Research On Film Cooling Of Sinusoidal Corrugated Wall

Longitudinal ripple heat shield is widely applied in military aero-engine afterburner thermalprotection, in which sinusoidal corrugated wall is distributed periodically along the flow direction. Inthis paper, film cooling of sinusoidal corrugated wall wasinvestigated systematically for the firsttimeby the means of combining numerical simulation with experimental study.Firstly, film cooling characteristics of the sinusoidal corrugated wall were studied by numericalsimulation. This part of research included the following contents:The flow characteristics ofmainstream near sinusoidal corrugated wall without cooling jets’ flow; The influence of hole position,blowing ratio and staggering rows of holes on flow field structure of a ripple cycle after hole and filmcooling effectiveness with cooling jets’ flow. The results have showed that: without cooling jets’ flow,two-dimensional boundary layer separation occurs after the wave crest and brings out span-wisevortex near the trough in larger scale, which is one of the typical differences between sinusoidalcorrugated wall and other geometric surface film cooling; With cooling jets’flow, boundary layerseparation turns to three-dimensional separation. Separation zone scale directly affects film coolingefficiency and span-wise distribution uniformity;Hole position and blowing ratio affect the shape ofthe separation votex and separation zone scale respectively;Staggering rows of holes enhances theefficiency of film cooling obviously.Secondly, according to staggering rows of holes, application of Seller film cooling efficiencysuperposition formula on sinusoidal corrugated wall film cooling was investigated by means ofnumerical simulation. It has proved the applicability of the formula, showed the essential reason ofsuperposition error, and brought up a method of reducing error.In addition, discrete-hole film cooling efficiency and film heat transfer coefficient in differentrowswere measured in a cycle of sinusoidalwavy wall along the flow direction by experimentalmethod. This paper also discussed effects of row number of holes, hole position, blowing ratio andmain flow Reynolds number; Calculation under the experimental conditions was carried out toinvestigate film cooling characteristics, and further to reveal the details of the flow field, used toexplain the experimentally obtained relevant laws.The results have showed that: under a certainblowing ratio condition, film cooling efficiency in different row number of holes appears obviouscorrugated distribution. The maximum and minimum values of film cooling efficiency are seen in thecorrugated back to mainstream flow side and a corrugated face the mainstream flow side,this is one of the unique characteristics in sinusoidal corrugated wall film cooling; The discrease in the row numberof holes and and increase of blowing ratio will weaken corrugated distribution characteristics of filmcooling efficiency; When blowing ratio is less than0.6, opening holes at the wave trough anddownstream location close to the trough will cause the backing-flow phenomena of main flow andgreatly aggravate local and downstream wall film cooling effectiveness, therefore it should be avoidedin engineering design; Film heat transfer coefficient of sinusoidal corrugated wall also presentscorrugated distribution characteristics, and in the fewer number of rows is especially obvious, themaximum and the minimum values occur near the wave crest and trough; mainstream Reynoldsnumber has a significant effect on film heat transfer coefficient, while blowing ratio does little.Furthermore, by the method of numerical simulation, application of full-coverge film cooling insinusoidal corrugated wall was studied. The main research contents have included: The difference offlow characteristics between discrete-hole film cooling and full-coverage film cooling, and effect ofwhich on film cooling efficiency;The effect of non-dimensional hole diameter, porosity, spacing ratioand blowing ratio on full-coverage film cooling flow field of sinusoidal corrugated wall and filmcooling efficiency.The results have showed that: by increasing the contact area of jet flow andmainstream boundary layer near the wall,full-coverage fllm holes increase the injection attenuationrate, reduce the penetration degree of jet on the mainstream boundary layer near wall, and enhancewall film cooling efficiency. This is the largest internal technical difference between full film coolingand discrete film cooling;Reducing hole diameter, increasing porosity,and reducing spacing ratio willenhance film cooling efficiency, but the effect of spacing ratiois weakerr compared to influence ofhole diameter and porosity.Finally, the impact of mainstream Reynolds number, blowing ratio, inlet streamwise turbulentintensityof main streamand local porosity changes were investigated in full-coverage film cooling ofsinusoidal corrugated wall by the means of experiment.The results have showed that: At the initialstage, averaged film cooling effectiveness distribution of sinusoidal corrugated wall is relatively flat.As blowing ratio increases, the whole film cooling efficiency increases slightly; average span-wisefilm heat transfer coefficient distribution has certain corrugated features; The enhancing effect ofmainstream Reynolds number on film heat transfer coefficient is obviously weaker than discrete-holefilm cooling case, which is one of the typical characteristics of full film cooling; Reducing porosity ofwall departing from the main flow direction will significantly weaken corrugated distribution featuresof averaged span-wise film cooling effectiveness; Only when turbulent intensity is larger than10%,its influence on full film cooling characteristics in the sinusoidal corrugated wall appeared gradually, mainly on weakening the efficiency of film cooling and lifting film heat transfer coefficient.Inaddition, this paper studied the effect of surface curvature on the infrared temperature measurementaccuracy from the point of infrared temperature measurement for the first time, this paper points outthat the direction of infrared temperature measurement and curvature of measured surface are themain reason affecting the infrared temperature measurement accuracy, and brings up the method ofmodifying the direction error of infrared temperature measurement.