Influence of the Length of an Inclined Groove on the Turbulent Heat Transfer Enhancement on a Plate with a Surface Vortex Generator during Air Flow

Enhancement of heat transfer during separated flow around a groove having hemispherical ends, inclined at an angle of 45° to the direction of the air flow, and placed on the isothermal section of a heated plate is studied experimentally and numerically. The influence of the trench insert length on heat transfer and flow is studied. A one-and-a-half-fold increase in the relative heat transfer coefficient at the bottom of a “long” oval-trench dimple (OTD) has been revealed as compared to a smooth plate. It has been established that inclined oval dimples with a trench insert length taken relative to its width L = 0.05–1 and inclined OTDs with L greater than 2 differ radically in the structure of the vortex flow. In an inclined OTD with L = 5, a one-and-a-half-fold increase in the maximum return flow velocity and a threefold increase in the maximum swirling flow velocity as compared to similar parameters in a spherical dimple are observed. The relative heat transfer coefficient on the surface of the inclined groove is maximum at L = 2.5 and considerably exceeds the average relative coefficient of heat transfer from the heated section of the plate with the OTD. It is shown that acceleration of the near-wall flow over the inlet part of the inclined OTD under conditions of anomalous heat transfer enhancement is associated with an increase in the longitudinal component of the velocity at the cut of the “long” OTD to almost 60% of the velocity of the oncoming flow, as well as with thinning of the thermal boundary layer.