scholarly journals The effect of wind tunnel interference on the characteristics of an aerofoil

1930 ◽  
Vol 129 (809) ◽  
pp. 135-145 ◽  
Keyword(s):  
Wind Tunnel ◽  
Uniform Distribution ◽  
Infinite Series ◽  
Rectangular Channel ◽  
Approximate Expression ◽  
Point Of View ◽  
Approximate Methods ◽  
Free Jet ◽  
Drag And Lift ◽  
Lift And Drag

The effect of the walls of the enclosure on the measured values of the lift and drag experienced by an aerofoil is quite appreciable and it has been known for a considerable time that correction must be applied to wind tunnel result before they can be applied to free air conditions. Prandtl* investigated the effect on an aerofoil in a free jet or circular tube both in the case where there is a uniform lift distribution, and in the case where there is an elliptic distribution of circulation. The elliptic distribution is of importance because it gives the minimum drag for a given lift. Glauert by means of an approximate method found the induced drag and lift in a rectangular channel when there is a uniform distribution of lift. Terazawa modified Glauert’s method and obtained the exact solution for an aerofoil with uniform distribution of circulation in a rectangular channel. It is The object of this note to extend these results and to obtain the induces drag and lift in a rectangular channel when there is an elliptic distribution of lift. In addition, the discussion of Prandtl is briefly gone through because Prandtl’s results are usually given as the first few terms of an infinite series, and it has not been noticed that the result can be obtained exactly. Glauert’s work on the effect of plane barries is briefly re-examined because, in his analysis, approximate expression were summed over an infinite series of points, and at first glance it appeared that this would introduce some error of the same order as the result. In this note the summation is carried out rigorously and the approximations to the actual values. The small divergences from Glauert’s result obtained by Terazawa in two numerical cases are, in effect, the result of a slightly more accurate approximation. From the practical point of view the results of this paper add little to what is known already, for the major corrections are given by the results of the approximate methods, but this note should fill in some small gaps in the theory of wind tunnel interference.

scholarly journals The aerofoil in a wind tunnel of elliptic section

1933 ◽  
Vol 140 (842) ◽  
pp. 579-604 ◽  
Keyword(s):  
Boundary Condition ◽  
Wind Tunnel ◽  
Uniform Distribution ◽  
Rectangular Channel ◽  
Circular Section ◽  
Free Jet ◽  
Free Air ◽  
Trailing Vortices ◽  
Elliptic Section ◽  
Lift And Drag

The lift and drag experienced by an aerofoil in a wind tunnel differ from the lift and drag experienced by the same aerofoil under free air conditions. These differences, which are the induced effects due to the walls of the enclosure, can be determined by the aid of general considerations laid down by Prandtl. In a closed tunnel, that is, a tunnel with rigid walls, the necessary boundary condition is that the velocity normal to the walls shall be zero. In an open tunnel, or free jet, the condition is that the pressure is constant over the boundary. Assuming that trailing vortices spring from the aerofoil and extend downstream without distortion, Prandtl has shown that the problem can be converted into one dealing with the flow in a section of the wake far behind the aerofoil, the necessary boundary condition being that the velocity potential is constant over the trace of the open tunnel. Prandtl ( loc. cit .) himself has investigated the interference experienced by an aerofoil in a tunnel of circular section for an elliptic distribution of lift across the span. Glauert, to whom a considerable extension of the theory is due, found approximate values of the induced drag in a rectangular tunnel when the span of the aerofoil is indefinitely small. Terazawa modified Glauert’s method and obtained the exact solution for an aerofoil with uniform distribution of circulation in a rectangular channel. Rosenhead obtained exact results for uniform and elliptic distributions both in circular and rectangular tunnels. More recently, in connection with the building of a wind tunnel of elliptic section, Glauert was led to reconsider the general problem of wind tunnel interference, and his conclusions are embodied in three valuable papers. In the first of these he pointed out that the problem discussed by previous investigators is that in which the lift distribution is prescribed to be the same as that in free air, and the aerofoil is twisted in the tunnel to a position in which this distribution is maintained. In general, if the aerofoil is not twisted in this way, there is a change in the distribution of circulation. If this change is taken into account, Glauert has shown for a tunnel of circular section “that the formulæ derived from the assumption of elliptic distribution of lift are sufficiently accurate for all conventional shapes of aerofoil, but that those derived from the assumption of a uniform distribution over-estimate the effect of increasing span of the aerofoil.”

