Turbulence Intensity Effects on a Leading-Edge Separation Bubble of Flat Plate Wing at Low-Reynolds Numbers

Katsuya Kajiwara,Masayuki Anyoji

doi:10.4236/jfcmv.2020.84012

Abstract

In this study, we experimentally investigate the effects of mainstream turbulence intensity (Ti) on a leading-edge separation bubble under low-Reynolds number (Rec) conditions range of 2.0 × 104 to 6.0 × 104. We used a flat plate to fix a separation point at the leading edge. Also, we visualized the behavior of the leading-edge separation bubble using the smoke wire technique and Particle Image Velocimetry (PIV) measurement. Furthermore, we measured the effect of Ti on the turbulent transition process in the separated shear layer using a hot-wire anemometer. The results indicate that the bypass transition for large Ti causes the turbulent transition, and so accelerates the reattachment of the separated shear layer. The results show that the bypass transition promotes the reattachment of the separated shear layer to maintain the leading-edge separation bubble on the upper surface even at high angles of attack, increasing the stall angle.

Highlights

As aircraft become smaller and lighter, Micro Air Vehicles (MAVs) and Nano Air Vehicles (NAVs) for collecting information at disaster sites where no one can enter and conducting terrain surveys on complex terrain were being studied [1] [2]
As a general and distinguishing flow field [21] [22], at α = 0 ̊ and 2 ̊ in turbulence intensity (Ti) = 0.20%, the 2D and stable separated shear layer gradually becomes unstable in the downstream direction, and eventually, the 2D coherent vortex is formed by rolling up the separated shear layer
We evaluated the effects of the mainstream turbulence intensity (Ti) on the turbulence transition of the separated shear layer and the aerodynamic characteristics of the flat plate at low Rec range of Rec = 20,000 to 60,000

Summary

Introduction

As aircraft become smaller and lighter, Micro Air Vehicles (MAVs) and Nano Air Vehicles (NAVs) for collecting information at disaster sites where no one can enter and conducting terrain surveys on complex terrain were being studied [1] [2]. Since these aircraft have small wing areas and relatively low flight speed of about several tens of meters per second, they have low flight Reynolds number less than 100,000, based on the chord length. High-performance low-Reynolds number airfoils at around the cruising Reynolds number of 20,000 have been studied [5] [6]

Methods

Results

Conclusion