Abstract
The transition in the boundary layer is investigated using infrared thermography (IRT). The study is carried out on a laminar airfoil in the transonic intermittent in-draft wind tunnel. The transition in the boundary layer is evocated using transition-generator strips of different thicknesses at two Mach numbers: 0.4 and 0.8. The tested transition-generators thickness to boundary layer displacement thickness ratio was from 0.42 to 1.25. The Reynolds number respect to the airfoil chord is: Re = 1.0 – 1.4·106. The six cases for different transition-generators thickness ratios were compared. The behaviours of laminar and turbulent boundary layers are discussed. The use of IRT has been proven to be an appropriate tool for detecting the transition of the boundary layer in high-speed wind tunnel testing.
Highlights
To study the development of the boundary layer and the transition from the laminar to the turbulent flow in the boundary layer is very important because it fundamentally changes the character of the boundary layer; it means the parameters of the boundary layer and its behaviour
To gain a better idea of how to use the transitiongenerator strips and how they can affect the transition in the boundary layer, an experiment was performed on the laminar airfoil in the transonic testing section at two Mach numbers and three different strips thickness
Initially stable laminar boundary layer, unstable (Tollmien-Schlichting) waves gradually begin to occur after reaching the Rekr, which gradually passes into three-dimensional vortices
Summary
To study the development of the boundary layer and the transition from the laminar to the turbulent flow in the boundary layer is very important because it fundamentally changes the character of the boundary layer; it means the parameters of the boundary layer and its behaviour. How the boundary layer behaves especially in critical flow regimes depends mainly on its nature and how the boundary layer is developed.This is important both in aerospace applications where the airplane's lift depends on the separation of the boundary layer from the wing airfoil and in the applications in the drive units and other turbomachinery applications of various power aggregates where the performance and efficiency of these machines depends on the nature of the boundary layer and its possible separation For these reasons, it is necessary to address the boundary layer's nature, to examine under what conditions and how soon the transition of the laminar boundary layer into turbulence occurs. The strips with roughness elements are used at varying distances at the leading edge of testing airfoil or wings when there is a need to fix the boundary layer transition This can be the case of prismatic blades testing when inlet flow conditions (low inlet turbulence intensity along with a low Reynolds number) can cause the boundary layer to remain laminar up to the blades trailing edge. To gain a better idea of how to use the transitiongenerator strips and how they can affect the transition in the boundary layer, an experiment was performed on the laminar airfoil in the transonic testing section at two Mach numbers and three different strips thickness
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