Analysis of lift and drag coefficients of a GT2 racing car at various speeds with movable wheels and ground

2015 ◽  
Vol 12 (3) ◽  
pp. 261-270
Author(s):  
Albert Boretti
Keyword(s):  
Wind Tunnel ◽  
Drag Force ◽  
Computational Fluid Dynamic ◽  
Lift Force ◽  
Fluid Dynamic ◽  
Time Simulation ◽  
Rear Wing ◽  
Speed Range ◽  
Drag And Lift ◽  
Lift And Drag

The paper proposes a study of a GT2 racing car with a computational fluid dynamic (CFD) tool. Results of STAR-CCM+ simulations of the flow around the car in a wind tunnel with movable ground and wheels are presented for different air speeds to assess the different contributions of pressure and shear to lift and drag over the speed range. The rear wing contributes more than 85% of the lift force and 7-8% of the drag force for this particular class of racing cars. When reference is made to the low speed drag and lift coefficients, increasing the speed from 25 to 100 m/s produces an increase of CD of more than 3% and a reduction of CL of more than 2%. The resultsuggests modifying the constant CD and CL values used in lap time simulation toolsintroducing the tabulated values to interpolate vs. the speed of the car.

Drag and lift measurements of solid sports balls in still air

2017 ◽  
Vol 232 (3) ◽  
pp. 255-263 ◽  
Author(s):  
Jeff R Kensrud ◽  
Lloyd V Smith
Keyword(s):  
Surface Roughness ◽  
Wind Tunnel ◽  
Drag Coefficient ◽  
Rough Surface ◽  
Lift Coefficient ◽  
Laboratory Setting ◽  
Air Drag ◽  
High Speeds ◽  
Drag And Lift ◽  
Lift And Drag

The following article considers lift and drag measurements of solid sports balls propelled through still air in a laboratory setting. The balls traveled at speeds ranging from 26 to 134 m/s with spin rates up to 3900 r/min. Light gates measured the speed and location of the balls at two locations from which lift and drag values were determined. Ball roughness varied from polished to rough surface protrusions, that is, seams as high as 1.5 mm. Lift and drag were observed to depend on speed, spin rate, surface roughness, and seam orientation. A drag crisis was observed on smooth balls as well as non-rotating seamed balls with seam heights less than 0.9 mm. The drag coefficient of approximately 0.42 was nearly constant with speed for spinning seamed balls with seam height greater than 0.9 mm. The still air drag coefficient of smooth balls was comparable to wind tunnel drag at low speeds ( Re < 2 × 105) and higher than wind tunnel results at high speeds ( Re > 2 × 105). The lift and drag coefficients of spinning balls increased with increasing spin rate. The lift coefficient of baseballs was not sensitive to ball orientation or seam height.

Experimental and Numerical Analysis of Lift and Drag Force of Sedan Car Spoiler

2012 ◽  
Vol 165 ◽  
pp. 43-47 ◽  
Author(s):  
A.R. Norwazan ◽  
A.J. Khalid ◽  
A.K. Zulkiffli ◽  
O. Nadia ◽  
M.N. Fuad
Keyword(s):  
Fluid Dynamics ◽  
Wind Tunnel Test ◽  
Point Of View ◽  
Cfd Analysis ◽  
Baseline Model ◽  
Different Types ◽  
Rear Spoiler ◽  
Computational Fluid Dynamics Cfd ◽  
Drag And Lift ◽  
Lift And Drag

Nowadays, the spoiler is fitted at the rear car to make the car looks sporty without taking any consideration to its shape and aerodynamic. This paper carried out other benefits of the rear spoiler respective to the engineering point of view. These study concerns about drag and lift forces were produced by spoiler using wind tunnel test and simulation computational fluid dynamics (CFD) analysis. The main objective of this project is to compare the performances between the two methods in order to determine the aerodynamics performance of three different types of spoiler. The results of CLand CDhave been determined and compared for all the three spoilers including the baseline model as a reference. The result shows that the comparisons of all models have different value of CLand CDbut the model of spoiler 3 is more than 5%.

