本研究利用紊流產生器及不同直管道長度置於背階管道入口，實驗探討不同背階入口條件在三維分離及再接觸流之流場特性。實驗使用小型風洞系統產生一均勻流，並將煙霧導入測試段管道。測試段管道使用透明壓克力製成，其背階高度為1.75 cm，展弦比為4，擴張比為1.33。將透明壓克力圓柱等距排列於測試段管道入口，形成6柱紊流產生器。與無紊流產生器的情況下搭配不同直管道長度探討不同背階入口條件對流場的影響。選取雷諾數約400至18000，包含層流至紊流數種流速，使用都卜勒雷射測速儀進行背階入口流場、再接觸長度(迴流區大小)、再接觸長度橫向分佈、三維分離及再接觸流不同斷面流場結構及上壁面迴流區等量測。 研究顯示，背階管道內再接觸長度變化，層流時隨雷諾數增加而增加，過渡流時隨雷諾數增加而減少，而紊流時不隨雷諾數增減。其中直管道長度增加後，會使得層流及過渡流之再接觸長度變長，紊流則是略為減少。並會提高過渡流及紊流起始雷諾數，使得過渡流及紊流延後發生。且增加了層流及過渡流的雷諾數範圍。而加裝紊流產生器後產生紊流強度時，再接觸長度變短；無紊流強度時，則反之。有紊流強度時會降低過渡流及紊流起始雷諾數，使得過渡流與紊流提早發生。並縮小了層流及過渡流的雷諾數範圍，尤其在過渡流時縮小迴流區範圍可達到50%。 The research experimentally investigates the effects of different backward-facing step inlet condition on the flow characteristics in three-dimensional separated and reattached flows. A wind tunnel system is used to generate a uniform flow into the inlet of the test section duct with smoke. Test section duct is made by transparent acrylics and the step height of the backward-facing step duct is 1.75 cm, aspect ratio is 4, and expansion ratio is 1.33. Investigate six-cylinder turbulator made by six transparent and cylindrical acrylics placed inside the duct with the same distance and no turbulator at the inlet of the test section duct with different duct length condition to generate the effect of the flows. The Reynolds number are between 500 and 17000, which cover the laminar, transitional and turbulent flows. The velocity measurements were conducted using laser Doppler velocimetry include the profile of the backward-facing step inlet, the reattachment length (the size of the recirculation region), the spanwise distribution of the reattachment length, the different flow structures of the three-dimensional separated and reattached, and the recirculation region of the flat wall. Results of this study show that the reattachment length increases with Reynolds number in the laminar flow region, decreases with Reynolds number in the transitional flow region, and almost remains constant with Reynolds number in the turbulent flow region. The reattachment length increases in the laminar and transitional flow region and decreases in the turbulent flow region when duct length increases. The transitional and turbulent flow are also delayed to generate, and the Reynolds number region of the laminar and transitional flow are also increased when duct length increases. The turbulator much reduces the reattachment length, and makes the transitional and turbulent flow to be generated early. The turbulator also can make the Reynolds number region of the laminar and transitional flow to be decrease, and the Reynolds number region of the transitional flow even can decrease to 50%.