以平板邊界層流場探討不同幾何激紊器效果之SPIV實驗研究

EXPERIMENTAL STUDY FOR THE EFFECTS OF DIFFERENT GEOMETRIC TURBULENCE STIMULATORS ON BOUNDARY LAYER FLOW OVER A FLAT PLATE USING SPIV

船模實驗中，因尺度效應（scale effect）影響，需使用激紊器（turbulence stimulator）使船模表面邊界層（boundary layer）提早由層流（laminar flow）激發成紊流（turbulent flow），以促使模型與原型（實尺寸船舶）能儘量達成動力相似性（dynamic similarity）。然而，船模實驗採用之激紊器種類（幾何）、尺寸、黏貼位置等參數選擇，目前仍是實驗流體力學中的一大課題。
本研究於國立臺灣海洋大學系統工程暨造船學系的小型封閉式循環水洞中裝置一平板（flat plate）來產生邊界層流場，在入流速U0 = 0.25 m/s條件下，使用立體式質點影像測速法（stereoscopic particle image velocimetry，SPIV）進行三種不同幾何的激紊器：（1）三角形截面長細線、（2）圓形截面長細線、（3）螺樁線陣列之三維跡流場量測，並探討各自所激發出的紊流之特性。實驗結果顯示，三種激紊器皆能有效地使平板邊界層提早激發成紊流邊界層；按照激發出的紊流強度與範圍大小（激紊能力）排列的順序為：三角形截面長細線>圓形截面長細線>螺樁線陣列。

In model ship experiments, due to the scale effect, turbulence stimulators are used to induce an earlier transition of the boundary layer from laminar flow to turbulent flow on the model surface. This is to enhance the dynamic similarity between the model and the prototype (full-sized ship). However, the selection of parameters such as the type (geometry), size, and position of turbulence stimulators used in model ship experiments remains a major issue in experimental fluid dynamics.
This study installed a flat plate in the small closed-loop water tunnel at the Department of Systems Engineering and Naval Architecture, National Taiwan Ocean University, to generate a boundary layer flow field. Under the condition of inflow speed U0 = 0.25 m/s, three different geometries of turbulence stimulators were used: (1) long-thin line with a triangular cross-section, (2) long-thin line with a circular cross-section, and (3) row array of cylindrical studs. The three-dimensional wake flow fields were measured using Stereoscopic Particle Image Velocimetry (SPIV), and the characteristics of the turbulent flows induced by each were investigated. The experimental results showed that all three turbulence stimulators effectively caused the flat plate boundary layer to transition into a turbulent boundary layer earlier. The order of turbulence intensity and extent (turbulence enhancement capability) was as follows: long-thin line with a triangular cross-section > long-thin line with a circular cross-section > row array of cylindrical studs.