Effect of cylinder corner radius and attack angle on heat transfer and flow topology

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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The Numerical Simulation Research on Heat Transfer Enhancement of the Interpolation-Tubular Air Pre-Heater with Semi-Elliptic Cylinder Shell Vortex Generator

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.397-400.230 ◽

2013 ◽

Vol 397-400 ◽

pp. 230-234

Author(s):

De Fan Qing ◽

Qing Feng Ai

Keyword(s):

Heat Transfer ◽

Heat Transfer Enhancement ◽

Vortex Generator ◽

Elliptic Cylinder ◽

Attack Angle ◽

Width Ratio ◽

Transfer Enhancement ◽

Simulation Research ◽

Number Range ◽

Dip Angle

The semi-elliptic cylinder shell vortex generator set in the interpolation-tubular air pre-heater was studied. And by changing the high-width Ratiov, dip angleα, attack angleβ, spacingsof vortex generator to research the heat transfer and resistance properties under different working conditions, and the optimization structure of vortex generator was determined. The heating medium of the air pre-heater is the flue gas that passes across tube outside, and the cooling air as the cooling medium in the tube longitudinal scoured. The Reynolds number range is 25000 ~ 40000. The research shows that: semi-elliptic cylinder vortex generator can obviously improve the heat transfer performance, the optimization structure of the semi-elliptic cylinder vortex generator: high-width ratiov= 0.45, attack angleβ= 65 °, dip angleα= 15 °, spans= 90 mm, the heat transfer enhancement comprehensive effect raised about 43.2%~72.6%.

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Flow Visualization and Conjugate Heat Transfer Study From Shower Head Impinging Jets

Volume 5: Heat Transfer, Parts A and B ◽

10.1115/gt2011-45098 ◽

2011 ◽

Cited By ~ 3

Author(s):

Rajesh Kumar Panda ◽

B. V. S. S. S. Prasad

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Flow Visualization ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Nodal Point ◽

Weighted Average ◽

Bottom Surface ◽

Separation Flow ◽

Flow Topology

Computational and experimental investigations on a flat circular disk are reported with a constant heat flux imposed on its bottom surface and a shower head of air jets impinging on the top surface. The shower head consists of a central jet surrounded by four neighboring perimeter jets. Lamp black flow visualization technique and computations using shear stress transport (SST) κ-ω turbulence model are employed to describe the complex interaction of the wall jets and the associated flow structure. Thermochromic liquid crystal measurement technique is used for surface temperature measurement. The formations of saddle point, nodal point of attachment, nodal point of separation, flow separation line and the up-wash flow are identified. It is observed that the flow topology is practically independent of Reynolds number within the investigated range but is significantly altered with the spacing between the jet orifice and the target surface. A strong correlation between the Nusselt number and the pressure distribution is noticed. Local variation of heat transfer rate with varying plate spacing to jet diameter ratio is significant but its effect on the area weighted average heat transfer rate is small. When compared with a single jet of equal mass flow rate and Reynolds number, the shower head jets provide higher heat transfer rate but require more power for pumping.

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Heat Transfer Augmentation and Flow Visualization With Delta Winglets in a Tube: A Numerical Approach

ASME 2020 Heat Transfer Summer Conference ◽

10.1115/ht2020-8927 ◽

2020 ◽

Author(s):

Md. Islam ◽

Liang Guangda ◽

Md. Mahbub Alam

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Thermal Performance ◽

Performance Enhancement ◽

Swirling Flow ◽

Circular Tube ◽

Vortex Generator ◽

Attack Angle ◽

Maximum Enhancement ◽

Longitudinal Vortices

Abstract In this research, heat transfer and pressure penalty from a circular tube with delta winglets insert are numerically investigated through Computational Fluid Dynamics (CFD) methodology. Numerical analysis with and without vortex generators (VGs) insert in a tube are done for a turbulent air flow, Reynolds number ranging from 6000 to 33000, under constant heat flux condition on the circular tube model surface. In our current research, we employed the shear stress transport (SST) k-omega model. The Nusselt number and friction factor results show the influence of the VGs insert on thermal performance. Effects of different winglet attack angles and blockage ratios on thermal performance enhancement were examined. Thermal performance is enhanced 5.1–30.7% using winglets in a tube. It is observed that small blockage ratio, B = 0.1 performed better than its counterpart of 0.2 and 0.3 for all the Reynolds number and for the same attack angle. The attack angle β = 15° and 30° showed better thermal performance enhancement at lower Re while at higher Re, β = 15° showed better performance. The maximum enhancement obtained for β = 30° and B = 0.1. Winglet vortex generator could create swirling flow when attack angle is 0 or 15°. When attack angle is increased, both swirling flow and longitudinal vortices appeared. At attack angle of 45°, large longitudinal vortices was found.

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Study of Flow and Heat Transfer Characteristics of non-periodical attack angle in Narrow Rectangular Channel with Longitudinal Vortex generators

10.1063/1.3366419 ◽

2010 ◽

Author(s):

L. Wang ◽

J. Huang ◽

Liejin Guo ◽

D. D. Joseph ◽

Y. Matsumoto ◽

...

Keyword(s):

Heat Transfer ◽

Rectangular Channel ◽

Attack Angle ◽

Vortex Generators ◽

Longitudinal Vortex ◽

Heat Transfer Characteristics ◽

Transfer Characteristics ◽

Flow And Heat Transfer

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Turbulent spot flow topology and mechanisms for surface heat transfer

Journal of Fluid Mechanics ◽

10.1017/s0022112008002838 ◽

2008 ◽

Vol 612 ◽

pp. 81-105 ◽

Cited By ~ 8

Author(s):

D. R. SABATINO ◽

C. R. SMITH

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Turbulent Boundary Layer ◽

Surface Heat ◽

Heated Plate ◽

Surface Shear Stress ◽

Turbulent Spot ◽

Flow Topology ◽

Turbulent Spots ◽

Surface Heat Transfer

The properties of artificially initiated turbulent spots over a heated plate were investigated in a water channel. The instantaneous velocity field and surface Stanton number were simultaneously established using a technique that combines particle image velocimetry and thermochromic liquid crystal thermography. Several characteristics of a spot are found to be similar to those of a turbulent boundary layer. The spacing of the surface heat transfer streak patterns within the middle or ‘body’ of a turbulent spot are comparable to the low-speed streak spacing within a turbulent boundary layer. Additionally, the surface shear stress in the same region of a spot is also found to be comparable to a turbulent boundary layer. However, despite these similarities, the heat transfer within the spot body is found to be markedly less than the heat transfer for a turbulent boundary layer. In fact, the highest surface heat transfer occurs at the trailing or calmed region of a turbulent spot, regardless of maturity. Using a modified set of similarity coordinates, instantaneous two-dimensional streamlines suggest that turbulent spots entrain and subsequently recirculate warm surface fluid, thereby reducing the effective heat transfer within the majority of the spot. It is proposed that energetic vortices next to the wall, near the trailing edge of the spot body, are able to generate the highest surface heat transfer because they have the nearest access to cooler free-stream fluid.

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