Investigation Of Film-hole Entrance Effects On Film Cooling Performance

This paper investigated the entrance effects on flow field and adiabatic film cooling effectiveness,which caused by the orientation of the secondary flow.The main research contents and conclusions are summarized as the followings:Firstly,aiming at the validation of numerical simulations,experimental tests on the cylindrical-hole film cooling with internal crossflow on a flat plate are carried out in advance.The results show that numerical results are in general agreements with the corresponding experimental results.Secondly,numerical simulations are performed to investigate the the entrance effects on the film cooling performance on a flat plate.Two kinds of holes(cylindrical hole and fan-shaped hole)and four types of coolant-fed modes(plenum,inline,counter and crossflow)are considered.The results show that,the orientation of the secondary flow affects the internal flow field inside the film cooling hole and mutual interaction of the coolant jet and the primary flow.The increase in the length-to-diameter ratio of film cooling hole or the crossflow-to-coolant jet velocity ratio promotes the lift-off of the coolant jet,and causes the coolant to detach from the film-cooled surface.Under the crossflow coolant-fed mode,the direction of the outflow from the fan-shaped hole is opposite to that from the cylindrical hole under the same working condition.In general,the orientation of the secondary flow has a great influence on the adiabatic film cooling effectiveness for the cylindrical film cooling hole.In the situations of low length-to-diameter ratio and low crossflow-to-coolant jet velocity ratio,the inline and crossflow coolant-fed modes show favorable influence on improving the film cooling effectiveness when compared to the plenum or baseline coolant-fed mode.For the fan-shaped film cooling hole,the inline coolant-fed mode shows a certain positive role on improving film cooling effectiveness under a low length-to-diameter ratio,a low crossflow-to-coolant jet velocity ratio and a high blow ratio.The discharge coefficient of the cylindrical hole decreases with the increase of film-hole length-to-diameter ratio or crossflow-to-coolant jet velocity ratio.The discharge coefficient of the fan-shaped hole increases with the increase of the length-to-diameter ratio.At high blow ratios,both the inline and the counter coolant-fed modes decrease the discharge coefficientat in comparison with the plenum coolant-fed mode.Finally,a series of numerical simualations are performed to study the internal crossflow effect on single-row film cooling performances on the suction and pressure sides of a turbine guide vane.The results show that,the helical flow feature is dominant inside film cooling hole in the presence of internal crossflow.At the suction side,the ejection jet is pushed toward one side in accordance to the internal flow direction.But the situation at the pressure side is opposite.At the suction side,when the crossflow-to-coolant jet velocity ratio is increased to Vr=2.0,the discharge coefficient of cylindrical or fan-shaped hole decreases obviously.At the pressure side,the influence of crossflow on the discharge coefficient behaves more significantly.The discharge coefficient decreases with the increase of the crossflow-to-coolant jet velocity ratio.At the suction side,a smaller crossflow-to-coolant jet velocity ratio may improve the laterally-averaged adiabatic film cooling effectiveness under high blowing ratios but a higher crossflow-to-coolant jet velocity ratio produces an opposite influence.At the pressure side,the crossflow effect is generally favourable to improve the adiabatic film cooling effectiveness of the cylindrical hole.However,for the fan-shaped film cooling hole,the crossflow effect produces an adverse effect on the adiabatic film cooling effectiveness under high blowing ratios.