Investigation For Effect Of Wall Thickness On Film-cooling Performance On Plate

Film-cooling is an effective method applied to cooling high-temperature components of aero engine.Wall thickness affects the length of the film hole and the coolant flow within the hole,therefore,the film cooling performance is affected by the wall thickness.Most of the researchers maintain the temperature ratio between the coolant and mainstream gas being close to 1 in the basic investigation,whereas,the temperature ratio is close to 2 under the real environment of engine,resulting in difference of the aerodynamic parameters effecting on the film cooling performance.In order to investigation the influence of wall thickness and the temperature ratio on film cooling performance,numerical simulation was carried out to investigate the flow field,the temperature field and the cooling effectiveness when the cooled wall thickness was one times,two times and three times diameter of the film-cooling hole and the temperature ratio was 1.2、1.5 and 2.0.The result of exploring the influence of wall thickness on film cooling performance show that high-speed region appear at the hole with the wall thickness of one times of the hole diameter,resulting in increasing the jet momentum and promoting the coolant lifted off the wall.The lateral velocity of coolant is towards to the center line of hole,resulting in weakening spanwise diffusion.Compared with the wall thickness of three times of hole diameter,the values of spanwise averaged film cooling effectiveness for one times of hole diameter are lower 9% ~ 45%,21%~ 43% and 9%~62% at the ratios of 1.0,1.5 and 2.0,respectively.There is little difference for spanwise averaged film cooling effectiveness between the wall thickness of two times and three times of hole diameter.As blowing ratio increases,film cooling effectiveness difference resulting from wall thickness decreases nearby outlet of film hole.The mixing between coolant and main fluid decreases the fluid velocity nearby the wall,resulting in decreasing the friction heat in compressible flow film cooling with large flow velocity.The result of exploring the influence of temperature ratio between coolant and main fluid on film cooling performance show that as the temperature ratio decreases,the pressure ratio at the film hole exit and inside hole decreases,resulting in increasing the velocity within the hole and at the hole outlet.The dimensionless temperature and density at the exit of hole decrease with decreasing temperature ratio.It is contribute to suppression of jet separation when the temperature ratio is 2.0.When the blowing ratio is 1.0,the spanwise averaged cooling effectiveness decreases with the decreasing of the temperature ratio,and compared with the temperature ratio of 2.0,the spanwise averaged cooling effectiveness are lower 9.3%~ 24.1% and 13.4% ~ 30.8% for the temperature ratio of 1.5 and 1.2 respectively.Spanwise averaged film cooling effectiveness of temperature ratio of 1.2 higher than temperature ratio of 1.5,but they are both lower 10.9% ~ 22.5% and 20.5% ~ 27.8% respectively than temperature ratio of 2.0,at the brow ratio of 1.5.When the blowing ratio is 2.0,spanwise averaged film cooling effectiveness of temperature ratio of 1.2 is the highest of all temperature ratio,it is higher 6% ~19.7% and 15.1% ~ 23.6% respectively than the temperature ratio of 2.0 and 1.5.