An Experimental and Numerical Assessment of Airfoil Polars for Use in Darrieus Wind Turbines: Part 2 — Post-Stall Data Extrapolation Methods

2015 ◽  
Author(s):  
Alessandro Bianchini ◽  
Francesco Balduzzi ◽  
John M. Rainbird ◽  
Joaquim Peiro ◽  
J. Michael R. Graham ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Full Range ◽  
Vertical Axis ◽  
Wind Tunnel Tests ◽  
Numerical Assessment ◽  
Wide Range ◽  
Naca0018 Airfoil ◽  
Lift And Drag ◽  
Data Extrapolation

Accurate post-stall airfoil data extending to a full range of incidences between −180° to +180° is important to the analysis of Darrieus vertical-axis wind turbines (VAWTs) since the blades experience a wide range of angles of attack, particularly at the low tip-speed ratios encountered during startup. Due to the scarcity of existing data extending much past stall, and the difficulties associated with obtaining post-stall data by experimental or numerical means, wide use is made of simple models of post-stall lift and drag coefficients in wind turbine modeling (through, for example, BEM codes). Most of these models assume post-stall performance to be virtually independent of profile shape. In this study, wind tunnel tests were carried out on a standard NACA0018 airfoil and a NACA 0018 conformally transformed to mimic the “virtual camber” effect imparted on a blade in a VAWT with a chord-to-radius ratio c/R of 0.25. Unsteady CFD results were taken for the same airfoils both at stationary angles of attack and at angles of attack resulting from a slow VAWT-like motion in an oncoming flow, the latter to better replicate the transient conditions experienced by VAWT blades. Excellent agreement was obtained between the wind tunnel tests and the CFD computations for both the symmetrical and cambered airfoils. Results for both airfoils also compare favorably to earlier studies of similar profiles. Finally, the suitability of different models for post-stall airfoil performance extrapolation, including those of Viterna-Corrigan, Montgomerie and Kirke, was analyzed and discussed.

Vibration Excitation Forces in a Normal Triangular Tube Bundle Subjected to Two-Phase Cross Flow

2011 ◽  
Author(s):  
E. S. Perrot ◽  
N. W. Mureithi ◽  
M. J. Pettigrew ◽  
G. Ricciardi
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Random Excitation ◽  
Two Phase ◽  
Constant Frequency ◽  
Fluid Forces ◽  
Drag Forces ◽  
Wide Range ◽  
Drag And Lift ◽  
Lift And Drag

This paper presents test results of vibration forces in a normal triangular tube bundle subjected to air-water cross-flow. The dynamic lift and drag forces were measured with strain gage instrumented cylinders. The array has a pitch-to-diameter ratio of 1.5, and the tube diameter is 38 mm. A wide range of void fraction and fluid velocities were tested. The experiments revealed significant forces in both the drag and lift directions. Constant frequency and quasi-periodic fluid forces were found in addition to random excitation. These forces were analyzed and characterized to understand their origins. The forces were found to be dependent on the position of the cylinder within the bundle. The results are compared with those obtained with flexible cylinders in the same tube bundle and to those for a rotated triangular tube bundle. These comparisons reveal the influence of quasi-periodic forces on tube motions.

scholarly journals A unified method of identification and optimization of airfoils for aircrafts, turbine and compressor blades

2016 ◽  
Vol 2 (3(4)) ◽  
pp. 2
Author(s):  
Stanisław Ziętarski ◽  
Stanisław Kachel ◽  
Adam Kozakiewicz
Keyword(s):  
Wind Tunnel ◽  
Gas Flow ◽  
Parametric Design ◽  
Research Work ◽  
Integrated System ◽  
Turbine Engines ◽  
Compressor Blades ◽  
Specialized Software ◽  
Develop Software ◽  
Lift And Drag

Topics below are rather undesired, but important, outcome not yet completed research on the aircraft airfoils, turbine and compressor blades, parametric design of airfoils, establishing the relationships based on the results of experiments in a wind tunnel, developing databases for determining the relationships between airfoil parameters and lift and drag coefficients. Reliable database created as a result of the research work allows to simulate the wind tunnel. Very early on, however, was necessary to extend the developed specialized software for a new applications, and it meant the need for generalization of software, e.g. for gas turbine engines, propellers, etc. But after some time it turned out, that in order to achieve the required accuracy, the changes are needed in the underlying assumptions, set decades ago. In addition, coordinate measuring machines and systems, and associated software were not always as accurate as expected. Concepts how to solve it and develop software carrying out these tasks are presented in the article. It is like to withdraw from the old path and look for a new path that will lead to the reliable data base. Processes related to air or gas flow should be similarly defined in all the specialized software applications (e.g. aircrafts and turbine engines). Accuracy (10-9 mm) achieved in virtual measurements within the integrated system can be used to verify the results of CMM and other measuring systems, provided that an appropriate software has been developed.

