Numerical Investigation of Laminar Impinging Jet Cooling of a Protruded Heat Source

2021 ◽  
Author(s):  
Abhisek Ganguly ◽  
Shantanu Pramanik ◽  
Orkodip Mookherjee ◽  
Sayantan Sengupta
Keyword(s):  
Heat Flux ◽  
Wall Jet ◽  
Step Flow ◽  
Laminar Jet ◽  
Nusselt Numbers ◽  
Jet Cooling ◽  
Flow Prediction ◽  
Self Similar ◽  
Prandtl Numbers ◽  
And Diffusion

Abstract Thermofluid dynamics of an unconfined steady two-dimensional laminar jet impinging on an isothermal protruded heater is numerically studied for low jet inlet Reynolds number (Re) between 50 and 250. Results are shown for a range of impingement distance h/W between 1 to 10 for Prandtl numbers (Pr) 0.71 and 7.56. The volumetric entrainment increases with increasing h/W and decreasing Re. The reattachment distance of the wall jet appears to increase with Re and shows discernible deviation from the backward-facing step flow prediction for Re>150. Correlations are presented for average heater surface and sidewall Nusselt numbers as functions of Re and h/W for Pr=0.71 and Pr=7.56. In an overall convection dominant heat transfer, a relatively warmer and diffusion-dominated recirculation zone is identified adjacent to the sidewall with a low Nusselt number, which enhances significantly at Pr=7.56 when Re is increased beyond 100. At a low impingement distance, integrated kinetic energy flux shows greater magnitude in the impingement region but with a higher decay rate. The integrated heat flux is greatly influenced by Re, and the effect is more pronounced at Pr=0.71. Self-similar behavior is observed for the velocity and heat flux profiles throughout the length in the developed region and for the temperature distribution over the heater. Both high Re and high h/W seem to adversely affect the self-similar behavior owing to a slower wall jet development.

scholarly journals Adjoint shape optimization of a duct for a wall jet film cooling setup

2021 ◽  
Vol 2119 (1) ◽  
pp. 012018
Author(s):  
N N Kozyulin ◽  
M S Bobrov ◽  
M Y Hrebtov
Keyword(s):  
Heat Flux ◽  
Shape Optimization ◽  
Film Cooling ◽  
Cooling System ◽  
Velocity Ratio ◽  
Optimization Method ◽  
Wall Jet ◽  
Mean Velocity ◽  
Jet Cooling ◽  
The Mean

Abstract The paper presents the results of optimization of the geometric parameters of the simplified wall jet cooling system using a modified Adjoint Shape optimization method for algebraic systems of equations (Discrete Adjoint Optimization). The modification consists in using a linearized discrete system of equations with the replacement of derivatives by their finite-volume approximations. The jet flowed through a duct and out from a nozzle. The duct was inclined at an angle of 35 degrees to the cooled wall. The mean velocity ratio between the jet and the main flow was set to 2. The total heat flux on the cooled wall was taken as a cost function. The problem was considered in a two-dimensional stationary turbulent formulation (RANS). As a result of optimization, the shape of the duct changed significantly, affecting the flow inside it. The optimization led to the disappearance of the recirculation zone and reattaching of the jet to the cooled wall. As a result of the optimization performed, the heat flux at the wall increased by 20%.

The Skin Friction and Heat Transfer in a Laminar Plane Wall Jet That Evolves From a Uniform Velocity to Its Self-Similar Behavior

2005 ◽  
Author(s):  
Johnny Issa ◽  
Alfonso Ortega
Keyword(s):  
Reynolds Number ◽  
Prandtl Number ◽  
Skin Friction ◽  
Skin Friction Coefficient ◽  
Wall Jet ◽  
Local Skin ◽  
Uniform Velocity ◽  
Nusselt Numbers ◽  
Self Similar ◽  
Finite Volume Approach

The plane, steady, laminar wall jet with a uniform velocity and temperature profiles at the jet exit is numerically investigated using a two-dimensional finite volume approach for a variety of Reynolds numbers and Prandtl number of 0.712 and 7. Between the jet exit and the downstream self-similar behavior, the flow exhibits a developing region that is not self-similar. The location of the dimensionless virtual origin is carefully investigated and expressed as a function of Reynolds number. The local skin friction coefficient is observed to converge to the analytical self-similar solution at downstream locations. Since no analytical solution exists for the temperature field in either the developing or self-similar regions of this problem, the thermal solution is investigated for both isothermal and isoflux boundary conditions at the wall. The local and overall skin friction coefficients, in addition to the local and overall Nusselt numbers, are reported as a function of Reynolds number, Prandtl number and the dimensionless location downstream of the jet exit.

