Some studies on transport phenomena in presence of a bluff body

Abstract

Transport phenomena around bluff bodies have been a subject of considerable research interest. Heat transfer characteristics inside a channel in presence of bluff body and effect of turbulence level on transport process around bluff bodies encompassing laminar and turbulent regime covering a Reynolds number range of 10-2,00,000 along with turbulence intensities varying from 5% to 40% are studied in this work. Here bluff bodies of five different shapes are considered, namely a) Circular cylinder, b) Square cylinder, c) Equilateral triangular prism, d) Diamond and e) Trapezium shape bluff bodies. The effect of turbulence intensity on the transport phenomena over two-dimensional bluff bodies is investigated. The governing equations of continuity, momentum, and energy equations are solved along with transition SST Model for the closure of turbulence. The simulation results are validated with experimental correlations that show good agreements. This work demonstrates that the transition SST Model can effortlessly bridge all flow regimes for predicting the heat transfer. The study quantifies the effect of inlet turbulence intensity on enhancing heat transfer from the bluff bodies. The drag and pressure coefficients are found to be unaffected by inlet turbulent intensity. An operative study of different bluff bodies is incorporated in this work. The bluff bodies are taken triangular prism, diamond and trapezoidal shaped bodies with the identical hydraulic diameter D, which is further the non-spatial length scale. The flowing medium i.e., the air is considered to have a constant Prandtl number (0.71). This work explains that transition SST Model can effortlessly link all flow regimes for predicting the heat transfer. The study quantifies the effect of inlet turbulence intensity on improving heat transfer from different bluff bodies. As part of the present work, an attempt has been made to study the augmentation of heat transfer on a channel wall in the presence of the bluff body of different shapes. Heat transfer enhancement in a channel in presence of bluff bodies of different shape has been numerically investigated in the turbulent flow regime with Reynolds number ranging from 100-2,00,000. The hydraulic diameter of the bluff body (Three different shapes namely Triangular Prism (TP), Diamond and Trapezoidal considers in this work) is taken as characteristic length. The inlet turbulent intensities are varied from 5% to 40%. The aspect ratio between channel to the bluff body is fixed at 4. The velocities and pressures were predicted using a semi-implicit pressure linked equations (SIMPLE) scheme. The results show that in the presence of triangular prism, heat transfer in a channel is augmented by around 10%. The presence of TP enhances heat transfer all through the downstream region. The analysis shows that the amount of enhancement increases with inlet turbulent intensity. The study quantifies the effect of inlet turbulence intensity on enhancing heat transfer from all other bluff bodies. Augmentation is associated with higher values of the skin friction coefficient on the channel wall. The Augmentation is also expressed as a percentage increased of heat transfer from a similar system without the diamond bluff body. For trapezoidal bluff body different configurations as (a) large edge of trapezium facing the flow (b) small edge facing flow and (c) trapezium is symmetrically placed is considered. Results show that the small edge facing upstream show better heat transfer performance. The thermohydraulic efficiency for three bluff bodies is also computed.