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A wind tunnel study was performed on the FFA-W-3-270 airfoil, which form a segment of a 1.25 MW wind turbine blade, to examine the effect of fixed roughness height and position using a zigzag tape boundary layer trip strip. Tests were conducted at a Reynolds number of 1×106 over a wide range of angles of attack. The zigzag tape, as an artificial roughness device, not only triggers a premature transition in the flow whereby laminar flow regimes change to turbulent, but also increases the momentum thickness of the turbulent boundary layer and change the airfoil camber. The 60° zigzag tape of 0.5 mm and 1 mm height was placed on the suction side of the airfoil at different chord wise locations.... 

The original version of this article unfortunately contained a mistake. The affiliation of the second author was incorrect. The correct information is given below: Hadi Ghaebi, Department of Mechanical Engineering, Faculty of Engineering, University of Mohaghegh Ardabili, P.O. Box 179, Ardabil, Iran. © 2018, The Brazilian Society of Mechanical Sciences and Engineering  

Wake analysis plays a significant role in wind-farm planning through the evaluation of losses and energy yield. Wind-tunnel tests for wake studies have high costs and are time-consuming. Therefore, computational fluid dynamics (CFD) emerges as an efficient alternative. An especially attractive approach is based on the solution of the Reynolds-averaged Navier–Stokes (RANS) equations with two-equation turbulence closure models. The validity of this approach and its inherent limitations, however, remain to be fully understood. To this end, detailed wind-tunnel experiments in the wake of a NACA4412 wing section profile are compared with CFD results. Two-and three-dimensional RANS simulations are... 

An existing operational trisonic wind tunnel is upgraded to improve its performance criterion in the transonic regime. In this research, the test section is modified according to the operational requirements of the various existing transonic wind tunnels. Several perforated walls are designed, manufactured, and installed on the top and bottom sides of the test section. The flow in the test section of the wind tunnel is surveyed for the empty condition prior to testing models. Once satisfactory results regarding the flow quality requirements in the test section under various conditions were achieved, a 2D model, NACA 0012, and a 3D standard model for the transonic wind tunnels, AGARD-B, are... 

Experiments are performed to evaluate the impact of trip wires on the turbulence intensity in a few low speed wind tunnels. Trip wires of different sizes are installed at different positions in the contraction section of four different wind tunnels and measurements are made at various free stream velocities. The results indicate that the pressure distributions are altered compared to the clean condition. Trip wires move the adverse pressure gradient toward the inlet of the contraction section. Consequently, the turbulence intensity in the test section of the wind tunnels is reduced and the flow uniformity is improved considerably. Frequency and statistical analysis are performed and the... 

The boundary-layer control authority of a DBD plasma actuator using surface mounted hot-film sensors is evaluated. Wind tunnel experiments on a wind-turbine blade section were established at a Reynolds number of 0.27 x 106. Aerodynamic performance of the wind-turbine blade section for both plasma-ON and plasma-OFF modes are evaluated using measurements made by both surface pressure and wake survey behind the model. Two distinct boundary-layer states are recognized. A state which occurs at the onset and in proximity of the deep stall, which is affected by the low-frequency instabilities of the separated flow. In this case, the steady actuation of plasma imparts local momentum on the nearby... 

This paper deals with design and analysis of intermittent supersonic wind tunnels. System can be constructed by allowing air at atmospheric pressure to pass through a converging-diverging nozzle, a test section and a diffuser into a vacuum tank. The governing equations of compressible fluid flow have been solved numerically using flux vector splitting method to obtain running time under which it works at the design Mach number. The formulation has been tested on the theory of quasi one-dimensional compressible flow. The numerical results are in good agreement with the results of the theory  

In this investigation an intensive experimental study was conducted to study the flow quality in a test section of a low speed, V∞ = 10 - 100, closed return wind tunnel. An interesting result was obtained when a trip strip, a guitar wire with D= 1.14mm, was installed near the end of the contraction region. Addition of this trip wire resulted in a turbulent reduction almost at all speed ranges along the entire test section. Further, it smoothness the variation of turbulent intensity along the test section too. Velocity profiles along the tunnel wall at various speeds using a rake were measured with and without the trip wire. In addition, pressure contours at different location of the test... 

In this paper, a new approach based on a Generalized Regression Neural Network (GRNN) has been proposed to predict the unsteady forces and moments on a 70° swept wing undergoing sinusoidal pitching motion. Extensive wind tunnel results were being used for training the network and for verification of the values predicted by this approach. The Generalized Regression Neural Network (GRNN) has been trained by the aforementioned experimental data and subsequently was used as a prediction tool to determine the unsteady longitudinal forces and moments of the pitching delta wing for various reduced frequencies. The results are in a good agreement with those determined by the previous experimental... 

A series of unsteady low speed wind tunnel tests on a section of a 660 Kw wind turbine blade which is under construction were conducted to examine the effects of distributed surface contamination on its performance characteristics. Model was tested at three mean angles of attack, 5, 10 and 18 degrees at the fixed oscillation domain of 5 degrees. Results show that contamination decreases the maximum lift coefficient more than 40 percent. However Reynolds number and oscillation frequency increase, have a positive effect on the maximum lift coefficient in the contaminated model and it decreased the difference between maximum lift coefficient in the clean airfoil and the contaminated one  

Extensive low speed wind tunnel experiments have been undertaken to measure the test section, oor wall pressure distribution, in the presence of a 2D wing inside the test section. The experiments were performed for both the static and dynamic pitching motion of the model under difierent conditions. In these measurements, the efiects of the existence and oscillations of a 2D wing on the oor wall pressure at various locations were studied. According to the results, as the oscillation parameters, such as mean angle of attack and frequency, change, wall pressures at the points located in the front part of the test section, in the upstream region, exhibit difierent behavior from those in the... 

