The influence of wall heating on turbulent boundary layer characteristics during mixed convection

2021 ◽  
Vol 91 ◽  
pp. 108839
Author(s):  
Kadeem Dennis ◽  
Kamran Siddiqui
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Mixed Convection ◽  
Wall Heating

Investigation of Turbulent Flow Behavior in a Heated Boundary Layer

2019 ◽  
Author(s):  
Kadeem Dennis ◽  
Kamran Siddiqui
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Mixed Convection ◽  
Turbulent Flow ◽  
Flow Regime ◽  
Three Dimensional ◽  
Convection Flow ◽  
Buoyant Force ◽  
Layer Flow ◽  
Flow Inertia

Abstract The boundary layers are known to play key roles in many engineering systems. The hydrodynamic boundary layer found in these systems is often turbulent in nature and heat transfer is involved which further increases flow complexity due to the influence of buoyancy. One of the constituent layers of the turbulent boundary layer, the inner layer, has been established as home to key dynamical turbulent phenomena which can be influenced by the buoyant force. In the mixed convection flow regime, flow inertia and buoyant force are on the same order of magnitude. In this regime, buoyant thermals rising from the wall interact with the inertia-driven turbulent flow field resulting in highly complex three-dimensional flow dynamics. Past research studies conducted in this flow regime have been mostly computational in nature with little experimental work. The current knowledge on the impact of the relative contributions by the buoyant force and flow inertia on turbulent phenomena in the mixed convection flow regime is very limited. This study reports on an investigation into the turbulent flow phenomena present in mixed convection turbulent boundary layer flow over a heated smooth horizontal flat plate. Experiments were performed in a closed loop wind tunnel where the turbulent boundary layer was heated from below. The multi-plane particle image velocimetry (PIV) technique was used to capture two-dimensional velocity fields over two planes with respect to the flow direction. Experiments were conducted over a range of Richardson numbers (Ri) between 0.0 and 2.0 to control the relative contribution of the buoyant force with respect to flow inertia. The measured velocity fields are used to describe the influence of buoyancy on the three-dimensional turbulent boundary layer flow.

Characterization of Thermals in a Heated Turbulent Boundary Layer

2019 ◽  
Author(s):  
Kadeem Dennis ◽  
Kamran Siddiqui
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Mixed Convection ◽  
Boundary Layer Flow ◽  
Three Dimensional ◽  
Mean Flow ◽  
Buoyant Force ◽  
Viscous Shear ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

Abstract The hydrodynamic boundary layer encountered in many practical engineering systems is turbulent in nature and known to play a significant role in governing the induced friction drag and species transport. In turbulent boundary layer flows, heat transfer is often involved which increases flow complexity due to the influence of buoyancy. When the buoyant force is sufficiently large in magnitude, thermals carrying heated fluid are known to detach and rise from the wall. Literature review shows that in mixed convection, thermals have been primarily identified through qualitative flow visualizations and there is a scarcity of their quantitative assessment. Furthermore, the evolution of thermals in the boundary layer with respect to flow inertia and viscous shear is not well-understood. Hence, there is a need for a better understanding of the dynamics of thermals in mixed convection turbulent boundary layer flow. The objective of this study is to experimentally investigate the three-dimensional nature of thermals rising from a turbulent boundary layer flow over a heated smooth horizontal flat plate. Experiments were performed in a closed loop low-disturbance wind tunnel with a test section featuring a 1 m long heated bottom wall. The multi-plane particle image velocimetry (PIV) technique was used to capture images in multiple planes with respect to the turbulent boundary layer mean flow direction for three-dimensional characterization. The measurements were conducted at Richardson numbers (Ri) of 0.3, 1.0, and 2.0. Flow visualization images are used to describe the nature of thermals and the dynamical processes involved during their interaction with bulk boundary layer flow. An image processing algorithm to detect thermals is then detailed and applied to experimental images. The performance of the new algorithm is then assessed in its ability to detect thermals.

scholarly journals DNS Study of Effects of Suddenly-Vanishing Wall Heating in Turbulent Boundary Layer

2012 ◽  
Vol 7 (1) ◽  
pp. 313-321 ◽  
Author(s):  
Hirofumi HATTORI ◽  
Syohei YAMADA ◽  
Tomoya HOURA
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Wall Heating
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