Boundary Layer State and Flow Field Structure Underlying Rotational Augmentation of Blade Aerodynamic Response

2003 ◽  
Vol 125 (4) ◽  
pp. 448-456 ◽  
Author(s):  
S. Schreck ◽  
M. Robinson
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Normal Force ◽  
Unsteady Aerodynamics ◽  
Boundary Layer Separation ◽  
Pressure Data ◽  
Horizontal Axis Wind Turbine ◽  
Pressure Distributions ◽  
Standard Deviations ◽  
Tunnel Time

Blade rotation routinely and significantly augments aerodynamic forces during zero yaw horizontal axis wind turbine (HAWT) operation. To better understand the flow physics underlying this phenomenon, time dependent blade surface pressure data were acquired from the National Renewable Energy Laboratory (NREL). Unsteady Aerodynamics Experiment (UAE), a full-scale HAWT tested in the NASA Ames 80-by-120-foot wind tunnel. Time records of surface pressures and normal force were processed to obtain means and standard deviations. Surface pressure means and standard deviations were analyzed to identify boundary layer separation and shear layer impingement locations. Separation and impingement kinematics were then correlated with normal force behavior. Results showed that rotational augmentation was linked to specific separation and impingement behaviors, and to associated three-dimensionality in surface pressure distributions.

Structures and Interactions Underlying Rotational Augmentation of Blade Aerodynamic Response

2003 ◽  
Author(s):  
S. Schreck ◽  
M. Robinson
Keyword(s):  
Surface Pressure ◽  
Normal Force ◽  
Unsteady Aerodynamics ◽  
Boundary Layer Separation ◽  
Time Dependent ◽  
Blade Surface ◽  
Pressure Data ◽  
Pressure Distributions ◽  
Standard Deviations ◽  
Tunnel Time

Blade rotation routinely and significantly augments aerodynamic forces during zero yaw HAWT operation. To better understand the flow physics underlying this phenomenon, time dependent blade surface pressure data were acquired from the NREL Unsteady Aerodynamics Experiment, a full-scale HAWT tested in the NASA Ames 80 ft × 120 Ft wind tunnel. Time records of surface pressures and normal force were processed to obtain means and standard deviations. Surface pressure means and standard deviations were analyzed to identify boundary layer separation and reattachment locations. Separation and reattachment kinematics were then correlated with normal force behavior. Results showed that rotational augmentation was linked to specific separation and reattachment behaviors, and to associated three-dimensionality in surface pressure distributions.

Rotational Augmentation of Horizontal Axis Wind Turbine Blade Aerodynamic Response

2002 ◽  
Author(s):  
S. Schreck ◽  
M. Robinson
Keyword(s):  
Wind Turbine ◽  
Surface Pressure ◽  
Unsteady Aerodynamics ◽  
Horizontal Axis ◽  
Pressure Data ◽  
Aerodynamic Forces ◽  
Horizontal Axis Wind Turbine ◽  
Pressure Distributions ◽  
Rotating Blade ◽  
Wind Tunnel Data

Surface pressure data were acquired using the NREL Unsteady Aerodynamics Experiment, a full-scale horizontal axis wind turbine, which was erected in the NASA Ames 80 ft × 120 ft wind tunnel. Data were collected first for a stationary blade, and then for a rotating blade with the turbine disk at zero yaw. Analyses compared aerodynamic forces and surface pressure distributions under rotating conditions against analogous baseline data acquired from the stationary blade. This comparison allowed rotational modifications to blade aerodynamics to be characterized in detail. Rotating conditions were seen to dramatically amplify aerodynamic forces, and radically alter surface pressure distributions. These and subsequent findings will more fully reveal the structures and interactions responsible for these flow field enhancements, and help establish the basis for formalizing comprehension in physics based models.

Surface Pressure Distribution on a Blade of a 10 m Diameter HAWT (Field Measurements versus Wind Tunnel Measurements)

2005 ◽  
Vol 127 (2) ◽  
pp. 185-191 ◽  
Author(s):  
T. Maeda ◽  
E. Ismaili ◽  
H. Kawabuchi ◽  
Y. Kamada
Keyword(s):  
Wind Tunnel ◽  
Surface Pressure ◽  
Field Measurements ◽  
Reynolds Numbers ◽  
Blade Surface ◽  
Pressure Data ◽  
Surface Pressure Distribution ◽  
Pressure Distributions ◽  
Wind Tunnel Data ◽  
Local Angle

This paper exploits blade surface pressure data acquired by testing a three-bladed upwind turbine operating in the field. Data were collected for a rotor blade at spanwise 0.7R with the rotor disc at zero yaw. Then, for the same blade, surface pressure data were acquired by testing in a wind tunnel. Analyses compared aerodynamic forces and surface pressure distributions under field conditions against analogous baseline data acquired from the wind tunnel data. The results show that aerodynamic performance of the section 70%, for local angle of attack below static stall, is similar for free stream and wind tunnel conditions and resemblances those commonly observed on two-dimensional aerofoils near stall. For post-stall flow, it is presumed that the exhibited differences are attributes of the differences on the Reynolds numbers at which the experiments were conducted.

