Wind Tunnel

MECHANICAL ENGINEERING (SEM 7)Vadodara Institute of Engineering, Kotambi

FLOW VISUALIZATION IN WIND TUNNEL FOR

ANALYSSI OF AERODYNAMIC SHAPE

ANALYSISPrepared By:Hardik PatelRoll No:11me03Dhruv PatelRoll No:11me20Priyam PatelRoll No:11ME21Hardik PathakRoll No:11me59

Guided By:Mr. Ravish Patel

Flow visualization is a technique in experimental fluid mechanics that renders certain properties of a flow field directly accessible to visual perception. In general and under normal circumstances, most fluids, gaseous or liquid, are transparent media, and their motion must remain invisible to the human eye during direct observation, unless a technique allowing visualization of the flow is applied. The technique of marking flow lines or structures in an air stream by means of smoke is, in principle, the same as visualizing the flow pattern of a liquid by the injection of dye. Although it is application is not restricted to wind tunnels, smoke visualization is a standard experimental tool for these facilities, and its technical advancement is closely related to the history of wind tunnels. This final year project is intended to design and fabricate a wind tunnel equipped with smoke flow visualization facility for the experimental research at our institute’s Fluid Mechanics Laboratory. The aim is to make a 2-dimensional flow visualization set-up, which can aid for experiments related to flow over various 2D test profiles. The term ‘smoke’ can be used in a wide sense. It is not only restricted to combustion products, but can also include steam, vapour, aerosols and mist. Desired properties for a tracer are neutral buoyancy, stability against mixing, etc. Considering the economics, ease of use and availability, kerosene has been selected to generate smoke. In this project, we will study about effect of air and the values of lift and drag over an airfoil and cylinder at different angle of attack.

ABSTRACT

LITERATURE REVIEW

INTRODUCTION

SMOKE VISUALIZATION TCHNIQUE

DESIGN CALCULATION AND DESIGN

EXPECTED OUTCOME

OUTLINE

1. Design of Various Components of Open Circuit Wind Tunnel RanjanBasak and DebojyotiMitra stated that a wind tunnel is an essential tool in engineering, both for model tests and basic research. To ensure a controlled return flow, most of the tunnels are designed as a closed circuit type. However, it is possible to achieve high performance from an open circuit tunnel, therefore saving space and construction cost. For easy of changing the working section the exit diffuser is often omitted from open circuit blower tunnels at the cost of power factor greater than unity. In this paper detail design procedure is discussed for open circuit blower tunnel without exit diffuser. The aerodynamic design of open circuit wind tunnel driven by a centrifugal blower connected to the settling chamber by a wide angle diffuser is discussed. The design or choice of blower, diffuser, screens, contraction and working section are described here. They have a strong influence on tunnel performance. The design rules and suggestions are mainly based on data collected from successful blower tunnel design. The design of blower driven wind tunnel is a combination of arts, science and common sense, the last being the essential. It is difficult and unwise to predict firm rules for tunnel design. This is mainly due to the wide variety of tunnel design and the lack of understanding of the flow through wind tunnel components like diffuser, screen and blower itself. It is more feasible and sensible to predict design boundaries based on the data from existing tunnels which are known to perform satisfactorily.

LITERATURE REVIEW

2. Flow Visualization in Wind TunnelMuzafferuddinMahmood stated that Flow visualization is an experimental means of examining the flow patterns around a body or over its surface. The flow is “visualized” by introducing dye, smoke or pigment into the flow in the area under investigation. The primary advantage of such a method is its ability to provide a description of the flow over a model without a complicated data reduction and analysis. Smoke- flow visualization (described by Bradshaw, 1970 and Rae and Pope 1984) involves the injection of streams of vapour into the flow. The vapour follows filament lines (lines made up of all the fluid particles passing through the injection points) in steady flow the filament lines are identical to stream lines. (Lines everywhere tangent to the velocity vector). Smoke- flow visualization thus reveals the entire flow pattern around a body. It is difficult to exaggerate the value of flow visualization. The ability to see flow pattern on a model often gives insight into a solution to an aerodynamic problem. Flow visualization can be divided into two broad categories the first is surface flow visualization when the visualization media is applied to the surface such as tufts and oil flow etc.

The second type is off surface such as smoke and streams.There are basically four methods of recording the flow visualization test are showed above.Because of the depth perception one can see a three dimensional picture. The other three common methods of recording the result of flow visualization are by film, either still or movie or television camera or video and magnetic tapes. It must be realized that all three of these methods are using a two dimensional medium to often record a three dimensional phenomena. This is especially fine when using a smoke or helium bubbles to trace flow stream lines pass the model. All three of these methods can be used either black and white or color. The photography methods while recording more time for developing and printing stills, when compared to video, yield higher resolution.

