Numerical Study of the Heat Transfer Characteristics of a Turbulent Jet Impinging on a Cylindrical Pedestal (original) (raw)
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2012
In this study the numerical simulation of three dimensional turbulent impinging round jets are conducted using the CFD method. The two jets one impinging on a simple flat plate and the other impinging on a circular pedestal heated and mounted on a flat plate are investigated. The flow fields and heat transfer characteristics of the two cases are compared at a Reynolds number of 23000 and nozzle to target distance of six times the diameter of the jet. The purpose of this paper is studying the effect of existence of the pedestal on rate of heat transfer. Turbulent fluctuations in the velocity field are modeled using the Reynolds Averaged Navier-Stokes (RANS) methodology. Turbulence is assumed to be isotropic. The buoyancy and radiation heat transfer effects are neglected and the flow is considered to be incompressible. The simulations are performed using various turbulence models such as the Realizable k , k RNG , k SST and f 2 . There is a good agreement between the c...
Numerical Simulation of Heat Transfer in an Axisymmetric Turbulent Jet Impinging on a Flat Plate
2007
A computational study of the impingement of a thermally turbulent jet on a solid plate, using k e model, is reported. The possibility of improving the heat transfer is carried out according to the characteristic parameters of the interaction jet-wall. The close zone solid wall required a particular treatment using an economic method known as "wall functions". The numerical resolution of the equations is carried out using the finite volume method. For a fixed nozzle–plate distance, the influence of the Reynolds number on the stagnation point heat transfer is investigated. Good agreement with experimental results is observed. The influence of the nozzle–plate distance on the stagnation point Nusselt number is also discussed.
Numerical investigation is performed to study the effects of the L/d of the nozzle and jet-to-plate spacing on the local heat transfer distribution to normally impinging submerged air jet on smooth and flat surface. (v2-f model) has been used to simulate the flow and heat transfer in circular unconfined impinging jet configurations. The model has been validated against available experimental data sets, Four different nozzles each with an equivalent diameter of 16 mm are used during this study and jet-to-plate spacing from 0.5 to 12 nozzle diameters. Length-to-diameter ratio (L/d) of 0.5, 1, 2, and 4 is chosen for each nozzle configuration. Results have been obtained for a range of jet Reynolds number of 30000 and jet-to-target distances. The effect of confinement on the local heat transfer behavior has been determined. The local heat transfer characteristics are estimated Local and average Nusselt number on the impinged surface are presented for all the nozzle configurations investigated. In contrast the flow characteristics in the nozzle strongly affects the heat transfer rate Keywords: CFD, Transition, v2-f model, Turbulence.
Analysis of heat transfer and flow characteristics in turbulent impinging jet
Nuclear Engineering and Design, 2011
Jet impingement technique is characterized by a high heat removal capability. As such it has been proposed as a cooling method for the helium cooled divertor, a high-heat flux component of the future fusion reactor called DEMO. Since power plant efficiency depends on the divertor's heat removal capability it has to meet certain demands, i.e. high-heat transfer and low pressure drop. In this paper local heat transfer and flow characteristics of an axis-symmetric impinging jet are analyzed numerically using the RANS approach and eddy viscosity type SST turbulence model. Turbulence models and heat transfer predictions are validated on the free jet impingement experiment (Baughn and Shimizu, 1989). Since the numerical results are affected by the turbulence model the influence of the turbulent production is investigated in particular. The validated numerical model is further applied to analyze the effect of the nozzle inlet shape on the heat removal capability and pressure drop in the confined impinging jet. Two different nozzle inlet parameters are tested; chamfer angle  and chamfer depth L ch. The numerical results are compared with the experimental data (Brignoni and Garimella, 2000).
Aerodynamic and heat transfer analysis of a impinging jet on a concave surface
International Journal of Thermal Sciences, 2017
Impinging jets are often used in applications requiring important localized cooling. For example, this technique is commonly used to reduce blade temperatures inside gas turbines. When the jet impacts the inner surface of the leading edge of a gas turbine blade, this geometrical configuration is similar to a jet impinging a concave surface inside a cavity. Previous studies have shown that for a certain range of geometrical and dynamic parameters, a jet injected in a cavity may sometime become unstable which is characterized by an oscillatory or flapping movement of the flow within the cavity. The objectives of this study are to investigate some features of this behaviour from velocity fields inside the cavity, pressure coefficients and Nusselt number distributions on the concave surface. This was accomplished using unsteady numerical simulations of a laminar flow at different Reynolds numbers for six different cavity configurations. Furthermore, PIV measurements were realized for some of the configurations in order to validate the numerical results. The results show that for four geometrical configurations, the flow entered in an oscillatory movement inside the cavity. This behaviour can be related to the difference in pressure between the output channels and the main vortex structure present inside the cavity. However, no clear link has been established between the frequency of the oscillatory flow and the geometrical parameters used.
