THE INFLUENCE OF WIND TUNNEL AIRFLOW STRAIGHTENING HONEYCOMBS ON AIRFLOW UNIFORMITY

Abstract

Airflow turbulence in wind tunnels are one of the biggest problems that distort and produce inaccurate test results. In order to reduce airflow turbulence it is appropriate to use airflow straightening honeycombs. They straighten the airflow so that it is parallel to the longitudinal axis of the tunnel. The aim is to reduce the turbulence in the cross-sectional area of the tunnel.

The research was carried out on a laboratory bench (15 m long, 2 m wide and 1 m high wind tunnel), in the Agricultural Engineering and Safety Department of the Vytautas Magnus University. Air velocity measurements in the wind tunnel were carried out in 4 different cross-sections, I, II, III and IV, at distances of 5 m, 7 m, 9 m and 11 m respectively from the axial-fans. The influence of the airflow straightening honeycombs on the uniformity of the airflow velocity distribution over the cross-sectional area was investigated by blowing the airflow and varying the airflow velocity in the test section of the tunnel (11 m away from the fans) between 2 m∙s^-1 and 12 m∙s^-1. Two easily removable airflow straightening honeycombs are installed at the front and rear of the wind tunnel, 1 m and 14 m downstream of the fans. The honeycombs are hexagonal tubes of 33 mm high, 40 mm wide and 400 mm long. The flow straightening honeycombs have been shown to provide a constant airflow over the length of the tunnel at air velocities between 10 m∙s^-1 and 12 m∙s^-1. The numerical values of the air velocity at 11 m from the fans are then about 10 % higher. As the velocity of the blowing air in the wind tunnel is increased from 2 m∙s^-1 to 12 m∙s^-1 by the two axial fans, the turbulence gradually decreases. It has been found that airflow straightening honeycombs reduce turbulence by 25–30 % only at airflow speeds between 6 m∙s^-1 and 12 m∙s^-1. At air velocities of 4 m∙s^-1 turbulence remains significantly unaffected.