臺灣博碩士論文加值系統

壁噴流在航空工業中已有廣泛的應用, 如薄膜冷卻,邊界層控制, 環流機
翼等. 當壁面出現曲度時會對噴流流場造成何種影響? 即是本文研究的重
點.本文針對平面噴流流經圓柱表面的流場, 做了流場觀察並量測其平均
速度分佈及頻譜圖, 並藉由改變出口速度, 出口高度及曲率半徑, 由其中
探討曲率半徑與出口雷諾數對噴流發展的影響.從流場觀察中發現, 在過
渡區內凸曲面效應對於壁上的誘生渦流具有壓抑作用, 造成曲面壁噴流的
發展反而比平板壁噴流慢. 在平均速度場的量測上, 則從最大速度遞減,
寬度成長及捲入量等特性, 證實了凸曲面壁的壓抑效應.在紊流完全發展
後, 則曲面壁噴流的發展就比平板快但其平均速度剖面則不受曲率半徑影
響, 其最大速度遞減及寬度成長可用 Um/Uo = Au*exp(Bu*(X/H)) Y.5/H
= Aw*exp(Bw*(X/H))之指數函數形態表示, 且 H/R 越大, 速度遞減越
快, 寬度成長也愈快, 與 Reh, Rer 無關.文中以 21 種不同狀況下之流
場, 統計出 Au, Bu,Aw, Bw 隨 H/R 之分佈, 併代入上述之指數函數中,
藉此預測最大速度之遞減與寬度成長,得到不錯之結果.

The flow field characteristics of a plane jet passing directly
over a circular cylinder, so-called curved wall jet, is studied
by flow visualization and measurements of the mean velocity
pro- file and energy spectra. The parameters investigated
include the jet exit high, H, jet exit velocity Uo, and the
cylinder diameter R. In flow visualization study, the induced
vortices near the wall are found to be supressed due to the
curvature effect in the transition region, and this phenomenum
delays the wall jet deve- lopment downstream. It is further
comfirmed by measuring the maximum velocity decay, the jet
width, and the entrainment flow rate. After the flow has
developed to be fully turbulent in the similarity region, the
curved wall jet grows faster than the plane wall jet. During
the evolving process, the growth of the jet width, Y.5, and the
decay of the maximum velocity, Um, can be expressed by an
expotential form: Um/Uo = Au*exp(Bu*(X/H)) Y.5/H = Aw*exp(Bw*(X/
H)) As H/R becomes large, the maximum velocity decays faster
and the width grows more rapidly. The values of Au, Bu, Aw, Bw
can be determined from the measurements. They are also found to
be func- tions of H/R. By substituting these parameters into
the equations above, the decay of Um and growth of Y.5 can be
predicted easily.