Abstract
In boundary layer flow around rotating machines, a radial (or cross-flow) velocity exists due to Coriolis and centrifugal forces. This velocity component can be of great importance for laminar-turbulent transition. A series of direct numerical simulations (DNS) are performed to study the boundary layer flow transition on a rotating Horizontal Axis Wind Turbine blade. To quantify the effect of blade rotation, results are compared with that from airfoil DNS, where the section is taken from 3D blades and does not rotate. It is shown that the rotation gives rise to a small radial velocity and slightly modifies the shape of unstable waves. However, the transition location and mechanism of 3D blade boundary layer flow resemble 2D flow for the investigated case.
Highlights
Horizontal Axis Wind Turbine (HAWT) blade consists of a series of 2D airfoil sections with different thicknesses, chord lengths, and twist angles
This paper aims to provide a such study to better understand the boundary layer laminar-turbulent transition on HAWT blade
In this paper, numerical simulations resolving the boundary layer laminar-turbulent transition are performed for the flow around a rotating LM38.8 blade
Summary
Horizontal Axis Wind Turbine (HAWT) blade consists of a series of 2D airfoil sections with different thicknesses, chord lengths, and twist angles. In the design and optimization of HAWT, Blade Element Theory (BET) is widely used. After dividing the blade into sections (or elements) in the spanwise direction, BET assumes that the flow around each section is locally 2-dimensional. As early as 1945, Himmelskamp [4] has observed that the lift coefficient for the rotating blade is increased compared with the non-rotating case, and the stall is postponed. This phenomenon is referred to as rotational augmentation in the later literature. It is well recognized that rotational augmentation is closely related to the large radial velocities in flow separation regions. The radial velocity induces a streamwise Coriolis force, which partially counteracts the adverse pressure gradient [6]
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