Flow And Heat Transfer Characteristics Of Micro Pin-Fins Under Jet Impingement Array

In order to achieve higher cycle efficiency and ultra-low pollution emissions,the inlet temperature of gas turbine is rising,which is far higher than the metal tolerance temperature.It is urgent to explore a more efficient cooling technique.The micro pin-fin has the potential to enhance convective heat transfer at the cost of little flow loss,so it gradually becomes a direction of the next generation of cooling technology.Because it mainly acts near the flow boundary layer and thermal boundary layer,there are many geometrical and flow parameters affecting the convective heat transfer characteristics of the cooling structure,and the law is complex,so exploring the mechanism of heat transfer enhancement by micro pin-fin is of great significance for the development of new generation cooling technology.In terms of experimental methods,an internal cooling test bench for micro pin-fin in a suction wind tunnel which can accurately control the inlet flow temperature and flow rate was established.A high precision temperature control system and heat flux measurement system based on PI control system were built,and a steady measurement method for micro pin-fin based on lumped parameter method was developed.The experimental measurement system of micro pin-fin has the ability of accurately controlling external environment variables,rapidly reaching steady state,synchronously measuring temperature and heat flux,and high measurement accuracy.According to the characteristics of actual gas turbine cooling and micro pin-fin,a typical structure of array impingement cooling with micro pin-fin is derived in this paper.Based on the experimental measurement system,the effects of jet impingement distances,shapes of micro pin-fin,heights of micro pin-fin and Reynolds number on the heat transfer characteristics of the new cooling configuration were systematically studied under 10 sets of geometry and 30 sets of conditions.The results show that the micro pin-fin can enhance the average heat transfer enhancement up to 30%?120%,and the discharge coefficient is basically unchanged.it has the ability to achieve higher heat transfer at the cost of small pressure loss.The area-averaged Nusselt number ratio increases with the increase of micro pin-fin heights,which is a key parameter.Aiming at the experimental conditions,a semi-automatic numerical calculation process based on RANS is adopted to carry out batch calculation.The numerical results are consistent with the experimental results qualitatively and quantitatively,which verifies the validity of the numerical method.The numerical results show that the pressure loss at the hole position is dominant in the total pressure loss for the 3-D jet to target distance cooling structure,which means that the increase of pressure loss after the micro pin-fin placed on the target surface has little effect on the total pressure loss,and reveals the mechanism of the micro pin-fin array resulting in little pressure loss.It is pointed out that the heat transfer enhancement mechanism of the micro pin-fin is that the micro pin-fin increases the velocity of u near the wall and enhances the heat transfer.The results show that the micro pin-fins under jet impingement array has the ability to enhance convective heat transfer at the cost of little flow loss.With the development of additive manufacturing technology,the micro pin-fins cooling technology will become an advanced cooling technology with great potential,supporting the design of next-generation gas turbine cooling technology.