed on the fluids around the blade surface, and the influence is related to the intensity and location of the disturbance and flow field conditions. Thus, the investigations of roughness magnitudes, locations and inflow conditions have always been the focus of the researches on roughness impacts. But due to different design parameters and operating conditions of compressor blades, many research conclusions of roughness effects are not universal up to now. In particular, most of the experimental studies on cascade roughness are at a certain incidence angle, the understanding of roughness magnitudes and locations impacts at different incidence angles is not clear yet. Therefore, to address the problem of different extent performance degradations of actual blades, in this paper, the method of low-speed compressor planar cascade experiments is chosen to carry out the following studies:1. Impact of blade thickness increase on the cascade performanceCompared to the roughness classes of mechanical finishing, the 7000 # sandpaper was selected in the experiments to quantitatively investigate the effects of blade thickness variation induced by sticking sandpapers on the cascade total pressure loss-incidence angles characteristics, loads and flow turning angles with the aid of numerical methods. The trends of blade thickening impacts on cascade performance at different incidence angles and their causes were analyzed. The influence of the blade thickness increase magnitude caused by actual compressor fouling on the airfoil in this paper was discussed. Meanwhile, the analysis of the thickened blade performance provided a basis through the roughness studies.2. Impact of different roughness magnitudes on the cascade performanceFour kinds of sandpapers were selected to study the effects of different roughness magnitudes on the cascade total pressure loss-incidence angles characteristics and flow turning angles, referred to the related criteria’s of roughness impacts. The baseline of the comparison was the thickened smooth blade in the thickness analysis. The sensitive region of roughness magnitudes was approximately defined. The changes of sensitive region with inflow Re numbers and incidence angles were discussed. The differences among the impact trends and degrees of roughness magnitudes on the cascade performance within various incidence angle regions were analyzed. Meanwhile, preliminary discussions were carried out on the reduction of total pressure loss induced by roughness at low Re number.3. Impact of different roughness locations on the cascade performanceThe roughness magnitude of 80 μm was selected to study the effects of different roughness locations on the cascade total pressure loss-incidence angles characteristics and flow turning angles. The baseline of the comparison was the thickened smooth blade in the thickness analysis. The relationship between the impacts of roughness locations and incidence angles was analyzed. The sensitive roughness locations of this blade were approximately defined. The differences among the impact trends and degrees of sensitive roughness locations on the cascade performance at various Re numbers and incidence angles were discussed and preliminary mechanism analysis was made with the aid of numerical method.