25-03-2011, 11:56 AM
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DOOGE
Wind tunnel.ppt (Size: 3.98 MB / Downloads: 288)
SEMINAR ON APPLICATIONS OF WIND TUNNELS IN AEROSPACE AND AUTOMOBILE INDUSTRIES.
WHAT ARE WIND TUNNELS ?
Wind tunnels are research tools developed to assist with studying the effects of air moving over or around solid objects .
This study requires taking into account the Reynolds number and the Mach number.
PARAMETERS AFFECTING AN AIRPLANE
Gravity pulls the plane down toward the ground.
Lift pulls the plane up .
Thrust moves the plane forward.
Drag pushes the plane backwards.
BASIC PARTS OF MODERN OPEN WIND TUNNEL
BASIC PARTS OF CLOSED WIND TUNNEL
WORKING OF WIND TUNNEL
As air enters the settling chamber it Contains a honeycomb flow straightener to generate a smooth air flow.
The purpose of the contraction cone is to take a large volume of low-velocity air and reduce it to a small volume of high-velocity air.
the air enters the test section and is brought to the desired velocity.
The shape of the diffuser causes the air to slow down prior to exhausting or recirculating.
The final section of the wind tunnel is called the drive section. This section provides the force that drives the air through the tunnel.
TYPES OF WIND TUNNELS
Basic architecture (open-circuit, closed-circuit).
According to their speed (subsonic, transonic, supersonic, hypersonic).
According to the air pressure (atmospheric, variable- density), or their size (ordinary ones or full-scale).
Open-loop = The air comes through one end and flows out another.
Closed-loop = The air is not released, but is recirculated through the tunnel.
Subsonic = speeds slower than the speed of sound.
Transonic = speeds between Mach 0 .7 and 1.1.
Supersonic = speeds faster than the speed of sound Mach 1 to 4.
Hypersonic = Speeds at or faster than Mach 5.
Refrigerated = Colder than most, used to test for the effects of icing on aircraft performance.
Full-sized = Can fit a full size aircraft model into its test section.
Scale-sized = Is designed for use by scale models (much smaller in size than the real thing). Usually used to test high speed flight.
Need for Wind Tunnels
Basic Needs; Safety, Economics and Education
Proof of design prior to test flight which puts life and prototype at risk
Education, “hands on” learning and observation of fluids (modeling can only be as accurate as one’s perception and understanding of nature)
Flows around complex structures are presently difficult to model with CFD. Scaled model wind tunnel testing is comparatively easy to setup and research
Scaled testing is more economic than full size testing simply because a full size capable wind tunnel is a few orders of magnitude more expensive than a scaled wind tunnel (simultaneity with Reynolds numbers)
9’ x 15’ Low Speed Wind Tunnel at NASA Glenn Research Center
Characteristics and Performance
Test Section Size: 9 ft high by 15 ft wide by 28 ft long
Mach Number Range: 0 to 0.2
Fan Drive Rigs: 1000, 2000, and 5000 shp
1024 channel pressure measurement system
Flow Visualization
Pressure sensitive paint
Both conventional and focused Schlerien systems
Sheet laser
Oil flow visualization
High speed video - up to 1000 full screen frames/s
Remote Access Control Room
Real-time remote access to all data
Online calibration
Video conferencing in real time
Workstations supplied for remote site
Secure network connections provided
WIND TUNNEL APPLICATION IN RACING AERODYNAMICS
Design Objectives
Increase Down force.
Reduce Drag.
Development Tools
On-Road Testing.
Full Scale Wind Tunnel.
Scale Model Wind Tunnel.
Computational Fluid Dynamics.
Full Scale Wind Tunnel
Pros:
Controlled environment
Minimal setup time
Minimal setup cost
High test speed (up to 200 mph)
Good for radiator flow work
Flow visualization
Cons
Expensive facility costs (approx. $1800/hr)
Expensive to produce test parts
Limited application for ground effects cars
Scale Model Wind Tunnel
Pros:
Controlled environment
Good ground effect simulation
Quick ride height mapping
Flow visualization
Less expensive test parts production
Cons
Expensive facility costs (approx. $1100/hr)
High initial costs (vehicle scan, model production)
Long lead-time for initial test
Reynolds's number effects