Fluid Mechanics and Heat Transfer Measurements in Transitional Boundary Layers Conditionally Sampled on Intermittency

1994 ◽  
Vol 116 (3) ◽  
pp. 405-416 ◽  
Author(s):  
J. Kim ◽  
T. W. Simon ◽  
M. Kestoras
Keyword(s):  
Heat Flux ◽  
Plate Boundary ◽  
Turbulent Heat Flux ◽  
Transitional Flow ◽  
Turbulent Heat ◽  
Mean Velocity ◽  
Power Spectral ◽  
Turbulent Characteristics ◽  
Transition Models ◽  
Prandtl Numbers

An experimental investigation of transition on a flat-plate boundary layer was performed. Mean and turbulence quantities, including turbulent heat flux, were sampled according to the intermittency function. Such sampling allows segregation of the signal into two types of behavior—laminarlike and turbulentlike. Results show that during transition these two types of behavior cannot be thought of as separate Blasius and fully turbulent profiles, respectively. Thus, simple transition models in which the desired quantity is assumed to be an average, weighted on intermittency, of the laminar and fully turbulent values may not be entirely successful. Deviation of the flow identified as laminarlike from theoretical laminar behavior is due to a slow recovery after the passage of a turbulent spot, while deviation of the flow identified as turbulentlike from fully turbulent characteristics is possibly due to an incomplete establishment of the fully turbulent power spectral distribution. Measurements were taken for two levels of free-stream disturbance—0.32 and 1.79 percent. Turbulent Prandtl numbers for the transitional flow, computed from measured shear stress, turbulent heat flux, and mean velocity and temperature profiles, were less than unity.

scholarly journals Heat flux and diffusion velocities behind shock wave: state-to-state approach

2017 ◽  
Author(s):  
O. Kunova ◽  
E. Kustova ◽  
M. Mekhonoshina ◽  
E. Nagnibeda
Keyword(s):  
Shock Wave ◽  
Heat Flux ◽  
Wave State ◽  
And Diffusion

Stochastic dynamics and model reduction of amplifier flows: the backward facing step flow

2013 ◽  
Vol 719 ◽  
pp. 406-430 ◽  
Author(s):  
G. Dergham ◽  
D. Sipp ◽  
J.-Ch. Robinet
Keyword(s):  
Stochastic Dynamics ◽  
Empirical Orthogonal Functions ◽  
Backward Facing Step ◽  
Orthogonal Functions ◽  
Step Flow ◽  
Flow Response ◽  
Entire Flow ◽  
Random Flow ◽  
Value Decomposition ◽  
And Diffusion

AbstractMethods for investigating and approximating the linear dynamics of amplifier flows are examined in this paper. The procedures are derived for incompressible flow over a two-dimensional backward-facing step. First, the singular value decomposition of the resolvent is performed over a frequency range in order to identify the optimal and suboptimal harmonic forcing and responses of the flow. These forcing/responses are shown to be organized into two categories: the first accounting for the Orr and Kelvin–Helmholtz instabilities in the shear layer and the second for the advection and diffusion of perturbations in the free stream. Next, we investigate the dynamics of the flow when excited by a white in space and time noise. We compute the predominant patterns of the random flow which optimally account for the sustained variance, the empirical orthogonal functions (EOFs), as well as the predominant forcing structures which optimally contribute to the sustained variance, the stochastic optimals (SOs). The leading EOFs and SOs are expressed as a linear combination of the suboptimal forcing and responses of the flow and are related to particular instability mechanisms and/or frequency intervals. Finally, we use the leading EOFs, SOs and balanced modes (obtained from balanced truncation) to build low-order models of the flow dynamics. These models are shown to accurately recover the time propagator and resolvent of the original dynamical system. In other words, such models capture the entire flow response from any forcing and may be used in the design of efficient closed-loop controllers for amplifier flows.

Numerical Investigation of Heat Transfer in Rectangular Microchannels Under H2 Boundary Condition During Developing and Fully Developed Laminar Flow

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
V. V. Dharaiya ◽  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Fluid Flow ◽  
Microfluidic Devices ◽  
Transport Processes ◽  
Uniform Heat Flux ◽  
Data Set ◽  
Nusselt Numbers ◽  
Aspect Ratios

Study of fluid flow characteristics at microscale is gaining importance with shrinking device sizes. Better understanding of fluid flow and heat transfer in microchannels will have important implications in electronic chip cooling, heat exchangers, MEMS, and microfluidic devices. Due to short lengths employed in microchannels, entrance header effects can be significant and need to be investigated. In this work, three dimensional model of microchannels, with aspect ratios (α = a/b) ranging from 0.1 to 10, are numerically simulated using CFD software tool fluent. Heat transfer effects in the entrance region of microchannel are presented by plotting average Nusselt number as a function of nondimensional axial length x*. The numerical simulations with both circumferential and axial uniform heat flux (H2) boundary conditions are validated for existing data set for four wall heat flux case. Large numerical data sets are generated in this work for rectangular cross-sectional microchannels with heating on three walls, two opposing walls, one wall, and two adjacent walls under H2 boundary condition. This information can provide better understanding and insight into the transport processes in the microchannels. Although the results are seen as relevant in microscale applications, they are applicable to any sized channels. Based on the numerical results obtained for the whole range, generalized correlations for Nusselt numbers as a function of channel aspect ratio are presented for all the cases. The predicted correlations for Nusselt numbers can be very useful resource for the design and optimization of microchannel heat sinks and other microfluidic devices.

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