Periodic Flow in a Wind Tunnel Produced by Rotating Shutters

1976 ◽  
Vol 98 (2) ◽  
pp. 278-281 ◽  
Author(s):  
G. Charnay ◽  
J. Mathieu
Keyword(s):  
Wind Tunnel ◽  
Resonance Frequency ◽  
Test Section ◽  
Wind Tunnel Test ◽  
Periodic Flow ◽  
Turbulence Level ◽  
Mean Velocity ◽  
The Mean ◽  
Velocity Skewness

The periodic flow obtained in a wind tunnel test section by means of an upstream pulsator is investigated. The turbulence level in this section is quite small and the direction of the periodic velocity is that of the mean velocity. The measurement of the velocity skewness and flatness factors indicates that true sinusoidal pulsation is achieved only for the resonance frequency which depends little on the length of the test section.

A wind tunnel simulation of the mean velocity fields behind upright porous fences

2007 ◽  
Vol 146 (1-2) ◽  
pp. 82-93 ◽  
Author(s):  
Zhibao Dong ◽  
Wanyin Luo ◽  
Guangqiang Qian ◽  
Hongtao Wang
Keyword(s):  
Wind Tunnel ◽  
Velocity Fields ◽  
Mean Velocity ◽  
Wind Tunnel Simulation ◽  
The Mean

scholarly journals Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different atmospheric inflow conditions

2016 ◽  
Author(s):  
Jan Bartl ◽  
Lars Sætran
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Turbulence Intensity ◽  
Wake Flow ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Blind Test ◽  
The Mean ◽  
Inlet Conditions ◽  
Inflow Conditions

Abstract. This is a summary of the results of the fourth Blind test workshop which was held in Trondheim in October 2015. Herein, computational predictions on the performance of two in-line model wind turbines as well as the mean and turbulent wake flow are compared to experimental data measured at NTNU's wind tunnel. A detailed description of the model geometry, the wind tunnel boundary conditions and the test case specifications was published before the workshop. Expert groups within Computational Fluid Dynamics (CFD) were invited to submit predictions on wind turbine performance and wake flow without knowing the experimental results at the outset. The focus of this blind test comparison is to examine the model turbines' performance and wake development up until 9 rotor diameters downstream at three different atmospheric inflow conditions. Besides a spatially uniform inflow field of very low turbulence intensity (TI = 0.23 %) as well as high turbulence intensity (TI = 10.0 %), the turbines are exposed to a grid-generated atmospheric shear flow (TI = 10.1 %). Five different research groups contributed with their predictions using a variety of simulation models, ranging from fully resolved Reynolds Averaged Navier Stokes (RANS) models to Large Eddy Simulations (LES). For the three inlet conditions the power and the thrust force of the upstream turbine is predicted fairly well by most models, while the predictions of the downstream turbine's performance show a significantly higher scatter. Comparing the mean velocity profiles in the wake, most models approximate the mean velocity deficit level sufficiently well. However, larger variations between the models for higher downstream positions are observed. The prediction of the turbulence kinetic energy in the wake is observed to be very challenging. Both the LES model and the IDDES (Improved Delayed Detached Eddy Simulation) model, however, are consistently managing to provide fairly accurate predictions of the wake turbulence.

A new low-turbulence wind tunnel for bird flight experiments at Lund University, Sweden

1997 ◽  
Vol 200 (10) ◽  
pp. 1441-1449 ◽  
Author(s):  
C J Pennycuick ◽  
T Alerstam ◽  
A Hedenström
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Test Section ◽  
Safety Net ◽  
Turbulence Level ◽  
Bird Flight ◽  
Contraction Ratio ◽  
Unrestricted Access ◽  
Side Walls ◽  
Air Speed

