本實驗以15*0.6*0.6m之循環渠道試驗急變明渠水流通過不同長度透水結構物研究其平均流速與其紊流特性。於渠道入口下游8.25m處放置以玻璃珠組成之高0.075m寬0.6m之透水塊體。預備試驗發現超過結構物6倍高時結構物上方出現類似透水底床之近似水平水面線，因此以0.15m（A組）、0.30m（B組）和0.45m（C組）作為本實驗的試驗長度，而結構物孔隙率為0.433。
結構物內部及外部流場分別以25Hz之音波vectrino流速儀及10Hz之電磁式流速儀量測，所有試驗之流量為0.0376 m3/s而入口雷諾數為62735.5。由積分計算結構物上方流速、結構物內部流量比例及水流強度削減程度。結構物內部流量變化為總量量之5-24%，在結構物前端及末端水流強度削減量介於16-24%。A、B、C三組實驗臨界水深FrD=1分別發生於l/L=0.499、0.473及0.384處，其水深皆小於無滲流之流況。
平均流速及紊流強度量測也於此論文中，然而由於挾氣現象會發生於此急變明渠流場中，特別是結構物後方，使得量測所得之數據及分佈圖無法確認其正確性，因此需要更進一步的確認。

The present experimental study is to investigate the mean velocity and turbulence characteristics of rapidly varied free surface flow through permeable structure of different lengths. Experiments are conducted in a 15*0.6*0.6m circulating flume in which permeable blocks made of glass beads at a height of 0.075m and width of 0.6m are mounded at 8.25m from flume entrance as the structure model. Preliminary test runs are conducted and indentify that water flow over a block of a length more than 6 block height would function as a porous bed. The lengths of the models thus are set at 0.15, 0.30 and 0.45m representing Cases A, B and C respectively. Geometric porosity of the model is 0.433.
The instantaneous velocity fields outside and inside of the block models are measured by using a side-looking ultrasonic wave vectrino velocimeter at 25Hz and an electromagnetic velocimeter at 10Hz, respectively. The inflow discharge and entrance Reynolds number for all tests are 0.0376 m3/s and 62735.5. By integration the velocities above the block, the flow rate inside the block, or the flow reduction, can be estimated. The reductions vary between 5-24% of the inflow discharge. Large reductions occur near block front and end sections at a value of around 16-24%. The critical depths are located at l/L=0.499, 0.473 and 0.384 for the cases A, B and C where the Froude number is 1. These critical depths are smaller than the value without the penetrating flow.
The mean flow and turbulence intensity distributions of the measurements are also presented in this thesis. However the air entrainment in this rapid varied flow field, particular at the rear of the block, limits the confidence of interpreting the ADV data. Some values and pattern of the distribution may be correct but still they need a further confirmation.

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