Investigation of Flow in a Low-Speed Wind Tunnel (Research Paper Sample)

Investigation of flow in a low-Speed wind tunnel
Name:
Instructor:
Institution:
Course:
Introduction
Wind tunnels are machines used to simulate air movement around an aircraft flight. Aeronautical Engineers control the conditions in the wind tunnel that affect the motion and force of the aircraft (Noda 2012). The engineers can determine the extent of force on real, full-size aircraft by making accurate measurement. The engineers connect the sub-scale model of arrangement to be tested in working section of the wind tunnel.
A fan, in current low –speed wind tunnel draws air into the entrance of wind tunnel. Accelerated air passes through Contraction that has the screen mounted to allow smooth flow of air before entering the working section. The air decelerates in the diffuser after passing the over the model, before leaving the wind tunnel. Main difficulties in using the wind-tunnel are to extrapolate the measurement made to the actual flight conditions (MITSUHASHI 2006).The aim of this experiment is to;Gain experience in use of low-speed and its accompanying instrumentation for aerodynamics measurements.Measure the static pressure distribution along the length of wind-tunnel and to match the results of the prediction using one-dimensional, inviscid- flow theory.Measure the stagnating-pressure distribution in the region to the lower wall of the working section, whose data is used to determine the velocity profile normal to the wind-tunnel wall, indicating the extent of flow influenced by air viscosity.
Background
There is the great diversity of wind tunnel that are designed for different purpose and speed range. The model to be tested is commonly placed in the test section of the wind tunnel. The design of the tunnel determines the rate (Buckingham 2009). The speed range choice influence the tunnel design due to compressibility effect.For subsonic flows, air density is constant, and an increase in the cross-sectional area causes the flow velocity to decrease and increase pressure and vice visa. In this flow, the test section is placed in the Contraction section and upstream of the diffuser.
Fig 1. Subsonic tunnel design.
For supersonic flow, there is change in air density because of compressibility, an increase in cross-sectional area causes the flow to increase in velocity and decrease in pressure.
Fig 2. Supersonic tunnel design.
In both of above design, the pressure is decreased and velocity is increased comparative to the station upstream of the test section (Buckingham 2009).
The air inside the tunnel is made to circulate by the fan on the other side of the tunnel. The air move continuously through the wind tunnel, passing over the mode placed in the test section.
Fig 3. Wind tunnel
Manometer fluid height (h) is a measure of static pressure along the tunnel wall, relative to atmospheric pressure. The static pressure at station 1 is given as;
P1g=ρmanometergh1sinθ=S.G Pwatergh1sinθ
Where ρmanometer and S.G are density and specific gravity of the manometer fluid, θ is the inclination angle of multi-tube manometer.
Taking static pressure at station 9 as reference to working section, non- dimensional pressure coefficient (Cp) is defined as;
Cp1=p1g-P9gP09g-P9g=h9-h1h9-h23
Where P09gis stagnation pressure at station 9. The static-pressure at station 2 to 21A are determined in the same way.
Mass-flow rate of air at all station is given as;
m=pAU
Where A and U are cross-sectional area and air velocity at the given station.
When Bernoulli’s equation is applied between reference station 9 and given station;
P+12PU2-P9+12U92=P09
The static-pressure coefficient is;Cp=P-P9P09-P9=1/2ρ(U92-U2)1/2ρU92=1-UU92=1-mPAmPA92 Cp=1-A9A2
Free stream velocity(Ue) in working section is calculated as;
Ue=2(P0e-P)ρ=2 S.G.ρwaterg(h9-h23e)sinθρair
The air mass flow rate through the wind tunnel is determined in reference to station 9;
M=ρairA9Ue
Apparatus
In both of above design, the pressure is decreased, and velocity is increased comparative to the station upstream of the test section.Low-speed, open-return wind tunnel, wall static pressure tapping are provided along the tunnel length that are connected to inclined multi-tube manometer.A reference pilot-static probe is located at the center of working section and connected to Betz-type water manometer.Barometer and thermometer provided measures ambient atmospheric pressure and temperatures.
Procedures
The wind tunnel was switched on for the flow conditions to stabilize.The fluid height of multi-tube manometer, wind tunnel cross-sectional area in different, specific gravity of the manometer fluid and angle of inclination of manometer were recorded.Small pitot probe was traversed from working section wall while recording stagnation pressure at intervals.Betz manometer reading, laboratory ambient pressure and ambient temperature were recorded.Wind tunnel was switched off.
Data analysis
Table 1:Atmospheric condition in the room.
The density in above table was calculated using equation of state of a perfect gas
Table 2: Manometer Details.
The velocity in working section was calculated using Bernoulli’s equation. Which uses the following equation as illustrated earlier:
Ue=2(P0e-P)ρ=2 S.G.ρwaterg(h9-h23e)sinθρair
Table 3: Reference condition in working section
Dynamic pressure was calculated using static pressure at station 9 as reference static pressure.
Velocity calculated using Bernoulli’s equation.
Mass flow rate calculated using continuity equation.
Table 4: Static pressure distribution along wind tunnel
Table 5: Boundary layer traverse
<...