Flow And Heat Transfer Characteristics In The Confined Passage With Impingement Cooling And Swirl Cooling

High turbine inlet temperature in modern gas turbine engines requires propercooling techniques to protect it from overheat. Among all of the heat transferenhancement techniques, jet impingement has the most significant potential toincrease the local heat-transfer coefficient. Recent development in casting technologyhas allowed very intricate internal passage to be manufactured. This has opened upthe possibility of casting small diameter different geometry impingement passage intoturbine blades. The jet air, after impingement, is constrained to flow along the channelformed between the orifice plate and the inner surface of the airfoil envelope, releasesfrom the film cooling holes or enters other chamber. Strong swirl can be induced inthe passage by the jets. It is expected that the cooling effect in such passage would beincreased by an optimize combination of impingement cooling, swirl cooling and filmcooling. In order to gain greater in-sight into the flow structure of confined passage,get detail knowledge of heat transfer characteristic on the passage inner surface,experimental and numerical investigations of aerodynamic aspects and heat transfercharacteristic were carried out in large scaled test models.Two test models with trapezoid cross section were built up in the experiment, onefor flow field measurements and the other for the heat transfer measurements. On oneside of the passage, the air entered in from a row of 40 staggered arrangementimpingement holes. A row of 25 exit holes was opened on the opposite side to theimpingement orifice plate. There were three rows of film cooling holes withcompound angle on the bottom wall of the passage, each row contained 15 holes. Aneven larger outlet hole could be found in one end wall of the passage. The geometryof heat transfer measurements model was same as that of the flow field measurementsone, but the length of the passage was shortened about 40 percent and the film coolingholes were canceled. In both flow field measurements model and heat transfermeasurements models, the impingement angle of 35°and 45°were considered. Therange of Re number for flow field measurements was 15000 to 30000, while theoutflow flux ratio of the outlet hole varied as 0.25 and 0.5. For the heat transfermeasurements model, the range of Re number and the outflow flux ratio of the outlethole were 10000 to 40000 and 0 to 0.5 respectively.Parts of the experimental and numerical results were presented in the thesis. The influences of impingement angle, outflow flux ratio and Re number on both flowfields and heat transfer were detailed investigated. The major conclusions of this studyare shown as following:1. A strong swirl was found in the trapeziform passage. The smaller jets impingedeffectively on the bottom wall, while the larger jets mostly devoted into the swirl.Strong interaction effect existed between the smaller and larger jets.2. Crossflow was formed in the passage by the out flow at the end of the passage.In the downstream region, the jets were deflected by the crossflow, and the intensityof swirl was augmented. The increasing of crossflow intensity leaded to reverse flowin the exit hole, and the Nu numbers on bottom wall were reduced rapidly when thatof the exit side wall affected slightly.3. Smaller impingement angle could increase the swirl intensity and decrease theflow loss of the exit hole, when larger impingement angle increased the resistanceability of the jets on the crossflow effect and enhanced local Nu number on the bottomwall.4. Re number had no obvious effect on the flow structure of the passage and exithole, but played primary role on the Nu number of bottom wall and side wall. Theheat transfer was augmented distinctly with Re number increasing.5. The location and mass flux of film cooling holes had little effect on the flowstructure, but would affect the discharge coefficient of film cooling hole. Thedischarge coefficients of the impingement holes and exit holes decreased with theincreasing of crossflow intensity.6. In the studied cooling configuration, the level of heat transfer enhancement byswirl flow could approach, and even exceed the level of impingement cooling.Compared with the smooth pipe flow, the Nu number were augmented about 200 to300 percent on the bottom wall and side wall.7. The numerical results reveal the details of the flow patterns in the passage. Theconsistency of the numerical simulation and experiments are well in most of themeasured domains. Yet some differences still appear in some zones, which could beameliorated by the improved turbulence model and wall function.