壓電材料聲波激擾法控制分離流研究

The Study of Flow Separation Control by Piezoelectric Material

蕭飛賓(Fei-Bin Hsiao) ； 胡育豪(Yu-Hau Hu) ； 潘大知(Dar-Tzi Pan)

《中華民國振動與噪音工程學會論文集》 1995 (1995/06) Pp. 189-202

https://doi.org/10.30028/CSSVANNUAL.199506.0189

摘要

近年來，利用聲波激擾法控制流場的分離，在流體力學與空氣動力學上，已經有許多成功且具體的成果，但聲波激擾之機構，不利於實際上的應用，而壓電材料(piezoelectric material)，能以交流電壓造成振動，機構較為簡單，廣泛應用於結構與振動的控制。但目前使用壓電材料作為流場控制的例子還很少。因此，本研究嘗試以PVDF（高分子壓電材料），直接黏貼於模型的表面，激擾分離的流場以探討壓電材料控制分離流場的效果。實驗是將平板模型與圓柱模型上黏貼PVDF，分別在兩個不同的開放吸入式風洞內進行流場的量測。平板模型的量測包括速度的量測與頻譜分析，實驗控制的變因是攻角、雷諾數與激發頻率。而圓柱模型的量測包括頻譜分析與圓柱表面壓力分佈，實驗控制變因為PVDF之激擾角度，激擾頻率與流場雷諾數。實驗結果發現平板流場經PVDF以風洞內部共振頻率激擾而圓柱流場經PVDF以剪層流不穩定頻率激擾後，流場頻譜有顯著的變化，證明了PVDF的振動可有效加強被激擾流場局部渦流結構。由PVDF的新激擾機構實驗可證實文獻中所提到外部聲波激擾法與內部聲波激擾法的觀點為正確，亦即當激擾頻率為風洞內部之共振頻率或剪層流不穩定頻率激擾分離流場時，可得最好的效果。

關鍵字

流場分離 ； 聲波激擾 ； 壓電材料 ； PVDF

並列摘要

This paper studies the control effectiveness of using piezoelectric material as a vibrating actuator to excite separated flow over objects. The polyvinylidene fluoride (PVDF) used here is a kind of polymer piezoelectric material which can exert transverse vibration with amplitude and frequency according to the external AC power supply. The 130m PVDF in thickness is striped to have a dimension of 20 cm by 1 cm and 12.5 cm by 0.3 cm, respectively, in order to be bonded on a flat-plate at the leading-edge, and on a circular cylinder. The parameters investigated for the flat-plate experiment include the Reynolds number, the angle of attack, and the excitation frequency, while for the cylinder experiment, the parameters include the Reynolds number, the excitation location, and excitation frequency. Both experiments are separately conducted in two subsonic wind tunnels. Energy spectra of the fluctuating velocities around the separated region are measured before and after PVDF's excitation. The associated surface pressure distribution is also measured in cylinder experiment. Results indicate that the periodic perturbations from PVDF have ability to enhance vertical flow structures when the excitation frequency of PVDF is close to either the wind tunnel resonance frequency or the shear layer instability frequency of the separated flow. Data also show that excitation has strongest effectiveness when the PVDF is located around the separation point of the cylinder model, which confirms previous results by using acoustics as an excitation tool.