INTRODUCTION
Wind tunnel is an apparatus used to study the flow behaviour and effects of air over the test solid object. In the tunnel, one can control the flow conditions which affect forces on the test object. Through the measurements of the forces on the model, one can predict the forces on the full scale test object. In early days the wind tunnels were used to understand and improve the performance of an aircraft only, but later several things such as, car body, buildings, bridges etc. are also being tested in the wind tunnel.
The following classification of a typical wind tunnel is done on the basis of working speed:
FIG-1: TYPICAL BLOWER DIRVEN LOW SPEED WIND TUNNEL
FIG-2: CAD REPRESENTATION OF BLOWER SECTION OF WIND TUNNEL
FIG-3: CAD REPRESENTATION OF BLOWER DIFFUSER OF WIND TUNNEL
FIG-4: CAD REPRESENTATION OF MESH SECTION OF WIND TUNNEL
FIG-5: CAD REPRESENTATION OF REDUCER OF WIND TUNNEL
FIG-6: CAD REPRESENTATION OF TEST SECTION OF WIND TUNNEL
FIG-7: CAD REPRESENTATION OF EXIT DIFFUSER OF WIND TUNNEL
Assembly setup :
Fig-8: Assembly setup of wind tunnel in our campus IIT Gandhinagar
FIG-9: CAD REPRESENTATION FULL ASSYMBLY OF WIND TUNNEL
FIG-10: 2D DRAFTING OF FULL ASSYMBLY OF WIND TUNNEL
WIND TUNNEL LAB REPORT
Wind tunnel is use as a means of studying air flowing past the solid objects in aerodynamic studies. The wind tunnel is made up of different parts. They consist of Settling Chamber, Contraction cone, test section, diffuser and drive section as shown above. In Test Section, view ports are added in order to see the model inside. The air flow from the drive section and get into settling chamber. Then the air move into contraction cone where the velocity will be increase due to the shape of the cone due to the pressure difference. The high and constant velocity air will then enter the test section where the model is to be tested. After that the air will flow into the diffuser where they will be push into the drive section to circulate.
Procedure
An experiment was conducted to test an aircraft model in order to evaluate the lift and drag forces under different angles of attack. The data were taken at different rpm and angles of attack of the model aircraft. The value of coefficient of lift, the coefficient of drag, lift and drag, and airspeed of the model can be obtained from the computer which is connected to the wind tunnel. By putting all the data into the table, series of graphs can be drawn. Using those data, stalling point of the plane can be calculated and also calculate the changes in drag and lift when the angle of attack increases.
The characteristics of wind, variation of its pressure and speed are the interest of many peoples all around the world. Many people are studying the effects of air moving over or around solid objects and at different speed. They do this in a Wind tunnel. Thus the "Wind tunnel" is a facility, by artificially producing airflow relative to a stationary body that measures aerodynamic force and pressure distribution to simulate with actual conditions.
There has been a lot of interest in the field of aerodynamics in Nepal. Many research works has been done by many institutions. But due to the lack of aerodynamic test equipment effective results were not achieved. Also students’ interest towards this field couldn’t be attracted satisfactorily. This is due to the fact that they don’t find even the basic test equipment to enlighten and strengthen their interests. Thus the country is unable to produce higher qualified manpower in this field.
Proposed project would help any institution or individual to make a wind tunnel of their own and perform the required aerodynamics test.
2.0 TECHNICAL DESCRIPTION AND ITS FUNCTIONAL CHARACTRISTICS:
The probable size of wind tunnel under our design consideration is shown in the figure below:
The dimensions of the wind tunnel may vary while considering the economy and simplicity. The settling chamber consists of honeycomb to minimize turbulence. Provisions for transparent window are there in the test section. And the drive section consists of the axial fan. The wind tunnel is designed to have a wind velocity around 40m/s (144 km/hr) in the test section. To do so a compression ratio of 1:3 is used. This means an axial wind fan of about 36inch blade diameter which can generate a speed of 13.33m/s should be used.
Diffuser
3.0 OBJCTIVES
4.0 LITERATURE REVIEW:
A wind tunnel is a device in which a jet of air or any other suitable gas of uniform properties across the cross section is produced. A wind tunnel simulates the conditions of an aircraft in flight by causing a high-speed stream of air to flow past a model of the aircraft (or part of an aircraft) being tested. This is used for aerodynamically testing the model under the given standard conditions.
All the wind tunnels are generally comprised of the driving unit, a settling chamber, an acceleration duct (either contraction or nozzle) the test section and the diffuser. The driving unit consists of fan, blower or a compressor generally driven by an electric motor. The location of the driving unit depends on the type of the tunnel. The flow from the blower or compressor or a fan is settled in a large chamber called the settling chamber. This is provided with wire gauzes and arrays of honeycombs to straighten the flow and remove irregularities in it. The settling chamber supplies the flow to the contraction. This is carefully designed to accelerate the flow from the settling chamber to the test section velocity with minimum disturbance.
The contraction or the nozzle feeds the test section with suitable jet of uniform velocity. The model to be tested is fixed here with suitable supports. The model is mounted on wires so that lift and drag forces on it can be measured by measuring the tensions in the wire. The paths of the air-stream around the model can also be studied by attaching tufts of wool (which align themselves with the wind direction) to various parts of the model, by injecting thin streams of smoke into the tunnel to render the airflow visible, or by using certain optical devices. A transparent window or strong glass is often provided on one or both the side walls of the test section. Pressures on the model surface are measured through small flush openings in its surface. Forces exerted on the model may be determined from measurement of the airflow upstream and downstream of the model. The diffuser collects the flow from the test section and raises the pressure of the air for discharging it into the atmosphere or the return circuit in case of closed circuit tunnel.
Wind tunnel test is a significant factor in any type of vehicle design, from airplanes including automobiles. It is important in the prediction of forces and moments in sailing. Structural engineers also use aerodynamics, and particularly aero-elasticity, to calculate wind loads in the design of large buildings and bridges. Urban aerodynamics seeks to help town planners and designers improve comfort in outdoor spaces, create urban microclimates and reduce the effects of urban pollution. The field of environmental aerodynamics studies the ways atmospheric circulation and flight mechanics affects ecosystems. The aerodynamics of internal passages is important in heating/ventilation, gas piping, and in automotive engines where detailed flow patterns strongly affect the performance of the engine.
5.0 METHODOLOGY:
The activities from the initiation to the finalization of this project involve some these processes:
Regular check and evaluation study of the progress of the project till that date is done monthly. This helps us to know how we are moving and what changes are desired.
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