Characterization of the Surface Curvature Effect Using LES for a Single Round Impinging Jet

In this paper, wall resolved Large Eddy Simulation is used to study the effect of the surface curvature for two impinging jet configurations. The reference case is a single round jet impinging on a flat plate at a Reynolds number (based on the bulk velocity Ub and the pipe diameter D) Re = 23 000 and for a nozzle to plate distance H = 2D. The results on this configuration have been previously analyzed and validated against experimental results. This paper compares for the same operating point, the flat plate impingement to an impinging jet on a concave hemispherical surface with a relative curvature d/D = 0.089 where d is the concave surface diameter. Mean and Root Mean Square (RMS) quantities are compared to highlight differences and similarities between the two cases. In addition high order statistic such as Skewness of the temporal distribution of wall heat flux is analyzed. Probability density functions (PDF) are also built to further characterize the effect of surface curvature. It is shown that the surface curvature has a destabilizing effect on the vortical structures present in such a flow leading to a modification of the wall heat transfer compared to the flat plate case. The flow topology in the concave case is dominated by a large toroidal stationary vortex. This vortex generates a natural confinement that causes the increase of the mean temperature of the ambient air around the jet. The main effect is the reduction of the capacity of the vortical structures to enhance heat transfer. Finally, the confinement effect combined with the destabilization due to the concave curvature lead to an alleviation of the secondary peak in the Nusselt distribution and a reduction of the heat transfer at the wall.

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Large Eddy Simulation of the Heat Transfer Due to Swirling and Non-Swirling Jet Impingement

Heat Transfer: Volume 2 ◽

10.1115/ht2008-56422 ◽

2008 ◽

Cited By ~ 1

Author(s):

Naseem Uddin ◽

S. O. Neumann ◽

B. Weigand

Keyword(s):

Heat Transfer ◽

Turbulence Models ◽

Jet Impingement ◽

Impinging Jet ◽

Test Case ◽

Complex Flow ◽

Free Jet ◽

Eddy Simulation ◽

Large Eddy ◽

Target Wall

Turbulent impinging jet is a complex flow phenomenon involving free jet, impingement and subsequent wall jet development zones; this makes it a difficult test case for the evaluation of new turbulence models. The complexity of the jet impingement can be further amplified by the addition of the swirl. In this paper, results of Large Eddy Simulations (LES) of swirling and non-swirling impinging jet are presented. The Reynolds number of the jet based on bulk axial velocity is 23000 and target-to-wall distance (H/D) is two. The Swirl numbers (S) of the jet are 0,0.2, 0.47. In swirling jets, the heat transfer at the geometric stagnation zone deteriorates due to the formation of conical recirculation zone. It is found numerically that the addition of swirl does not give any improvement for the over all heat transfer at the target wall. The LES predictions are validated by available experimental data.

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Unsteady Simulations for an Advanced-Louver Cooling Scheme

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-51477 ◽

2008 ◽

Author(s):

Chad X.-Z. Zhang ◽

Sung In Kim ◽

Ibrahim G. Hassan

Keyword(s):

Reynolds Number ◽

Wind Tunnel ◽

Flat Plate ◽

Flow Velocity ◽

Detached Eddy Simulation ◽

Computer Cluster ◽

Vortical Structures ◽

Eddy Simulation ◽

Mainstream Flow ◽

Adiabatic Effectiveness

The performance of a louver cooling scheme on a flat plate was analyzed using Detached Eddy Simulation. It was assumed that the louver cooling scheme was tested in a wind tunnel with the mainstream flow velocity of 20 m/s, equivalent to a Reynolds number of 16200 based on the jet diameter. Turbulence closure was achieved by a Realizable k-ε based DES turbulence model. Solutions of two blowing ratios of 0.5 and 1 were successfully obtained by running parallel on 16 nodes on a computer cluster. The instantaneous flow fields were found to be highly unsteady and oscillatory in nature. It is shown that the fluctuations in the adiabatic effectiveness are mainly caused by the spanwise fluctuation of the coolant jet and the unsteady vortical structures created by the interaction of the jet and the mainstream.