3. CFD AnalysisSelviRajan ,Santhoshkumar., LakshmananIn order to understand the physical phenomena of the wind flow over the typical launch vehicle, the flow was simulated using both Wind tunnel and Computational Fluid Dynamics (CFD). In the present study, tests were conducted on a 1:50 scaled model of a launch vehicle. The model was subjected to two wind conditions, wind flow normal to the shorter plan dimension = 0 , where the three main cylinders of the model were one behind the other and wind flow normal to the longer plan dimension, = 90 , where all the three main cylinders of the vehicle are subjected to direct wind pressure in the windward direction. Based on the CFD studies, the flow pattern and the force coefficients were derived. To validate these results, wind tunnel tests were carried out on a 1:50 scaled rigid and light-weight models respectively, for obtaining path lines and force coefficients. Results on streamlines obtained based on CFD simulation and wind tunnel experiments compared very well. The force coefficients in both directions were evaluated from CFD results showed good agreement with the corresponding measured values based on wind tunnel experiment.

4. Performance Analysis on Airfoil Model in Wind Tunnel Testing Machine (WTTM)A Wind Tunnel Testing Machine (WTTM) is a tool used in Aerodynamic research to study the effects of Air moving past to the solid objects. A wind tunnel testing machine consists of a closed tubular passage with the object under test mounted in the middle and powerful fan system moves air past to the object. The wing (airfoil) provides lift by creating a situation where the pressure above the wing is lower than the pressure below the wing. Since the pressure below the wing is higher than the pressure above the wing. The readings has been taken on airfoil model in Wind Tunnel Testing Machine (WTTM) at different air velocity 20m/sec, 25m/sec, 30m/sec and different angle of attack 00,50,100,150,200. Air velocity and pressures are measured in several ways in wind tunnel testing machine by use to measuring instruments like Anemometer and Multi tube manometer. The Surface roughness of an airfoil is can be measure by Surface roughness tester. The heat signature of a testing model is can be measure by Thermal Imaging Camera. The CFD analysis is also carried out at various sections of airfoil angles and velocity. The maximum performance to the airfoil model is achieved at 100 on angle of attack.

5. The wind tunnel performance investigation by using the modeling and simulation“The wind tunnel is considered as an important device to test the aerodynamic performance of the different bodies, the function of it is to imitate the controlled wind speed of optimal environment that facing the model for unlimited time to obtain the aerodynamic steady-state experimental results. The wind tunnel performance depends on the characteristic of the air stream passing through test-section, the aim of this research is to investigate the viability of the wind tunnel that exist in the gas- dynamic laboratory of the Damascus university, by comparison the experimental results as forces and coefficients of lift and drag for three difference types of the airfoils (NACA6410, Sg6043, NACA7308) with the results of the advanced program specific for design and define the airfoil characteristic which called (Design Foil R6) prepared by Illinois university.”

6. Analysis of Aerofoil Blade using ANSYS for a Vehicle Mounted Micro Wind Turbine“Energy is the primary and most universal measure of all kinds of work by human beings and nature. Everything that happens in the world is an expression of energy in one of its forms. “Energy can neither be created nor be destroyed. It can only be converted from one form into another”. So can wind energy be converted from one form to another? Wind energy is readily converted into mechanical energy through theturbine blades and is further converted into electrical energy by connecting the turbine to an electrical generator. In this paper we analyze the aerofoil cross section blade using ANSYS 10.0 and show the velocity profile for a blade which is positioned parallel to the flow of wind and another blade which is tilted at a certain angle to the flow of the wind. This paper also visualizes the use of a variable geometry blade to minimize the drag when the wind flows over the blade.”

7. CFD Analysis of Pressure Coefficient for NACA 4412Wind Turbine“In this paper NACA 4412 airfoil profile is considered for analysis of wind turbine blade. Geometry of the airfoil is created using GAMBIT 2.4.6. And CFD analysis is carried out using FLUENT 6.3.26 at various angles of attack from 0˚ to 12˚. Variations of pressure coefficient are plotted in form of contour for1 ×105 Reynolds number.” 8. Computational Design and Analysis of Flatback Airfoil Wind Tunnel Experiment“A computational fluid dynamics study of thick wind turbine section shapes in the test section of the UC Davis wind tunnel at a chord Reynolds number of one million is presented. The goals of this study are to validate standard wind tunnel wall corrections for high solid blockage conditions and to reaffirm the favorable effect of a blunt trailing edge or flat back on the performance characteristics of a representative thick airfoil shape prior to building the wind tunnel models and conducting the experiment. The numericalSimulations prove the standard wind tunnel corrections to be largely valid for the proposed test of 40% maximum thickness to chord ratio airfoils at a solid blockage ratio of 10%. Comparison of the computed lift characteristics of a sharp trailing edge baseline airfoil and derived flat back airfoils reaffirms the earlier observed trend of reduced sensitivity to surface contamination with increasing trailing edge thickness.”

9. ANSYS Workbench Tutorial – Flow Over an Airfoil“This tutorial provides instructions for creating a fluid volume and mesh around a NACA 4314 airfoil and for analysing the flow in FLUENT. It also shows how to use multiple fluid bodies and edge sizing to create a “c-mesh”. The entire meshed fluid field and a portion of the mesh near the airfoil are shown below.”