Analytical Solutions for a Family of Gaussian Impinging Jets

2008 ◽  
Vol 75 (2) ◽  
Author(s):  
Zhuyun Xu ◽  
Horia Hangan ◽  
Pei Yu
Keyword(s):  
Boundary Layer ◽  
Excellent Agreement ◽  
Surface Pressure ◽  
Analytical Solutions ◽  
Reynolds Numbers ◽  
Impinging Jets ◽  
Experimental Results ◽  
Jet Flows ◽  
Pressure Distributions ◽  
Circular Plane

Various types of impinging jet flows are analytically modeled using inviscid free Gaussian jet solutions superimposed with experimentally fitted boundary layer models. Improved (more robust) and simplified solutions to existing models are defined. Velocity profiles, surface pressure distributions, and streamline plots are calculated for circular, plane, and annular impinging jets. The models show excellent agreement with existing experimental results in both laminar and turbulent conditions and for different Reynolds numbers.

Development of Blade Profiles for Low Pressure Turbine Applications

1996 ◽  
Author(s):  
E. M. Curtis ◽  
H. P. Hodson ◽  
M. R. Banieghbal ◽  
J. D. Denton ◽  
R. J. Howell ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Low Pressure ◽  
Blade Profile ◽  
Suction Surface ◽  
Number Range ◽  
Low Pressure Turbine ◽  
Pressure Distributions ◽  
Wide Range ◽  
Highly Loaded

This paper describes a programme of work, largely experimental, which was undertaken with the objective of developing an improved blade profile for the low-pressure turbine in aero-engine applications. Preliminary experiments were conducted using a novel technique. An existing cascade of datum blades was modified to enable the pressure distribution on the suction surface of one of the blades to be altered. Various means, such as shaped inserts, an adjustable flap at the trailing edge, and changing stagger were employed to change the geometry of the passage. These experiments provided boundary layer and lift data for a wide range of suction surface pressure distributions. The data was then used as a guide for the development of new blade profiles. The new blade profiles were then investigated in a low-speed cascade that included a set of moving bars upstream of the cascade of blades 10 simulate the effect of the incoming wakes from the previous blade row in a multistage turbine environment. Results are presented for two improved profiles that are compared with a datum representative of current practice. The experimental results include loss measurements by wake traverse, surface pressure distributions, and boundary layer measurements. The cascades were operated over a Reynolds Number range from 0.7 × 105 to 4.0 × 105. The first profile is a “laminar flow” design that was intended to improve the efficiency at the same loading as the datum. The other is a more highly loaded blade profile intended to permit a reduction in blade numbers. The more highly loaded profile is the most promising candidate for inclusion in future designs. It enables blade numbers to be reduced by 20%, without incurring any efficiency penalty. The results also indicate that unsteady effects must be taken into consideration when selecting a blade profile for the low-pressure turbine.

scholarly journals Effect of Air-Ducted Blade Design on Horizontal Axis Wind Turbine Performance

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3618
Author(s):  
Cemil Yigit
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Boundary Layer Separation ◽  
Optimization Method ◽  
Power Coefficient ◽  
Critical Number ◽  
Horizontal Axis Wind Turbine ◽  
Local Boundary ◽  
Response Surface Optimization ◽  
Computational Fluid Dynamics Analysis

Wind turbines without pitch control are more preferable from economical point of view but aerodynamic stall affects them more and after a critical wind speed local boundary layer separation occurs. Consequently, their power production is relatively low. In this study, air ducts added on the blade and using the airflow from them the kinetic energy of the low-momentum fluid behind the surface was increased and delay of separation of the boundary layer from the surface was examined The Response Surface Optimization method was utilized in order to get the best possible design under the constraints and targets arranged for the parameters termed the diameter, slope, number and angle of attack of the air ducts. By using computational fluid dynamics analysis, optimum parameter values were obtained and air-ducted and air-duct free blade designs were compared. An improvement in power coefficient between 3.4–4.4% depending on wind speed was achieved with the new design. Due to increase in viscous forces, more power from the rotor obtained by opening air ducts up to a critical number. However, the results showed that after the critical number of air duct addition of more duct on the blade reduced the power coefficient.