A new wind tunnel for experiments on bird flight was completed at Lund University, Sweden, in September 1994. It is a closed-circuit design, with a settling section containing five screens and a contraction ratio of 12.25. The test section is octagonal, 1.20 m wide by 1.08 m high. The first 1.2 m of its length is enclosed by acrylic walls, and the last 0.5 m is open, giving unrestricted access. Experiments can be carried out in both the open and closed parts, and comparison between them can potentially be used to measure the lift effect correction. The fan is driven by an a.c. motor with a variable-frequency power supply, allowing the wind speed to be varied continuously from 0 to 38 m s-1. The whole machine can be tilted to give up to 8 ° descent and 6 ° climb. A pitot-static survey in the test section showed that the air speed was within ±1.3 % of the mean at 116 out of 119 sample points, exceeding this deviation at only three points at the edges. A hot-wire anemometer survey showed that the turbulence level in the closed part of the test section was below 0.04 % of the wind speed throughout most of the closed part of the test section, rising to approximately 0.06 % in the middle of the open part. No residual rotation from the fan could be detected in the test section. No decrease in wind speed was detectable beyond 3 cm from the side walls of the closed part, and turbulence was minimal beyond 10 cm from the walls. The installation of a safety net at the entrance to the test section increased the turbulence level by a factor of at least 30, to 1.2 % longitudinally and 1.0 % transversely.

A Novel Vibrating Ribbon Technique

2005 ◽  
Author(s):  
Jonathan H. Watmuff
Keyword(s):  
Test Section ◽  
Vibration Amplitude ◽  
Wave Amplitude ◽  
Separation Bubble ◽  
Wind Tunnel Test ◽  
Mean Flow ◽  
Test Plate ◽  
Numerical Predictions ◽  
The Mean

A novel vibrating ribbon apparatus is described that is active over the full span of a wind tunnel test section. The spanwise uniformity of the vibration amplitude and other ribbon characteristics are considered in detail. The height of each end of the ribbon above the test plate can be adjusted in situ, while the ribbon is vibrating and with flow in the test section, thereby allowing the response of the layer to be easily tuned. The growth of the wave amplitude downstream of the ribbon is shown to agree with numerical predictions. However, two or three wavelengths of development are required before the wave amplitude follows the predicted growth. The flow around an inactive ribbon is examined using a commercial CFD solver and features such as a miniature separation bubble just downstream of the ribbon are revealed. The distance required for the mean flow to recover from the disturbance introduced by the ribbon is greater when the ribbon is located further from the wall. The mean flow recovers to form a boundary layer that is slightly thicker than the undisturbed flow. Experimental measurements indicate that the distance required for the wave motions to follow predicted behavior is about 4 or 5 times larger than distance for recovery of the mean flow.

On the stability of an inviscid shear layer which is periodic in space and time

1967 ◽  
Vol 27 (4) ◽  
pp. 657-689 ◽  
Author(s):  
R. E. Kelly
Keyword(s):  
Growth Rate ◽  
Shear Layer ◽  
Finite Amplitude ◽  
Periodic Component ◽  
Periodic Flow ◽  
Flow Profile ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean ◽  
The Stability

In experiments concerning the instability of free shear layers, oscillations have been observed in the downstream flow which have a frequency exactly half that of the dominant oscillation closer to the origin of the layer. The present analysis indicates that the phenomenon is due to a secondary instability associated with the nearly periodic flow which arises from the finite-amplitude growth of the fundamental disturbance.At first, however, the stability of inviscid shear flows, consisting of a non-zero mean component, together with a component periodic in the direction of flow and with time, is investigated fairly generally. It is found that the periodic component can serve as a means by which waves with twice the wavelength of the periodic component can be reinforced. The dependence of the growth rate of the subharmonic wave upon the amplitude of the periodic component is found for the case when the mean flow profile is of the hyperbolic-tangent type. In order that the subharmonic growth rate may exceed that of the most unstable disturbance associated with the mean flow, the amplitude of the streamwise component of the periodic flow is required to be about 12 % of the mean velocity difference across the shear layer. This represents order-of-magnitude agreement with experiment.Other possibilities of interaction between disturbances and the periodic flow are discussed, and the concluding section contains a discussion of the interactions on the basis of the energy equation.

