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22.10.2012 20:43:55
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7.2. Determination of air velocity.

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In determining the velocity of the air in the chamber aerodynamic stand the main parameters measured, in accordance with the Bernoulli equation for an incompressible fluid and the continuity equation, is the difference between the static pressure in different sections of the wind tunnel. The pressure of the air flow in different sections of the aerodynamic stand ADS-2 is determined by the water pressure gauges, which are glass tubes filled to a certain level of distilled water. Scheme for determining static pressure drop in vertical cross-sections of the working chamber aerodynamic stand ADS-2 is shown in Fig. 8.

Along the perimeter of the working chamber 1 of a wind tunnel ADS-2 in three sections the height of the working chamber located static pressure sensors, which are 1.0 mm diameter holes. in the walls of the working chamber 1 with nipples 2, located on the outer side of the working chamber. In addition, the static pressure sensors located in sections of the wind tunnel ADS-2 in front of the working chamber 1, with the working chamber 1 and 3 in the settling chamber. Each measured section housed three static pressure sensor.

To ensure that the average static pressure readings and avoid accidental errors in these sections of the working chamber 1 of a wind tunnel ADS-2 nozzle 2 sensors static pressure measured in each section of the tube 4 is connected to a collector 5, which is a tube 6 is connected to a glass tube manometer 7 water manometer. Water pressure gauge (in Fig. Not shown) is a shield, which are glass manometer tube 7 and 8 expansion tank filled with liquid (distilled water tinted). One end of the manometer tube 7 is connected with hose two static pressure sensor, the other end of manometer tube 7 is connected to the expansion tank 8 rubber tubing 9. At the top of the tank lid 8 has an opening with a fitting 10, connected through a rubber tube and collector 5 with static pressure sensor section 0-0 prechamber 3. Each manometric tube 7 is provided with a measuring scale, so any change in velocity in the working chamber 1 immediately characterized by changes in static pressure drop in the test sections.

Under the action of the air flow having a different speed, and, consequently, different pressure on sections of the wind tunnel, the water level in the glass tubes of water gauge is changed. Fixing the difference in water levels during the experiment, we find the difference between the static pressures in these sections of the working chamber of a wind installation ADA-2. It uses the well-known relation:

1 = 9.81 Pa                                                                                                          (2).

The flow rate adjustment of the working chamber was determined by differential pressure using the Bernoulli equation for incompressible fluids:

P = psto + 1/2q Vo*Vo = pst1 + 1/2q V1*V1                                                                   (3)

The continuity equation:

qFoVo = qF1V1                                                                                                                   (4)

P - total pressure, Pa;
psto, pst1 - static pressure in sections 0-0 and 1-1, respectively, Pa;
Vo, V1 - the rate in sections 0-0 and 1-1, respectively, m, s;
q - density of air, kg / m;
Fo, F1 - the area under consideration sections, m.

Then the air flow rate in section 1.1 of the working chamber, the unfilled researched work items that can be written as follows:

V1 =  , M / s                                                               (5)

Given that the cross-sectional area under study work items placed in the chamber is much smaller than the cross sectional area of ​​the working chamber of the calculations can be neglected. Thus, the cross-sectional area of ​​the working chamber placed in the work items and work item is without about the same.

Then the air velocity in the i-th section of the working chamber filled with work items, will be:

Vi =  [ = = = M / s]         (6)

psto, psti - static pressure in sections 0-0 and ii, respectively, Pa;
Fo, Fi - the area under consideration sections m2.

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