Prediction of drag and lift forces of a high-speed vessel at full scale by CFD-based GEOSIM method

2022 ◽  
pp. 147509022110707
Author(s):  
Ugur Can ◽  
Sakir Bal
Keyword(s):  
High Speed ◽  
Full Scale ◽  
Navier Stokes ◽  
Drag Forces ◽  
Fluid Body ◽  
Unsteady Rans ◽  
Lift Forces ◽  
Drag And Lift ◽  
Lift And Drag ◽  
Model Family

In this study, it was aimed to obtain an accurate extrapolation method to compute lift and drag forces of high-speed vessels at full-scale by using CFD (Computational Fluid Dynamics) based GEOSIM (GEOmetrically SIMilar) method which is valid for both fully planing and semi-planing regimes. Athena R/V 5365 bare hull form with a skeg which is a semi-displacement type of high-speed vessel was selected with a model family for hydrodynamic analyses under captive and free to sinkage/trim conditions. Total drag and lift forces have been computed for a generated GEOSIM family of this form at three different model scales and full-scale for Fr = 0.8 by an unsteady RANS (Reynolds Averaged Navier–Stokes) solver. k–ε turbulence model was used to simulate the turbulent flow around the hulls, and both DFBI (Dynamic Fluid Body Interaction) and overset mesh technique were carried out to model the heave and pitch motions under free to sinkage/trim condition. The computational results of the model family were used to get “drag-lift ratio curve” for Athena hull at a fixed Fr number and so the corresponding results at full scale were predicted by extrapolating those of model scales in the form of a non-dimensional ratios of drag-lift forces. Then the extrapolated full-scale results calculated by modified GEOSIM method were compared with those of full-scale CFD and obtained by Froude extrapolation technique. The modified GEOSIM method has been found to be successful to compute the main forces (lift and drag) acting on high-speed vessels as a single coefficient at full scale. The method also works accurately both under fully and semi-planing conditions.

Introduction

2003 ◽  
Keyword(s):  
Molecular Dynamics ◽  
Computational Chemistry ◽  
Mathematical Theory ◽  
Fundamental Equation ◽  
Point Of View ◽  
Scaling Relations ◽  
Approximate Methods ◽  
Computational Speed ◽  
Diverse Field ◽  
Physical Laws

Molecular dynamics deals with the motion of and the reaction between atoms and molecules. The fundamental theory for the description of essentially all aspects of the area has been known and defined through the non-relativistic Schrdinger equation since 1926. The “only” problem, therefore, is the solution of this fundamental equation. Unfortunately, this solution is not straightforward and, as early as 1929, prompted the following remark by Dirac (1929). . . The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the application of these laws leads to equations much too complicated to be soluble. . . . Dirac could, for that matter, have added the area of molecular biochemistry. But here the systems become even bigger and therefore the above statement is even more correct. What neither Dirac nor anybody else at that time could foresee was the invention of the computer. With that, a whole new area, namely that of computational chemistry, was created. The recent five-volume work Encyclopedia of Computational Chemistry (1998[1]), with several hundred entries, bears witness to the tremendous evolution in this particular area over the last fifty years or so. The success of computational chemistry has to do not only with computers and the increase in computational speed but also with the development of new methods. Here again it should be emphasized that the availability of computers makes the construction of approximate methods a very rich and diverse field with many possibilities. Thus, this combination of computer power and the invention of theoretical and computational methods has changed the pessimistic point of view into an optimistic one. To quote Clementi (1972), “We can calculate everything.” Although this statement, at least in 1972, was somewhat optimistic, development since then has shown that the attitude should be quite optimistic. The purpose of approximate methods should be, and always is, to try to circumvent the bad scaling relations of quantum mechanics.

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