Long Channel Staggered Jet Impingement Flow Characteristics Of Study

Staggered arrangement impingement cooling has been used widely in turbine machine, with individual or connected cavities cast into the modern turbine blade wall, and employs an optimize combination of impingement cooling performance, suction effects and confined passages. The detailed knowledge of the heat transfer enhancement in this configuration is required for the optimization of the cooling design. This thesis describes the experimental and numerical researches of the flow characteristics inside the staggered arrangement impingement cooling system, and numerical analysis is compared and validated with the experimental results.Experiments were conducted with large-scaled models made of Plexiglas. Twelve staggered impingement holes and a larger outlet hole on the center line in one side of the confined channel was chosen to represent part of the typical impingement cooling system. The diameter of the outlet hole is 4 times of that of the impingement hole when the orifice-to-target-wall spacing altered as 1 3 and 5 times. While flow parameters— Re and spacing Z, change, the flow fields in the cooling passage and holes will vary accordingly. The influence of altering Re and Z_r to the flow characteristics, parameters and coefficient were detailed investigated.Parts of the experimental and numerical results were presented in the thesis, which are helpful to understand intrinsic mechanisms of the heat transfer enhancement in the confined channel with staggered jet arrangement. The experimental and numerical results show consistency about the flow structures, which testify the accuracy of the experiment and the credibility of the numerical method. The major conclusions of this study are following:1. In the upstream region of the channel, jets impinge on the target wall and are affected by neighboring jets. The cross-flow formed by upstream jets grows stronger increasingly in the channel along the main flow direction. In the downstream region, it attends to deflect the jets away from theirs impinging location and leads to the similarity of flow characteristics, when it is also forced to pass round the jet. The spacing-to-diameter ratio( Z_r) of the channel plays a dominant role to the flow characteristics in the channel, when the Reynolds number shows little influence.2. A strong counter clockwise vortex forms at the end of the channel and develops into the outlet hole at the smallest value of Z_r = 1, which is caused by staggered jets arrangement, obstacle of the end wall and reverse pressure gradient. It leads to serious flow separation and local reverse flow, and prevent full developmentof the flow in the outlet hole. The counter clockwise vortex is replace by two nearly symmetric corner vortices as the spacing ratio Z_r increased to 3 and 5. Separation region decreases and reverse flow vanishes in the outlet hole, and the flow distribution becomes more uniform and fully developed. The Reynolds number has little influence to the flow characteristics and no contribution to the flow development in outlet hole.3. In the impingement holes, flows were contracted at inlet and then expanded out. The staggered arrangement of jet holes and cross-flow in the channel have important influences on the flow of impingement holes outlet. In the condition of same spacing-to-diameter ratio, the jet velocities were increased and static pressures were decreased continuously along the channel, but the variations were reduced at high Z_r.4. Mass flow flux ratio, static pressure coefficients and discharge coefficients of impingement holes changed more rapidly in the downstream region of the channel as Z_r = 1. Mass flow flux ratio variation turn to be linear and has less effect on the changing of discharge coefficient. No obvious influence of Reynolds number was a little obvious at high Reynolds number on these parameters were observed, it became slightly larger at high Reynolds number.5. The numerical results reveal the details of the flow patterns and provide good knowledge of the jet impingements in confined passage. The consis...