Enhancement of Separation Flow and Heat Transfer in a Boomerang-Type Groove on the Channel Wall

Abstract

The self-organization of a tornado-like vortex enhanced by the formation of an extraordinary transverse pressure drop and the onset of a negative pressure pole in the tornado core is observed in the case of a 45° deviation of the inlet section of streamwise oriented groove on the heated wall of plane-parallel channel with increase in the relative length of the section ξ, starting from 0.15. Tornado generation leads to the development of abnormal separation flow and heat transfer enhancement in the inlet inclined part of the groove. It is known that in the inclined rectilinear grooves the abnormal enhancement of separation flow and heat transfer is characterized by weakening of vortex structures and suppression of heat transfer in the end part of the groove. It is found that at the optimum relative length ξ the orientation of the end section of the groove along the flow in the channel leads to the penetration of intense swirling flow into the end zone of the boomerang-type groove and enhances heat transfer here. The optimal length of the inlet section ξ = 0.35 is determined. At this length, a 29% increase in the maximum heat transfer from the inner groove surface compared to the plane channel wall is achieved. In this case, the heat removal inside the boomerang-type groove is 1.2 times higher than that for the straight groove at the 45° inclination angle. The critical length of the inlet section (ξ = 0.7) starting from which the swirling flow leaves the groove without reaching its end is found. The critical length is characterized by the minimum relative hydraulic losses for the section bounded by the contour of the groove spot.