scholarly journals Selection and impact of leading edge on boundary layer transition

2020 ◽  
Author(s):  
Dinesh Devraj Bhatia ◽  
Guangjun Yang ◽  
Guangning Li ◽  
Jian Wang
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Flow Structure ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Stagnation Region ◽  
Leading Edges ◽  
The Impact ◽  
Selection Of

Abstract The choice of leading edge aspect ratio (AR) plays a crucial role when planning boundary layer experimental wind tunnel tests on a flat plate. Poor selection of the leading-edge profile hampers the effectiveness of the experiment and increases testing costs associated with interchanging of leading edges to attain accurate results. Thus, the appropriate selection of the leading edge is a very crucial part of the wind tunnel experimental process. The authors, in this paper, argue that the curvature of the leading edge and thus the AR are of paramount importance to attain accurate results from wind tunnel testing. In this paper, the authors have tested 7 different elliptical leading edges and compared their performance with an ideal leading edge with zero thickness. Experimental and computational has been presented for leading edges ranging from AR6 to AR20. Results were evaluated for boundary layer transition onset location and it was found that AR20 has the least influence on the flow structure when compared the ideal leading edge. A study of the flow structure at the stagnation point indicates an increase in adverse pressure gradient with an increase in the AR but also a decrease in the size of the stagnation region. The presence of a higher AR leading edge reduces the turbulent spot production rate which is one of the primary causes of boundary layer transition. The authors have presented a correlation which makes it easier for aerodynamicists to quantify the impact of the leading-edge AR on transition. A case is also presented to compare the relative performance of a wedge and the higher AR leading edge which gives potential researchers the choice between an elliptical or a wedge-shaped leading edge.

Aerodynamics of leading-edge protection tapes for wind turbine blades

2020 ◽  
pp. 0309524X2097544
Author(s):  
Desirae Major ◽  
Jose Palacios ◽  
Mark Maughmer ◽  
Sven Schmitz
Keyword(s):  
Boundary Layer ◽  
Wind Turbine ◽  
Numerical Models ◽  
Turbine Blades ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Wind Turbine Blades ◽  
Layer Transition ◽  
Tape Edge ◽  
The Impact

This paper presents results of a comparative study on the effect of standard and tapered leading-edge protection (LEP) tapes on the annual energy production (AEP) of a utility-scale 1.5 MW wind turbine. Numerical models are developed in STAR-CCM+ to estimate the impact of LEP tapes on lift and drag coefficients of an NACA 64-618 airfoil operating at Re = 3 × 106. Experimental drag coefficient data are collected for LEP tapes applied to the tip-section of a de-commissioned wind turbine blade for numerical validation. The objective is to determine the physical mechanisms responsible for the aerodynamic degradation observed with standard LEP tapes, and to design a tapered LEP tape that reduces the associated adverse impact on AEP. An in-house wind turbine design and analysis code, XTurb-PSU, is used to estimate AEP using airfoil data obtained by STAR-CCM+. For standard LEP tapes, laminar-to-turbulent boundary-layer transition occurs at the LEP tape edge, resulting in AEP losses of 2%–3%. Comparable tapered LEP tapes can be designed to suppress boundary-layer transition for backward-facing step heights below a critical value such that associated impact on AEP is negligible.

Keel Design for Low Viscous Drag

1987 ◽  
Author(s):  
Clifford J. Obara ◽  
C. P. van Dam
Keyword(s):  
Boundary Layer ◽  
Laminar Flow ◽  
Laminar Boundary Layer ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Viscous Drag ◽  
Hydrodynamic Characteristics ◽  
Sweep Angle ◽  
Layer Transition ◽  
Layer Flow

In this paper, foil and planform parameters which govern the level of viscous drag produced by the keel of a sailing yacht are discussed. It is shown that the application of laminar boundary-Layer flow offers great potential for increased boat speed resulting from the reduction in viscous drag. Three foil shapes have been designed and it is shown that their hydro­dynamic characteristics are very much dependent on location and mode of boundary-Layer transition. The planform parameter which strongly affects the capabilities of the keel to achieve laminar flow is lea ding-edge sweep angle. The two significant phenomena related to keel sweep angle which can cause premature transition of the laminar boundary layer are crossflow instability and turbulent contamination of the leading-edge attachment line. These flow phenomena and methods to control them are discussed in detail. The remaining factors that affect the maintainability of laminar flow include surface roughness, surface waviness, and freestream turbulence. Recommended limits for these factors are given to insure achievability of laminar flow on the keel. In addition, the application of a simple trailing-edge flap to improve the hydrodynamic characteristics of a foil at moderate-to-high leeway angles is studied.

Effects of Weak Free Stream Nonuniformity on Boundary Layer Transition (Keynote Paper)

2003 ◽  
Author(s):  
Jonathan H. Watmuff
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Mean Flow ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Tollmien Schlichting ◽  
Distorted Waves ◽  
Thickness Variations

Experiments are described in which well-defined FSN (Free Stream Nonuniformity) distributions are introduced by placing fine wires upstream of the leading edge of a flat plate. Large amplitude spanwise thickness variations are present in the downstream boundary layer resulting from the interaction of the laminar wakes with the leading edge. Regions of elevated background unsteadiness appear on either side of the peak layer thickness, which share many of the characteristics of Klebanoff modes, observed at elevated Free Stream Turbulence (FST) levels. However, for the low background disturbance level of the free stream, the layer remains laminar to the end of the test section (Rx ≈ l.4×106) and there is no evidence of bursting or other phenomena associated with breakdown to turbulence. A vibrating ribbon apparatus is used to demonstrate that the deformation of the mean flow is responsible for substantial phase and amplitude distortion of Tollmien-Schlichting (TS) waves. Pseudo-flow visualization of hot-wire data shows that the breakdown of the distorted waves is more complex and occurs at a lower Reynolds number than the breakdown of the K-type secondary instability observed when the FSN is not present.

Criteria for Boundary Layer Transition

2011 ◽  
Author(s):  
Stefan Becker ◽  
Donald M. McEligot ◽  
Edmond Walsh ◽  
Eckart Laurien
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Boundary Layer Flow ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Turbulence Level ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Layer Transition ◽  
Layer Flow

New results are deduced to assess the validity of proposed transition indicators when applied to situations other than boundary layers on smooth surfaces. The geometry employed utilizes a two-dimensional square rib to disrupt the boundary layer flow. The objective is to determine whether some available criteria are consistent with the present measurements of laminar recovery and transition for the flow downstream of this rib. For the present data — the proposed values of thresholds for transition in existing literature that are based on the freestream turbulence level at the leading edge are not reached in the recovering laminar run but they are not exceeded in the transitioning run either. Of the pointwise proposals examined, values of the suggested quantity were consistent for three of the criteria; that is, they were less than the threshold in laminar recovery and greater than it in the transitioning case.

Boundary-Layer Transition Detection in a Cryogenic Wind Tunnel Using Luminescent Paint

1997 ◽  
Vol 34 (1) ◽  
pp. 34-42 ◽  
Author(s):  
Keisuke Asai ◽  
Hiroshi Kanda ◽  
Tetsuya Kunimasu ◽  
Tianshu Liu ◽  
John P. Sullivan
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Cryogenic Wind Tunnel
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