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Studies on Heat Transfer by Impinging Jet : 1st Report Flow and Mass Transfer by Two-Dimensional Air Jet Directed Normal to a Flat Plate

Transactions of the Japan Society of Mechanical Engineers ◽

10.1299/kikai1938.35.1053 ◽

1969 ◽

Vol 35 (273) ◽

pp. 1053-1061 ◽

Cited By ~ 7

Author(s):

Masaya KUMADA ◽

Ikuo MABUCHI

Keyword(s):

Heat Transfer ◽

Mass Transfer ◽

Flat Plate ◽

Impinging Jet ◽

Two Dimensional ◽

Air Jet

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Large Eddy Simulation of Round Impinging Jets With Large Stand-Off Distance

Volume 7: Fluids Engineering Systems and Technologies ◽

10.1115/imece2014-37194 ◽

2014 ◽

Author(s):

Mehrdad Shademan ◽

Vesselina Roussinova ◽

Ron Barron ◽

Ram Balachandar

Keyword(s):

Large Eddy Simulation ◽

Flow Characteristics ◽

Impinging Jet ◽

Impinging Jets ◽

Vortical Structures ◽

Nozzle Height ◽

Eddy Simulation ◽

Large Eddy ◽

The Mean ◽

Good Agreement

Large Eddy Simulation (LES) has been carried out to study the flow of a turbulent impinging jet with large nozzle height-to-diameter ratio. The dynamic Smagorinsky model was used to simulate the subgrid-scale stresses. The jet exit Reynolds number is 28,000. The study presents a detailed evaluation of the flow characteristics of an impinging jet with nozzle height of 20 diameters above the plate. Results of the mean normalized centerline velocity and wall shear stress show good agreement with previous experiments. Analysis of the flow field shows that vortical structures generated due to the Kelvin-Helmholtz instabilities in the shear flow close to the nozzle undergo break down or merging when moving towards the plate. Unlike impinging jets with small stand-off distance where the ring-like vortices keep their interconnected shape upon reaching the plate, no sign of interconnection was observed on the plate for this large stand-off distance. A large deflection of the jet axis was observed for this type of impinging jet when compared to the cases with small nozzle height-to-diameter ratios.

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Heat Transfer Characteristics of an Inclined Impinging Jet on a Curved Surface in Crossflow

Journal of Heat Transfer ◽

10.1115/1.4027389 ◽

2014 ◽

Vol 136 (8) ◽

Cited By ~ 10

Author(s):

X. L. Wang ◽

H. B. Yan ◽

T. J. Lu ◽

S. J. Song ◽

T. Kim

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Flat Plate ◽

Local Heat Transfer ◽

Impinging Jet ◽

Local Heat ◽

Curved Surface ◽

Heat Transfer Characteristics ◽

Potential Core ◽

Transfer Characteristics

This study reports on heat transfer characteristics on a curved surface subject to an inclined circular impinging jet whose impinging angle varies from a normal position θ = 0 deg to θ = 45 deg at a fixed jet Reynolds number of Rej = 20,000. Three curved surfaces having a diameter ratio (D/Dj) of 5.0, 10.0, and infinity (i.e., a flat plate) were selected, each positioned systematically inside and outside the potential core of jet flow where Dj is the circular jet diameter. Present results clarify similar and dissimilar local heat transfer characteristics on a target surface due to the convexity. The role of the potential core is identified to cause the transitional response of the stagnation heat transfer to the inclination of the circular jet. The inclination and convexity are demonstrated to thicken the boundary layer, reducing the local heat transfer (second peaks) as opposed to the enhanced local heat transfer on a flat plate resulting from the increased local Reynolds number.

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Large eddy simulation of saw tooth plasma actuator for improving film cooling efficiency

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650917704596 ◽

2017 ◽

Vol 231 (5) ◽

pp. 357-370 ◽

Cited By ~ 4

Author(s):

Guozhan Li ◽

Jianyang Yu ◽

Fu Chen ◽

Huaping Liu ◽

Yanping Song ◽

...

Keyword(s):

Large Eddy Simulation ◽

Flat Plate ◽

Film Cooling ◽

Three Dimensional ◽

Plasma Actuator ◽

Cooling Efficiency ◽

Flow Topology ◽

Eddy Simulation ◽

Large Eddy ◽

Film Cooling Efficiency

This paper presents results on a saw tooth plasma actuator for the inducement of flow topology and the improvement of flat plate film cooling efficiency. A phenomenological plasma model is constructed to generate the three-dimensional plasma force vectors of the saw tooth plasma actuator. The dynamics of airflow induced by the saw tooth plasma actuator on a flat plate in quiescent air are numerically investigated. The results show that the saw tooth plasma actuator pushes the fluids in all three directions and induces a three-dimensional jet flow with counter rotating streamwise oriented vortices that propagate downstream. The flow field characteristics of both cylindrical hole with and without the saw tooth plasma actuator are studied by large eddy simulation, and a comparison is made. The saw tooth plasma actuator improves the cold jet adherent performance and promotes the spanwise spreading rate of the coolant. Meanwhile, the streamwise vortices induced by the saw tooth plasma actuator suppress the development of counter-rotating vortex pair, thus delaying the diffusion of coolant in the crossflow. Accordingly, the centerline cooling efficiency and the spanwise-averaged cooling efficiency are improved by 36% and 144% at x/ d = 15, compared with the baseline case without the saw tooth plasma actuator.

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