Flow Characteristics In The Short Channel With Staggered Impinging Jets Arrangement

In order to protect the high temperature components (turbine blades for example) and prolong the life of high performance aero-engines advanced cooling technologies must be applied. Among all of the cooling technologies, the impingement cooling is the most potential one to enhance local heat transfer coefficient. The impingement of the jet forms high speed airflows on the cooled surface. These airflows can be used to improve local heat-transfer conditions significantly especially in the area with very high heat flux and temperature. This thesis describes the experimental and numerical researches of the flow characteristics of the impingement cooling in confined passages.The experimental models are two rectangular channels with different geometry parameters. There are three stagger impinging holes and a outlet-hole on the top wall of the channels. Flow fields in the jet holes, passage and exit hole were measured with five hole probes. Pressure distributions along the channel were measured on the side wall and exit of the jet holes. Discharge coefficients of the jet hole and exit hole were obtained. The effects of the variations of Reynolds number (based on the diameter the jet velocity in the most upstream jet hole), height/jet hole diameter ratio, space between the jet holes on the flow fields and discharge coefficients were studied. Numerical simulations were carried out with FLUENT 6.0. It provided the details of the investigated flow fields and better understanding of the mechanisms in the formation of them. The consistency of the experimental data and numerical results are fairly good.The major conclusions drawn from this study are following:1. Flow characteristics of the impingement holes are comparatively simple. The impinging airflow was pushed downstream slightly by the effect of the cross-flow in the passage. The effect of the cross flow was not significant due to mass flow rate in the passage was relatively small.2. The interaction of the jets and with the cross-flow leads to the formation of the complicated flow pattern in the passage. Many vortices induced by the jets are observed. The vortices push the impinging flows moving upward and laterally. Theblockage effect of the jets forces the flow moving around the jets in the passage. High velocity flows not only exist on the target wall but also on the side and top walls of the passage.3. Flow pattern in the exit hole is mainly controlled by the flow pattern in the passage. Vortex is formed in the exit hole due to the non-uniform flow field at its inlet the strength of the vortex is increased with reducing passage height. Variation of the rotating direction dependent on height of the passage is measured. Vortex and large sized separation zones lead to highly non-uniform flow fields in the exit hole and very low values of discharge coefficients.4. Channel height/jet hole diameter ratio plays the most important role in the flow field characteristics but the variation of Reynolds number in the range of present investigation does not create obvious impact on the flow pattern.5. The experimental and numerical results show good consistency about the flow characteristics.