On the Flow Effects of a Small Device

摘要

An experimental and computational investigation of the interaction mechanismsbetween a single vortex generator (VG) and boundary layer (BL) flow is conducted. Theobjectives are to study the resulting flow-field characteristics and to validate acomputational model. The collected data may be analyzed to obtain simplified modelsfor use in the design case. An important parameter of the investigation is the relativeheights of the VG and the BL, with emphasis on the small device case.The investigated VG is a delta 60°, immersed in a turbulent BL. The ratio between theVG height and the BL thickness is 1/3. The experimental environment is obtained in awind-tunnel of long walls and low speed, where a VG is attached to the ceiling, inclined20°to the main flow. The procedure includes yaw meter measurements in the VG wakeand visualization of the limiting wall flow. CFD simulations performed by a Fluent 6.3numerical code are compared with the experimental findings to validate the theoreticalmodels and to gain more insight into the complex flow interaction.It is found that the VG has a large influence on the BL, despite its small relativedimensions. A wide mixing zone develops inside the BL and a correspondingenhancement of the BL momentum near the wall is obtained. A feeding layer is formedbetween the wall and the vortex, in addition to the known feeding sheet over the leadingedge. A shallow separation region of recirculation is found around the apex and down-streamat the pressure side. A complex wake structure is observed, including arelatively strong side-wash and high shear regions. A good agreement is obtainedbetween the computed results and the experimental data, but the computed diffusion atthe VG down-stream wake is greater than the experimental diffusion. This finding maybe explained by an insufficient density of the numerical grid at the wake region.