scholarly journals Transient Thermal Response of Turbulent Compressible Boundary Layers

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Hongwei Li ◽  
M. Razi Nalim ◽  
Charles L. Merkle
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Laminar Flow ◽  
Thermal Boundary Layer ◽  
Thermal Response ◽  
Thermal Conditions ◽  
Steady State Solution ◽  
Similarity Transformations ◽  
Keller Box Method ◽  
Transient Thermal

A numerical method is developed with the capability to predict transient thermal boundary layer response under various flow and thermal conditions. The transient thermal boundary layer variation due to a moving compressible turbulent fluid of varying temperature was numerically studied on a two-dimensional semi-infinite flat plate. The compressible Reynolds-averaged boundary layer equations are transformed into incompressible form through the Dorodnitsyn–Howarth transformation and then solved with similarity transformations. Turbulence is modeled using a two-layer eddy viscosity model developed by Cebeci and Smith, and the turbulent Prandtl number formulation originally developed by Kays and Crawford. The governing differential equations are discretized with the Keller-box method. The numerical accuracy is validated through grid-independence studies and comparison with the steady state solution. In turbulent flow as in laminar, the transient heat transfer rates are very different from that obtained from quasi-steady analysis. It is found that the time scale for response of the turbulent boundary layer to far-field temperature changes is 40% less than for laminar flow, and the turbulent local Nusselt number is approximately 4 times that of laminar flow at the final steady state.

scholarly journals Transient Thermal Response of Turbulent Compressible Boundary Layers

2008 ◽  
Author(s):  
Hongwei Li ◽  
M. Razi Nalim ◽  
Charles L. Merkle
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Thermal Boundary Layer ◽  
Thermal Conditions ◽  
Steady State Solution ◽  
Transient Heat Transfer ◽  
Transfer Coefficients ◽  
Transient Time ◽  
Transient Thermal

A general numerical method is developed with the capability to predict the transient thermal boundary layer response under various flow and thermal conditions. The transient thermal boundary layer variation due to a moving compressible turbulent fluid of varying temperature was numerically studied on a 2-D semi-infinite flat plate. The Reynolds-averaged boundary-layer equations are solved based on the compressible Falkner-Skan transformation. Turbulence is modeled using a two-layer eddy-viscosity model developed by Cebeci and Smith, and the turbulent Prandtl number formulation originally developed by Kays and Crawford. The governing differential equations are discretized with the Keller-box method. The numerical accuracy is validated through grid independence studies and comparison with the steady state solution. In turbulent flow as in laminar, heat transfer coefficient is initially very different from that obtained from quasi-steady analysis. It is found that, both the transient time scale and the magnitude of the transient heat transfer coefficients differ significantly between turbulent and laminar flow. The more complex variation of transient heat transfer rate in turbulent flow is evident, and needs further study.

An airfoil theory of bifurcating laminar separation from thin obstacles

1990 ◽  
Vol 216 ◽  
pp. 255-284 ◽  
Author(s):  
C. J. Lee ◽  
H. K. Cheng
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Steady State ◽  
Steady State Solution ◽  
Equation System ◽  
Branch Points ◽  
Laminar Separation ◽  
Kutta Condition ◽  
Numerical Studies ◽  
Steady State Solutions

Global interaction of the boundary layer separating from an obstacle with resulting open/closed wakes is studied for a thin airfoil in a steady flow. Replacing the Kutta condition of the classical theory is the breakaway criterion of the laminar triple-deck interaction (Sychev 1972; Smith 1977), which, together with the assumption of a uniform wake/eddy pressure, leads to a nonlinear equation system for the breakaway location and wake shape. The solutions depend on a Reynolds numberReand an airfoil thickness ratio or incidence τ and, in the domain$Re^{\frac{1}{16}}\tau = O(1)$considered, the separation locations are found to be far removed from the classical Brillouin–Villat point for the breakaway from a smooth shape. Bifurcations of the steady-state solution are found among examples of symmetrical and asymmetrical flows, allowing open and closed wakes, as well as symmetry breaking in an otherwise symmetrical flow. Accordingly, the influence of thickness and incidence, as well as Reynolds number is critical in the vicinity of branch points and cut-off points where steady-state solutions can/must change branches/types. The study suggests a correspondence of this bifurcation feature with the lift hysteresis and other aerodynamic anomalies observed from wind-tunnel and numerical studies in subcritical and high-subcriticalReflows.

