Experimental Investigation on the Impact of Wall Heating on Mixed Convection Turbulent Boundary Layer Flow Structure
Abstract
The hydrodynamic and thermal boundary layers are known to be key regulators of the interfacial transport of mass, momentum and heat, which are crucial in a wide range of engineering and environmental applications. The boundary layers encountered in these applications are often turbulent in nature and characterized by the presence of three-dimensional motion and non-linear dissipative phenomena. The presence of heat transfer between the bulk fluid and the solid wall increases flow complexity due to the interaction of the buoyant force with flow inertia and non-linear coupling between thermo-fluid variables. As a key contributor to multiple engineering systems and environmental phenomena, advancement of the current knowledge on turbulent boundary layer dynamical behaviors is crucial.
In the present study, turbulent boundary layer flow over a heated horizontal smooth wall was investigated utilizing an experimental approach. The current state-of-the-art techniques for 3D flow characterization are often limited in their broad applicability. The present knowledge is improved upon with the development of a novel technique based on volumetric illumination with a multi-color pattern. In the absence of heat transfer, the turbulent boundary layer is known to contain a wide range of dynamical phenomena whose behaviors still lack a comprehensive understanding. The present study investigated the unheated turbulent boundary layer utilizing a unique implementation of the Particle Image Velocimetry (PIV) technique to characterize the three-dimensional (3D) nature of the flow and reported new findings on near-wall turbulent flow behavior. In the presence of heat transfer, once the buoyant force magnitude is sufficiently large, thermals detach and rise from the heated wall. The characteristics of thermals in a heated turbulent boundary layer was investigated in 3D utilizing PIV. A novel image processing algorithm was developed to detect thermals. The modification to the turbulent boundary layer velocity field by wall heating was studied utilizing PIV data. Results indicate that boundary layer behavior is influenced by the buoyant force via modification to the turbulent velocity field and associated velocity statistics. This study provides multiple new contributions on flow characterization techniques and the behaviors of the turbulent boundary layer in the presence and absence of heat transfer.