Computational Study of Slot Jet Impingement Heat Transfer on a Combined Dimpled and Protruded Concave Surface

Impinging heat transferred by a pulsed jet induced by a six-chevron nozzle on a semicylindrical concave surface is investigated by varying jet Reynolds numbers (5000 ≤ Re ≤ 20,000), operational frequencies (0 Hz ≤ f ≤ 25 Hz), and dimensionless nozzle-to-surface distances (1 ≤ H/d ≤ 8) while fixing the duty cycle as DC = 0.5. The semicylindrical concave surface has a cylinder diameter-to-nozzle diameter ratio (D/d) of 10. The results show that the nozzle-to-surface distance has a significant impact on the impingement heat transfer of the pulsed chevron jet. An optimal nozzle-to-surface distance for achieving the maximum stagnation Nusselt number appears at H/d = 6. In the wall jet zone, the averaged Nusselt number is the largest at H/d = 2 and the smallest at H/d = 8. In comparison with the chevron steady jet impingement, the effect of nozzle-to-surface distance on the convective heat transfer becomes less notable for the pulsed chevron jet impingement. The stagnation Nusselt number under the pulsed chevron jet impingement is mostly less than that under the chevron steady jet impingement. However, at H/d = 8, the pulsed chevron jet is more effective than the steady jet. This study confirmed that the pulsed chevron jet produced higher azimuthally averaged Nusselt numbers than the steady chevron jet in the wall jet flow zone at large nozzle-to-surface distances. The stagnation Nusselt numbers by the pulsed chevron jet impingement have a maximum reduction of 21.0% (f = 20 Hz, H/d = 4, and Re = 2000) compared with that of the steady chevron jet impingement. Also, the pulsed chevron jet impingement heat transfer on a concave surface is less effective compared to a flat surface. The stagnation Nusselt numbers on the semicylindrical concave surface have a maximum reduction of about 37.7% (f = 20 Hz, H/d = 8, and Re = 5000) compared with that on the flat surface.

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Computational Study of Micro-Jet Impingement Heat Transfer in a High Pressure Turbine Vane

Volume 5: Heat Transfer, Parts A and B ◽

10.1115/gt2011-45267 ◽

2011 ◽

Author(s):

Karan Anand ◽

B. A. Jubran

Keyword(s):

Heat Transfer ◽

Computational Study ◽

Jet Impingement ◽

Local Heat Transfer ◽

Local Heat ◽

Spanwise Direction ◽

Constant Property ◽

Impingement Heat Transfer ◽

Turbine Vane ◽

Volume Method

The purpose of this numerical investigation is to study the micro-jet impingement heat transfer characteristics and hydromechanics in a 3-D, actual-shaped turbine vane geometry. No concession is made on either the skewness or curvature profile of the airfoil in the streamwise direction, nor to the lean, airfoil twist or tapering of the vane in the spanwise direction. The problem on hand consists of a constant property flow of air via an array of 42 round micro jets impinging onto the inner surface of the airfoil. For simplicity, validation and better understanding of the nature of impingement heat transfer, the airfoil surfaces are provided with a constant temperature boundary condition. Validation is performed against existing numerical results on a simplified model with no spanwise tapering or twisting. The modeled volume spans a total of 12D and consists of three rows of jets; each row contains 14 inline jets. Governing equations are solved using a finite volume method in FLUENT. Effects of jet inclination (+45° and −45° inclinations) and decrease in nozzle diameter (0.51, 0.25 and 0.125 mm) are studied. Inclination of −45° produced enhanced mixing and secondary peaks with marginal decrease in stagnation values. The effect of reducing the diameter of the jets yielded positive results; the tapering effect too enhanced the local heat transfer values, which is attributed to the increase in local velocities at jet exit.

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A detailed analysis of flow and heat transfer characteristics under a turbulent intermittent jet impingement on a concave surface

Thermal Science ◽

10.2298/tsci200729334h ◽

2021 ◽

pp. 334-334

Author(s):

Ali Hajimohammadi ◽

Mehran Zargarabadi ◽

Javad Mohammadpour

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Nusselt Number ◽

Average Nusselt Number ◽

Computational Study ◽

Control Volume ◽

Simple Algorithm ◽

Jet Impingement ◽

Concave Surface ◽

Flow And Heat Transfer

A computational study is carried out of the three-dimensional flow field and heat transfer under a turbulent intermittent circular jet impingement on a concave surface. The control-volume procedure with the SIMPLE algorithm is employed to solve the unsteady RANS (use full form) equations. The RNG k-? model is implemented to simulate turbulence due to its success in predicting similar flows. The numerical results are validated by comparing them with the experimental data. The effects of jet Reynolds number and oscillation frequency on the flow and heat transfer are evaluated. The profiles of instantaneous and time-averaged Nusselt numbers exhibit different trends in axial (x) and circumferential (s) directions. It is found that increasing frequency from 50 to 200 Hz results in considerable time-averaged Nusselt number enhancement in both axial and curvature directions. The intermittent jet at a frequency of 200 Hz enhances the total average Nusselt number by 51.4%, 40%, and 33.7% compared to the steady jet values at jet Reynolds numbers of 10000, 23000, and 40000, respectively. In addition, a correlation for the average Nusselt number is proposed depending on the Reynolds number and the Strouhal number.

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