In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon, and the results indicate that the trip strip has significant effects on sound reduction. The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction. Furthermore, the effect of monopole, dipole and quad- rupole sources of aerodynamic noise... 

In this research, the employment of an innovative but simple and cost effective method for turbulent reduction in a low speed wind tunnel is investigated and the effect of this turbulence reduction on the Power Spectrum and FFT-Based signals that obtained from Hot-wire Anemometry is studied. These terms represents the amount of power contained in the signals. Several situations are studied in this paper. One of these situations is when there are four screens in the settling chamber of the wind tunnel and after that by adding the trip strip in the contraction region of the wind tunnel the tests were repeated. In the next stage, three screens were removed from the settling chamber of the wind... 

Extensive wind tunnel tests have been conducted to investigate effects of turbulence intensity variations on the behavior of a section of a wind turbine blade in an oscillatory motion. Special emphasize was applied on the aerodynamic characteristics when oscillating the model in the vicinity of its static stall angle of attack and in the post stall condition. The model had 0.25m chord and was pitched about its quarter-chord. Data were acquired at various Reynolds number, and reduced frequency. Results show that turbulent intensity has strong effect on the unsteady load coefficients, hence aerodynamic performance of this model. Furthermore, free stream turbulence has different effect on the... 

Extensive experimental tests have been conducted to examine the roughness effects on the aerodynamic performance of a model in an oscillatory motion. All tests were carried out in a 0.8×0.8 m 2 low-speed wind tunnel. The model had 0.25m chord and was pitched about its quarter-chord. Data were acquired at various Reynolds number and reduced frequencies. Surface roughness was applied at two different locations of the model upper surface, leading edge and the point of maximum thickness. Furthermore, tunnel turbulent was varied and all tests were repeated. The results indicate that the width of the hysteresis loop, position of the figure eight shape, slope of the normal force coefficient curve,... 

Abstract: Underwater vehicles when yawed to free stream flow, like submarines in a turning maneuver, produce large vortical separated regions. This vortical flow affects acoustic, body drag, control effectiveness and maneuverability. A suitable way to reduce the effects of this separated flow is to use vortex generators. The main goal of this study is to investigate the effect of the vortex generator on the flow field around a standard underwater model employing the vortex generators by using the oil flow visualization method in wind tunnel only in yaw direction (0° ≤ β ≤ 30° angles of attack, due to the experimental cost) and the CFD method in the pitch direction (0° ≤ α ≤ 30° angles of... 

It is important to understand the flow characteristics and performance of wings for designers who want to have an efficient thrust in a land yacht. In this paper, a comparison of aerodynamic forces obtained by testing the land yacht model in a wind tunnel and by the Velocity Prediction Program (VPP) is presented. The wind tunnel testing of a land yacht is an effective design tool, but at present it is mainly used for VPP validation, which allows for a faster and more efficient design process. The rigid wing land yacht model, which is a radio controlled model, is tested in the national open jet wind tunnel of the Malek Ashtar University of Technology in Iran. The wing data, which is obtained... 

Aspects of pitching and plunging motions on unsteady aerodynamic behavior of an aircraft model were studied. Extensive wind tunnel tests were performed on a standard dynamics model, SDM, oscillating in both pitch and plunge modes. Up to now, there has been little or no result on the plunging behavior of an aircraft or missile as a whole and the present experiments can be considered as one of the first attempts to study the compressible flow field over a model undergoing both pitching and plunging motions. The experiments involved measuring normal force and pitching moment of the model at Mach numbers of 0.4, 0.6 and 1.5 and oscillation frequencies of 1.25, 2.77 and 6.00 Hz. The longitudinal... 

This article presents the result of an analysis to determine the distance that the fuselage of a Flapping Flyer moves up and down when the wing flap and comparison it with experiments that was done on fuselage phenomena during flight of an ornithopters and Winged animals in Wind tunnel. It is suggested that this motion may reduce the efficiency of design, whereas the tendency for fuselage motion may be largely cancelled in the bi plane configuration. The article also answers a question that has puzzled for scientist. Why bodies of winged animals don't move up and down noticeably when they flaps their wing during flight? Finally we offer one solution for reduce this unwanted motion near 50 %... 

A new similarity parameter has been used for analyzing the unsteady aerodynamic, behaviour of vehicles undergoing sinusoidal pitching motion. If this parameter is identical for two unsteady manoeuvres with different reduced frequencies and oscillation amplitudes, the corresponding hysteresis loops of the force and moment collapse on each other, To support and verify this, extensive unsteady wind tunnel tests have been conducted on a standard model, which is a well known fighter type configuration. The acquired data were used to train a certain type of neural network, called the Generalised Regression Neural Network (GRNN), to reduce the number of wind tunnel runs. The scheme, once proved to...