Enhancement of the leading-edge separation vortices by trailing-edge lateral blowing

AIAA Journal ◽  
1996 ◽  
Vol 34 (9) ◽  
pp. 1943-1945 ◽  
Author(s):  
Koji Miyaji ◽  
Kozo Fujii ◽  
Keiichi Karashima
Keyword(s):  
Leading Edge ◽  
Trailing Edge ◽  
Edge Separation

Three-Dimensional and Rotational Aerodynamics on the NREL Phase VI Wind Turbine Blade

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Alvaro Gonzalez ◽  
Xabier Munduate
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Three Dimensional ◽  
Separated Flow ◽  
Leading Edge ◽  
Wind Turbine Blade ◽  
Trailing Edge ◽  
Rotating Blade ◽  
Nrel Phase Vi ◽  
Edge Separation

This work undertakes an aerodynamic analysis over the parked and the rotating NREL Phase VI wind turbine blade. The experimental sequences from NASA Ames wind tunnel selected for this study respond to the parked blade and the rotating configuration, both for the upwind, two-bladed wind turbine operating at nonyawed conditions. The objective is to bring some light into the nature of the flow field and especially the type of stall behavior observed when 2D aerofoil steady measurements are compared to the parked blade and the latter to the rotating one. From averaged pressure coefficients together with their standard deviation values, trailing and leading edge separated flow regions have been found, with the limitations of the repeatability of the flow encountered on the blade. Results for the parked blade show the progressive delay from tip to root of the trailing edge separation process, with respect to the 2D profile, and also reveal a local region of leading edge separated flow or bubble at the inner, 30% and 47% of the blade. For the rotating blade, results at inboard 30% and 47% stations show a dramatic suppression of the trailing edge separation, and the development of a leading edge separation structure connected with the extra lift.

Effects of Initial Acceleration on the Flow Field Development Around Rapidly Pitching Airfoils

1995 ◽  
Vol 117 (1) ◽  
pp. 45-49 ◽  
Author(s):  
C. P. Gendrich ◽  
M. M. Koochesfahani ◽  
M. R. Visbal
Keyword(s):  
Leading Edge ◽  
Flow Front ◽  
Reversed Flow ◽  
Trailing Edge ◽  
Field Development ◽  
Surface Pressure Distribution ◽  
Constant Pitch ◽  
Acceleration Period ◽  
Initial Acceleration ◽  
Edge Separation

Computational results are presented to show how the acceleration period at the start of nominally constant pitch rate trajectories affects the dynamic stall process. Large amplitude motions of an NACA 0012 airfoil pitching about the quarter-chord axis were studied using constant (ON/OFF) acceleration profiles with nondimensional acceleration periods ranging between 0.039 to 0.6, and large pitch rates (0.1 ≤ Ω* ≡ α˙ c/2U∞≤0.4). The initial acceleration is observed to affect the integrated loads, surface pressure distribution, and the evolution of reversed flow regions just above the surface of the airfoil only during the acceleration period and for a relatively short time δτ ≤ 0.25 afterwards; τ≡ tU∞/c. After that time, all of these quantities only depend on the instantaneous angle of attack for a given pitch rate. These results are consistent with and explain previous experimental flow visualization observations. The onset of leading edge separation at high and low pitch rates is shown to be characterized by different processes. At low pitch rates leading edge separation occurs after the reversed flow front originating at the trailing edge has reached the leading edge. At higher pitch rates leading edge separation and the upstream progression of the (trailing edge) reversed flow front develop independently.

Calculation of Attached or Partially Separated Flow Around Airfoil Sections

1977 ◽  
Vol 21 (02) ◽  
pp. 69-81
Author(s):  
Jerome H. Milgram
Keyword(s):  
Separated Flow ◽  
Leading Edge ◽  
Perturbation Series ◽  
Unified Theory ◽  
Physical Plane ◽  
Trailing Edge ◽  
Separation Flows ◽  
Attached Flow ◽  
Approach Zero ◽  
Edge Separation

Two-dimensional airfoil theory is developed for incompressible flow, for which most aspects of the solution are found in a "mapped plane." Although the airfoil contour has large slopes in the physical plane when the airfoil has a round leading edge, the slopes in the mapped plane are small and uniformly approach zero as the airfoil thickness and camber ratios are made to approach zero by an affine transformation on the airfoil shape. Because of the small slopes in the mapped plane, a perturbation series is appropriate there. A relatively unified theory is given for attached and partially separated (trailing-edge separation) flows. The results of calculations by this theory are compared with the results of other theories and with measurements. The attached-flow theory is shown to be especially appropriate for thin marine propeller sections with blunted leading edges. Some new data on the pressure distribution across the wake at the trailing edge of an airfoil in partially separated flow are presented.

