| Micro gas turbine has a series of advantages such as small size,light weight,low noise and low cost,which is widely used in aviation,distributed energy,petroleum,railway and shipbuilding industries.In order to improve the efficiency of micro gas turbine,the method of increasing turbine inlet temperature is usually used.However,due to the constraints of space size and reliability,it has been the focus and difficulty in the field of micro gas turbine research to cool the radial turbine and improve its pre vortex temperature.Based on this,this paper puts forward the back plate impingement cooling technology of the radial turbine,and studies the cooling characteristics of the back plate of the radial turbine by using the numerical simulation method of gas thermal coupling.The research content mainly includes the following two aspects:first,the basic research on the jet impingement cooling structure of the back plate of the runoff turbine without volute is carried out through the numerical simulation,and the research content is the influence law of the aerodynamic parameters and geometric parameters on the flow and heat transfer characteristics.The main aerodynamic parameters include:cooling flow and cooling temperature;the main geometric parameters include:pre selection angle of jet holes,number of jet holes and distance between back plates;the second is that the back plate jet impingement cooling structure is adopted in the runoff turbine with volute,and the following two factors affecting jet cooling are analyzed.The first is the influence of volute shape on impingement cooling effect;the second is to change jet flow;According to calculate result,the main conclusions are as follows:1.The parts with large heat load of runoff turbine are mainly located in the back plate and blade tip of turbine.The new back plate impact cooling technology has obvious influence on the cooling effect of the two areas,especially in the high-level area with large heat load of back plate.In the simplified volute free runoff turbine model,with the increase of cooling temperature,the cooling effect of back plate becomes worse.When the cooling gas temperature is fixed,the relative flow of cooling gas increases from 1%to 4%.Compared with the original without cooling,the average temperature of back plate decreases by 150k-252k.2.Among the five pre selected angles,the cooling effect is the best when the prerotation angle is ?=60°.The larger the pre rotation angle is,the worse the cooling effect is.Increasing the number of jet holes can improve the uniformity of cooling efficiency distribution and the average cooling efficiency.When the distance between the impact holes increases,the impact pressure on the surface of the back plate decreases,and the heat transfer effect of the impact cooling decreases.At this time,the convection heat transfer effect on the target surface is strengthened.In the calculation range of this paper,the back plate cooling effect is the best when the distance between the impact holes is 1.0mm.3.The uneven circumferential flow field caused by the volute can cause thedistortion of the distribution of the cooling efficiency of the turbine back plate.In the area with high volute pressure,the cooling fluid is difficult to flow out due to the suppression of the main stream,and the cooling efficiency is low;in the area with low pressure,the cooling fluid is easy to flow out,which may further enhance the effect of local heat exchange.By optimizing the different phase angles of the uniform distribution scheme of jet holes,the uniformity of cooling effect near the vortex tongue is improved to some extent,but the improvement effect is small;however,by adding jet holes near the vortex tongue,the minimum cooling efficiency and the maximum cooling efficiency of the turbine back plate are 14.9%and 4.1%higher than that of the uniform distribution scheme,and the uniformity of cooling effect is 17.9%higher than that of the uniform distribution scheme. |
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