INTRODUCTION

INTRODUCTION IS DEVIDED IN TWO PARTS

FLOW VISUALIZATION TECHNIQUE WIND TUNNEL

FLOW VISUALIZATION TECHNIQUE

Flow visualization is a technique for examining the flow pattern on object body over its surface and pressure distribution behind the object.

Why it is require?

Most fluids, gaseous or liquid, are transparent media, and their motion remains invisible to the human eye during direct observation. Therefore, techniques allowing visualization of the flow usually referred to as flow visualization need to be developed to understand fluid behavior under different conditions.

The object such as :airfoil cylinder aerodynamic models

Can be tested by this technique.


Flow visualization techniques:Hydrogen Bubble: Using a platinum cathode, hydrogen bubbles are formed using electrolytic method. The size of the bubble formed is approximately 0.1 mm. Illumination causes internal reflections within the bubbles which facilitate the visualization of the flow. This method can completely trace the flow over a body or complex flow field. Smoke flow visualization :

This is one of the oldest methods of flow visualization.Light, non-poisonous, and contaminants-free smoke is injected into the flow through an array of nozzles, which facilitates visualization of flow.

Usually oils, especially kerosene, are used to generate smoke. Oil is heated around its boiling temperature to produced colored smoke.


Sufrace oil flow:Coloured oil flows is used on the surfaces to visualize the flow around the object.

Fog:Fog (wet water particles) is used to visualize the flow.

WIND TUNNEL

A wind tunnel is a tool used in aerodynamic research to study the effects of air moving past solid objects. A wind tunnel consists of a tubular passage with the object under test mounted in the middle. Air is made to move past the object by a powerful fan system or other means.

Wind Tunnel Types:

Based on Design as :

Open type wind tunnel Closed type wind tunnel Aerodynamic wind tunnel Low turbulence wind tunnel

Based on flow speed as:

Subsonic (low speed) wind tunnel Transonic wind tunnel Supersonic wind tunnel Hypersonic wind tunnel

Based on working fan as:

Blower type wind tunnel Suction type wind tunnel

For the experimental purpose low speed wind tunnel is used.

Main Component : Settling Chamber Contraction cone Test Section Diffuser Drive(Exit) Section

Reynolds number (Re) is a dimensionless number that gives a ratio of inertial forces to viscous forces.

Reynolds Number

When Reynolds Number is

Re < 300000 , the flow is called as Laminar flow whereas

Re > 500000, the flow is called as Turbulent flow.

Mach Number (Ma) is a dimensionless quantity representing the ratio of

speed of an object moving through a fluid and the local speed of sound.

Following are the range of mach number.

For subsonic wind tunnel mach number should be less

than 0.8.

Mach Number (Ma) is a dimensionless quantity representing the ratio of

speed of an object moving through a fluid and the local speed of sound.

Following are the range of mach number.

For subsonic wind tunnel mach number should be less

than 0.8.

Main component of Wind tunnel: Blower Settling chamber Contraction Cone Test Section Diffusor section

DESIGNCALCULATION AND DESIGN

Blower:

Centrifugal blower is used to get desire air flow.

Centrifugal blower is almost always of the backward-airfoil or squirrel-cage

type. These blowers are usually made of cast metal.


Settling Chamber: The settling chamber straightens the airflow. The settling chamber usually includes a honeycomb flow

straightener and wire mesh smoothing screens that produce a smooth airflow

The honeycomb structure of a settling chamber is very effective at reducing swirling currents in the tunnel airflow.


Contraction Cone: The contraction or "nozzle" accelerates the flow from the settling

chamber into the test section.


Test Section: The object, flow past which is to be observed is placed in the

section. If the diffuser, the settling chamber and the contracting section are designed properly the test section will have uniform velocity at every point in test section.

Cross section = 50 x 50 cm2

Length= 75 cm


Diffuser Section: A diffuser in which the cross-sectional area increases so rapidly that

separation can be avoided only by using boundary layer control.


MODELING OF WIND TUNNEL

MODELING OF WIND TUNNEL

EXPECTED OUTCOME Mechanics Laboratory has been appreciated in terms of its potential to help

understand flow and its effect over various profiles. Pressure interactions in the form of lift and drag, and observing qualitative

flow properties like flow separation. Circulations and vortices, etc. Smoke has been selected for flow visualization

in the setup. Various techniques of flow visualization for experiment purpose have been

studied and analyzed. Fabrication of the wind tunnel has been completed according to the design. Experiments have been carried out on various objects and results have been

analyzed. A numerical simulation of flow past similar bodies using CFD software

developed and has been carried out. In this project, students will study about the effect of air and the values of lift

and drag over an airfoil and cylinder at different angle of attack. Efficient measurement of flow visualization. Also we can easy to understand about smoke generation and stream line.

Documents

Wind Tunnel