Comparison on flow field characteristics of four wind tunnel contraction sections

Based on the high subsonic linear cascade wind tunnel of Northwestern Polytechnical University, the outlet flow field of Witozinsky contraction section was measured, and the poor directional field quality was found. Besides, the core area was reduced by 15% at pitchwise compared with the velocity and total pressure fields. Then exit core area, uniformity and separation characteristics of four contraction sections were compared by simulation. It was found that Witozinsky curve contracted at front, and contracting too fast caused vortex at inlet, but the outlet uniformity was better due to the longer outlet steady flow section. In contrast, double cubic curve mainly contracted at rear with greater forward pressure gradient of mainstream, so there existed thinner boundary layer, smaller deviation angle and better separation characteristics. The existing three-dimensional structure of Witozinsky contraction section widens the core area while disturbing airflow, deteriorating the velocity and direction fields, and increasing the deviation angle up to 43%. The inlet pipe diameter has little effect on the flow field characteristics of the double cubic contractions.