Rotational temperature imaging of a leading-edge separation in hypervelocity flow

2019 ◽  
Author(s):  
Laurent M. Le Page ◽  
Matthew Barrett ◽  
Sean O’Byrne ◽  
Sudhir L. Gai
Keyword(s):  
Rotational Temperature ◽  
Leading Edge ◽  
Temperature Imaging ◽  
Edge Separation

Effect of kinematics of orogenic wedge on kinematic evolutionary paths and deformation profiles of major shear zones: An example from the eastern Himalaya 

2021 ◽  
Author(s):  
Pritam Ghosh ◽  
Kathakali Bhattacharyya
Keyword(s):  
Shear Zone ◽  
Strain Softening ◽  
Leading Edge ◽  
Shear Zones ◽  
Deformation History ◽  
Progressive Deformation ◽  
Trailing Edge ◽  
Orogenic Wedge ◽  
Transport Direction ◽  
Evolutionary Paths

<p>We examine how the deformation profile and kinematic evolutionary paths of two major shear zones with prolonged deformation history and large translations differ with varying structural positions along its transport direction in an orogenic wedge. We conduct this analysis on multiple exposures of the internal thrusts from the Sikkim Himalayan fold thrust belt, the Pelling-Munsiari thrust (PT), the roof thrust of the Lesser Himalayan duplex (LHD), and the overlying Main Central thrust (MCT). These two thrusts are regionally folded due to growth of the LHD and are exposed at different structural positions. The hinterlandmost exposures of the MCT and PT zones lie in the trailing parts of the duplex, while the foreland-most exposures of the same studied shear zones lie in the leading part of the duplex, and thus have recorded a greater connectivity with the duplex. The thicknesses of the shear zones progressively decrease toward the leading edge indicating variation in deformation conditions. Thickness-displacement plot reveals strain-softening from all the five studied MCT and the PT mylonite zones. However, the strain-softening mechanisms varied along its transport direction with the hinterland exposures recording dominantly dislocation-creep, while dissolution-creep and reaction-softening are dominant in the forelandmost exposures. Based on overburden estimation, the loss of overburden on the MCT and the PT zones is more in the leading edge (~26km and ~15km, respectively) than in the trailing edge (~10km and ~17km, respectively), during progressive deformation. Based on recalibrated recrystallized quartz grain thermometer (Law, 2014), the estimated deformation temperatures in the trailing edge are higher (~450-650°C) than in the leading edge (350-550°C) of the shear zones. This variation in the deformation conditions is also reflected in the shallow-crustal deformation structures with higher fracture intensity and lower spacing in the leading edge exposures of the shear zones as compared to the trailing edge exposures.</p><p>The proportion of mylonitic domains and micaceous minerals within the exposed shear zones increase and grain-size of the constituent minerals decreases progressively along the transport direction. This is also consistent with progressive increase in mean R<sub>s</sub>-values toward leading edge exposures of the same shear zones. Additionally, the α-value (stretch ratio) gradually increases toward the foreland-most exposures along with increasing angular shear strain. Vorticity estimates from multiple incremental strain markers indicate that the MCT and PT zones generally record a decelerating strain path. Therefore, the results from this study are counterintuitive to the general observation of a direct relationship between higher Rs-value and higher pure-shear component. We explain this observation in the context of the larger kinematics of the orogen, where the leading edge exposures have passed through the duplex structure, recording the greatest connectivity and most complete deformation history, resulting in the weakest shear zone that is also reflected in the deformation profiles and strain attributes. This study demonstrates that the same shear zone records varying deformation profile, strain and kinematic evolutionary paths due to varying deformation conditions and varying connectivity to the underlying footwall structures during progressive deformation of an orogenic wedge.</p>

Wing Mechanics and Take-Off Preparation of Thrips (Thysanoptera)

1980 ◽  
Vol 85 (1) ◽  
pp. 129-136 ◽  
Author(s):  
C. P. ELLINGTON
Keyword(s):  
Leading Edge ◽  
Morphological Features ◽  
Inertial Forces ◽  
Wing Area ◽  
Trailing Edge ◽  
Lateral Projection ◽  
Parking Problem ◽  
Closed Position ◽  
Open Position ◽  
Fringe System

1. All of the wing fringe cilia of Thrips physapus, except those along the hindwing leading edge, pivot in elongated sockets which lock them into two positions. 2. The wings lie parallel over the abdomen when not in use, with the cilia locked in the closed position at an angle of 15-20° to the wing axis. The closing of the fringes prevents entanglement of the trailing edge cilia and lateral projection of the forewing leading edge cilia. 3. During flight the cilia are locked in the open position, doubling the wing area. The locking force is stronger than the combined aerodynamic and inertial forces on the cilia. 4. The fringes are opened by abdominal combing and closed by tibial combing. 5. The same morphological features are found in other members of the sub-order Terebrantia. Parallel wings at rest are characteristic of this suborder, and the collapsible fringe system is viewed as an effective method for parking the wings. 6. The fringes of the sub-order Tubulifera are not collapsible. The wings overlap on the abdomen at rest and a similar parking problem does not arise.

On the Breakdown at High Incidences of the Leading Edge Vortices on Delta Wings

1960 ◽  
Vol 64 (596) ◽  
pp. 491-493 ◽  
Author(s):  
B. J. Elle
Keyword(s):  
High Speed ◽  
Recent Article ◽  
Vortex Breakdown ◽  
Leading Edge ◽  
Critical Value ◽  
Delta Wings ◽  
Edge Separation ◽  
Leading Edge Vortices

In a recent article, H. Werlé, has described how the free spiral vortices on delta wings with leading edge separation suddenly expand if the incidence is increased beyond a critical value. His description conforms to a great extent with the results, arrived at during an English investigation of the same phenomenon (called the vortex breakdown), but the interpretations of the observations, suggested by the two sources, are different. Against this background it is felt that some further comments and some pertinent high speed observations, may be of interest.

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