Streamwise Fluidelastic Instability in a Deformed Rotated Triangular Tube Array With Pitch-to-Diameter Ratio of 1.375

2015 ◽  
Author(s):  
Daniel B. Keogh ◽  
Craig Meskell
Keyword(s):  
Surface Pressure ◽  
Diameter Ratio ◽  
Streamwise Direction ◽  
Pressure Data ◽  
Steam Generators ◽  
Drag Forces ◽  
Surface Pressure Distribution ◽  
Pressure Distributions ◽  
Fluidelastic Instability ◽  
Stable Flow

A study of the surface pressure distribution of a cylinder in a deformed rotated triangular tube array with pitch-to-diameter ratio of 1.375 has been performed. This work was motivated by the failure of steam generators in San Onofre Nuclear Generating Station (SONGS) in Southern California, which occurred as a result of fluidelastic instability in the streamwise direction. This particular failure occurred in the U-bend region of the steam generators. The presence of anti-vibration bars (AVB) in this region prevent the tubes from experiencing fluidelastic insatiably (FEI) in the transverse direction but offer little support in the streamwise direction. This study analyses the streamwise direction vibration of the tubes in the U-bend region using experimental data and a simplified quasi-steady model. Surface pressure data was gathered in a draw down wind tunnel for a range of flow velocities using an instrumented cylinder with 36 pressure taps around the circumference of the cylinder at midplane. The instrumented cylinder was mounted in the 4th and 6th rows of the tube array. The effect of streamwise displacement of up to ±10% of the instrumented tube and its neighbours was investigated. Although bi-stable flow was detected, only the forces in the lift direction were substantially affected. The displacement dependent drag forces acting on the instrumented cylinder were determined by integrating the pressure distributions with respect to angle. Hence the coupled fluid stiffness matrix could be assembled for each flow velocity studied. The effect of Reynolds number was also investigated for a number of scenarios.

scholarly journals The Effect of Vortex Generators on Shock-Induced Boundary Layer Separation in a Transonic Convex-Corner Flow

Aerospace ◽  
2021 ◽  
Vol 8 (6) ◽  
pp. 157
Author(s):  
Kung-Ming Chung ◽  
Kao-Chun Su ◽  
Keh-Chin Chang
Keyword(s):  
Boundary Layer ◽  
Surface Pressure ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Streamwise Vorticity ◽  
Layer Separation ◽  
Convex Corner ◽  
Corner Flow ◽  
The Mean ◽  
Control Surfaces

Deflected control surfaces can be used as variable camber control in different flight conditions, and a convex corner resembles a simplified configuration for the upper surface. This experimental study determines the presence of passive vortex generators, VGs (counter-rotating vane type), on shock-induced boundary layer separation for transonic convex-corner flow. The mean surface pressure distributions in the presence of VGs for h/δ = 0.2 and 0.5 are similar to those for no flow control. If h/δ = 1.0 and 1.5, there is an increase in the amplitude of the mean surface pressure upstream of the corner’s apex, which corresponds to greater device drag and less downstream expansion. There is a decrease in peak pressure fluctuations as the value of h/δ increases, because there is a decrease in separation length and the frequency of shock oscillation. The effectiveness of VGs also depends on the freestream Mach number. For M = 0.89, there is an extension in the low-pressure region downstream of a convex corner, because there is greater convection and induced streamwise vorticity. VGs with h/δ ≤ 0.5 are preferred if deflected control surfaces are used to produce lift.

Sub boundary-layer vortex generators for the control of shock induced separation

2006 ◽  
Vol 110 (1106) ◽  
pp. 215-226 ◽  
Author(s):  
G. S. Cohen ◽  
F. Motallebi
Keyword(s):  
Boundary Layer ◽  
Total Pressure ◽  
Static Pressure ◽  
Pressure Rise ◽  
Boundary Layer Separation ◽  
Vortex Generators ◽  
Pressure Recovery ◽  
Flow Visualisation ◽  
Pressure Distributions ◽  
Pressure Profiles

Abstract The results of an investigation into the effects that sub-boundary layer vortex generators (SBVGs) have on reducing normal shock-induced turbulent boundary-layer separation are presented. The freestream Mach number and Reynolds number were M = 1·45 and 15·9 × 106/m, respectively. Total pressure profiles, static pressure distributions, surface total pressure distributions, oil flow visualisation and Schlieren photographs were used in the results analysis. The effects of SBVG height, lateral spacing and location upstream of the shock were investigated. A novel curved shape SBVG was also evaluated and comparisons against the conventional flat vane type were made. The results show that in all but two cases, separation was completely eliminated. As expected, the largest SBVGs with height, h = 55%δ, provided the greatest pressure recovery and maximum mixing. However, the shock pressure rise was highest for this case. The experiments showed that the mid height SBVG array with the largest spacing provided similar results to the SBVG array with the largest height. Reducing the distance to shock to 10δ upstream also showed some improvement over the SBVG position of 18δ upstream. It was suggested that total elimination of the separated region may not be required to achieve a balance of improved static pressure recovery whilst minimising the pressure rise through the shock. The effect of curving the SBVGs provided an improved near wall mixing with an improved static and surface total pressure recovery downstream of the separation line. The optimum SBVG for the current flow conditions was found to be the curved vanes of h = 40%δ, with the largest spacing, located at 18δ upstream of the shock. Overall, it was apparent from the results that in comparison to larger vortex generators with a height comparable to δ, for SBVGs the parameters involved become more important in order to obtain the highest degree of mixing from a given SBVG configuration.

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