Microflow Heat Transfer Effectiveness: Questioning the “Area/Volume-Argument”

2011 ◽  
Author(s):  
Heinz Herwig
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Steady State ◽  
Thermal Boundary Layer ◽  
Heat Transfer Performance ◽  
Characteristic Length ◽  
Transfer Performance ◽  
Layer Behavior ◽  
Steady State Heat ◽  
Steady State Heat Transfer

The often used argument that heat transfer in micro-sized devices is superior due to the fact that the transfer area scales like L2 but the volume like L3 with L as a characteristic length is critically analyzed for various heat transfer situations. It turns out that for steady state heat transfer cases the thermal boundary layer behavior is more important. In general, dimensional analysis should be applied to understand how the heat transfer performance changes when scales are reduced from macro- to micro-size.

Heat Transfer in the Laminar Boundary Layer Over an Impulsively Started Flat Plate

1975 ◽  
Vol 97 (3) ◽  
pp. 482-484 ◽  
Author(s):  
C. B. Watkins
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Laminar Flow ◽  
Flat Plate ◽  
Constant Temperature ◽  
Laminar Boundary Layer ◽  
Temperature Difference ◽  
Thermal Boundary Layer ◽  
Numerical Solutions ◽  
Prandtl Numbers

Numerical solutions are described for the unsteady thermal boundary layer in incompressible laminar flow over a semi-infinite flat plate set impulsively into motion, with the simultaneous imposition of a constant temperature difference between the plate and the fluid. Results are presented for several Prandtl numbers.

Thermal Simulation Benchmark of Graphic Module Under Installed, Operating Conditions

2005 ◽  
Author(s):  
Fariborz Forghan ◽  
Gregory J. Kowalski ◽  
Mansour Zenouzi ◽  
Hameed Metghalchi
Keyword(s):  
Steady State ◽  
Computer Games ◽  
Electronic Device ◽  
Thermal Response ◽  
Thermal Simulation ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Software Environment ◽  
Transient Thermal ◽  
Graphic Module

The thermal performance of a graphic module on graphic card is theoretically and experimentally investigated. Unlike prior benchmark studies, this study involves a practical electronic device operating in a real software environment. The temperatures at five locations on the module and at one point on the board are measured as a function of time during the operation of a series of computer games. The theoretical model is developed using Flotherm to simulate the transient thermal response. There is close agreement from 3% to 10% between the numerical steady state case prediction and test data. The calculated transient trends using Flotherm model closely agree with experimental results and demonstrate the rapid increase in temperature as the number of module operations increases during the games. The results for the maximum temperature are directly linked to the software operation and exhibit a superposition type behavior in which the observed maximum operating temperature can exceed that estimated by steady state conditions. As expected, the results demonstrate that a carefully constructed thermal simulation can accurately predict the thermal response of a module under actual operating conditions.

A Numerical Study of the Laminar Flow of Non-Newtonian Fluids Along a Vertical Wall

1973 ◽  
Vol 40 (1) ◽  
pp. 290-292 ◽  
Author(s):  
T. M. T. Yang ◽  
D. W. Yarbrough
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Laminar Flow ◽  
Power Law ◽  
Analytical Solutions ◽  
Numerical Study ◽  
Vertical Wall ◽  
Newtonian Fluids ◽  
Momentum Integral ◽  
Accelerating Flow

The momentum integral technique is used to describe the steady-state, laminar, accelerating flow of a power-law liquid film along a vertical wall. Values for film thicknesses and boundary-layer thicknesses are obtained numerically and compared with existing analytical solutions for Newtonian fluids.

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