Suppression of background noise in a transonic wind-tunnel test section

AIAA Journal ◽  
1975 ◽  
Vol 13 (11) ◽  
pp. 1467-1471 ◽  
Author(s):  
L. A. Schutzenhofer ◽  
P. W. Howard
Keyword(s):  
Wind Tunnel ◽  
Test Section ◽  
Background Noise ◽  
Wind Tunnel Test ◽  
Transonic Wind Tunnel

Combined effects of flow curvature and rotation on uniformly sheared turbulence

2009 ◽  
Vol 628 ◽  
pp. 371-394 ◽  
Author(s):  
D. C. ROACH ◽  
A. G. L. HOLLOWAY
Keyword(s):  
Shear Stress ◽  
Wind Tunnel ◽  
Model Development ◽  
Three Dimensional ◽  
Simple Shear Flow ◽  
Test Case ◽  
Mean Velocity ◽  
Tunnel Section ◽  
Flow Curvature ◽  
The Mean

This paper describes an experiment in which a uniformly sheared turbulence was subjected to simultaneous streamwise flow curvature and rotation about the streamwise axis. The distortion of the turbulence is complex but well defined and may serve as a test case for turbulence model development. The uniformly sheared turbulence was developed in a straight wind tunnel and then passed into a curved tunnel section. At the start of the curved section the plane of the mean shear was normal to the plane of curvature so as to create a three-dimensional or ‘out of plane’ curvature configuration. On entering the curved tunnel, the flow developed a streamwise mean vorticity that rotated the mean shear about the tunnel centreline through approximately 70°, so that the shear was nearly in the plane of curvature and oriented so as to have a stabilizing effect on the turbulence. Hot wire measurements of the mean velocity, mean vorticity, mean rate of strain and Reynolds stress anisotropy development along the wind tunnel centreline are reported. The observed effect of the mean shear rotation on the turbulence was to diminish the shear stress in the plane normal to the plane of curvature while generating non-zero values of the shear stress in the plane of curvature. A rotating frame was identified for which the measured mean velocity field took the form of a simple shear flow. The turbulence anisotropy was transformed to this frame to estimate the effects of frame rotation on the structure of sheared turbulence.

Wind Tunnel Test of Honeycomb in Improving Flow Quality

2013 ◽  
Vol 774-776 ◽  
pp. 275-278
Author(s):  
Chun Guang Li ◽  
Yang Liu ◽  
John.C.K. Cheung
Keyword(s):  
Wind Tunnel ◽  
Cell Size ◽  
Turbulence Intensity ◽  
Wind Tunnel Test ◽  
Open Loop ◽  
Incoming Flow ◽  
Flow Quality ◽  
The Mean ◽  
Square Cells ◽  
Change Tendency

The function of honeycomb with different length and width in improving flow quality were studied in the course of building a new small section open loop wind tunnel. Instantaneous velocities of turbulent flow in the tunnel were measured by cobra probe. The focus of this study was put on the effect of the honeycomb in attenuating the total turbulence intensity including the free-turbulence carried by the incoming flow and the turbulence generated by the square cells themselves. The change tendency of the mean wind velocity and the total turbulence characteristics in the decay area have been studied by varying the length to cell size ratio L/D, and ratio of distance between the square cells and the measuring position to cell size X/D.

Design of a Wind Tunnel Test Section for Single Airfoil Configuration With Real-Time Lift Force Control

2017 ◽  
Author(s):  
Aline Aguiar da Franca ◽  
Dirk Abel
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Real Time ◽  
Force Control ◽  
Test Section ◽  
Lift Force ◽  
Angle Of Attack ◽  
Wind Tunnel Test ◽  
Wiener Model ◽  
Dynamic Matrix

This article presents a concept of test section for a closed-return wind tunnel, where the lift force of an airfoil, which depends on the angle of attack, is controlled in real-time. This airfoil is used to represent a wind turbine blade. The lift force of the blades is what produces the rotor torque of the wind turbine. This torque determines the amount of energy that will be captured by the wind turbine. The linear dynamics of the motor used to change the angle of attack and the static non-linearity of the airfoil are modeled as a Wiener model. The Quadratic Dynamic Matrix Controller based on Wiener model with linearizing pre-compensation is implemented to keep the lift force constant, which is desirable to avoid mechanical loads for wind turbine applications.

Sign in / Sign up

Export Citation Format

Share Document