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/fluid-flow-and-heat-transfer-analysis-of-turbulent-multiple-circular-jets-impinging-on-a-flat-plate https://www.ijert.org/research/fluid-flow-and-heat-transfer-analysis-of-turbulent-multiple-circular-jets-impinging-on-a-flat-plate-IJERTV1IS7431.pdf Computations and Experiment investigations on a Flat plate and reported with constant heat flux imposed on bottom surface and five circular jets impinges on a top surface .The five circular jets consists of a central jet surrounded by four neighboring perimeter jets .Lampblack flow visualization technique and computation using shear stress transformation (K-ω) turbulent model and employed to describe the complex interaction of the wall jets and the associated flow structure. It is observed that the flow topology is practical independent of Reynolds number with in the investigation range but is significantly attend with the spacing between jet orifice and target surface. Primary pressure peaks are observed at the stagnation point and the secondary peaks are noticed at the interaction points of wall jets. A strong correlation between nusselt number and the pressure distribution is noticed.
Turbulent heat transfer for impinging jet flowing inside a cylindrical hot cavity
Thermal Science, 2015
Convective heat transfer from an isothermal hot cylindrical cavity due to a turbulent round jet impingement is investigated numerically. Three-dimensional turbulent flow is considered in this work. The Reynolds stress second order turbulence model with wall standard treatment is used for the turbulence predictions the problem parameters are the jet exit Reynolds number, ranging from 2x10 4 to 10 5 and the normalized impinging distance to the cavity bottom and the jet exit L f , ranging from 4 to 35. The computed flow patterns and isotherms for various combinations of these parameters are analyzed in order to understand the effect of the cavity confinement on the heat transfer phenomena. The flow in the cavity is divided into three parts, the area of free jet, and the area of the jet interaction with the reverse flow and the semiquiescent flow in the region of the cavity bottom. The distribution of the local and mean Nusselt numbers along the cavity walls for above combinations of the flow parameters are detailed. Results are compared against to corresponding cases for impinging jet on a plate for the case of the bottom wall. The analysis reveals that the average Nusselt number increases considerably with the jet exit Reynolds number. Finally, it was found that the average Nusselt number at the stagnation point could be correlated by a relationship in the form f Nu f (L , Re) .
Heat transfer in a turbulent slot jet flow impinging on concave surfaces
International Communications in Heat and Mass Transfer, 2013
An experimental and numerical study is conducted to investigate turbulent slot jet impingement cooling characteristics on concave plates with varying surface curvature. Air is used as the impingement coolant. In the experimental work, a slot nozzle specially designed with a sixth degree polynomial in order to provide a uniform exit velocity profile was used. The experiments were carried out for the jet Reynolds numbers in the range of 3423 ≤ Re ≤ 9485, the dimensionless nozzle-to-surface distance range of 1 ≤ H/W ≤ 14 for dimensionless values of the curvature of impinging surfaces in the range of R/L = 0.5, 0.725, and 1.3 and a flat impingement surface. Constant heat flux was applied on the plates. Numerical computations were performed using the k-ε turbulence model with enhanced wall functions. For the ranges of the governing parameters studied, the stagnation, and local and average Nusselt numbers have been obtained both experimentally and numerically. The numerical results showed a reasonable agreement with the experimental data.
Study of heat transfer for a pair of rectangular jets impinging on an inclined surface
International Journal of Heat and Mass Transfer, 2003
Critical design parameters in jet impingement heat transfer like nozzle hydraulic diameter, jet angle and velocity, physical properties of the fluid, and nozzle-to-target plane spacing are the subject. This paper identifies the dominant fluid-thermal characteristics of a pair of rectangular air jets impinging on an inclined surface. Heat transfer modes and flow characteristics are studied with eight different Reynolds numbers ranging from 500 to 20 000. Local and average Nusselt numbers are evaluated with two different boundary conditions on three specified lines located on the inclined surface. The correlation between stagnation Nusselt number and Reynolds number is presented. Turbulent intensity and wall y þ distributions are compared on three lines parallel to the incline. The effect of jet impingement angle on local and average Nusselt number is also documented. Finally, a correlation between the average Nusselt number, nozzle exit Reynolds number and the jet angle is documented.
International Journal of Thermal Sciences, 2008
The flow field of confined circular and elliptic jets was studied experimentally with a Laser Doppler Anemometry (LDA) system. In addition, heat transfer characteristics were numerically investigated. Experiments were conducted with a circular jet and an elliptic jet of aspect ratio four, jet to target spacings of 2 and 6 jet diameters, and Reynolds number 10 000. The toroidal recirculation pattern was observed in the outflow region for both geometries at dimensionless jet to plate distance 2. Higher spreading rates in the minor axis direction of the elliptic jet have also been mapped. Along the target plate, different boundary layer profiles were obtained for circular and elliptic jets at H/d = 2, but profiles became similar when dimensionless jet to plate distance was increased to 6. Positions of maximum radial and axial velocities and turbulence intensities have been determined for both geometries. For the confined circular and elliptic jet geometries, analysis of flow field measurements and numerical heat transfer results showed that inner peaks in local heat transfer closely relate to turbulence intensities in the jet and radial flow acceleration along the wall. Differences between the circular and elliptic jet, in terms of flow field and heat transfer characteristics, reduced with increase in the jet to plate distance.