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1

Effect of D-shaped, reverse D-shaped and U-shaped turbulators in solar air heater on thermo-hydraulic performance

Ghildyal Abhishek, Bisht Vijay Singh, Bhandari Prabhakar, Rawat Kamal Singh

Archives of Thermodynamics

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2023

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Vol. 44, no 2

3--20

EN

As the cost of fuel rises, designing efficient solar air heaters (SAH) becomes increasingly important. By artificially roughening the absorber plate, solar air heaters’ performance can be augmented. Turbulators in different forms like ribs, delta winglets, vortex generators, etc. have been introduced to create local wall turbulence or for vortex generation. In the present work, a numerical investigation on a solar air heater has been conducted to examine the effect of three distinct turbulators (namely D-shaped, reverse D- and U-shaped) on the SAH thermo-hydraulic performance. The simulation has been carried out using the computational fluid dynamics, an advanced and modern simulation technique for Reynolds numbers ranging from 4000 to 18000 (turbulent airflow). For the purpose of comparison, constant ratios of turbulator height/hydraulic diameter and pitch/turbulator height, of 0.021 and 14.28, respectively, were adopted for all SAH configurations. Furthermore, the fluid flow has also been analyzed using turbulence kinetic energy and velocity contours. It was observed that the U-shaped turbulator has the highest value of Nusselt number followed by D-shaped and reverse D-shaped turbulators. However, in terms of friction factor, the D-shaped configuration has the highest value followed by reverse D-shaped and U-shaped geometries. It can be concluded that among all SAH configurations considered, the U-shaped has outperformed in terms of thermohydraulic performance factor.

2

Numerical simulation of 3D flow in VKI-Genoa turbine cascade including laminar-turbulent transition

Yerschov S., Derevyanko A., Yakovlev V., Gryzun M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2016

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Vol. 20, No 1

43--61

EN

This study presents a numerical simulation of a 3D viscous flow in the VKI-Genoa cascade taking into account the laminar-turbulent transition. The numerical simulation is performed using the Reynolds-averaged Navier-Stokes equations and the two-equation k-ω SST turbulence model. The algebraic Production Term Modification model is used for modeling the laminar-turbulent transition. Computations of both fully turbulent and transitional flows are carried out. The Mach number contours, the turbulence kinetic energy, the entropy function as well as the limiting streamlines are presented. Our numerical results demonstrate the influence of the laminar-turbulent transition on the secondary flow pattern. The comparison between the present computational results and the existing experimental and numerical data shows that the proposed approach reflects sufficiently the physics of the laminar-turbulent transition in turbine cascades.

3

Wpływ wysokości obrzeża łopatki na intensywność zawirowań w kanale turbiny gazowej

Wais P.

Rynek Energii

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2015

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Nr 5

95--101

PL

Celem pracy jest numeryczne oszacowanie wpływu wysokości obrzeża na pole prędkości i pole ciśnienia w kanale przepływowym za krawędzią wylotową łopatki turbiny gazowej. Zamodelowano turbulentny przepływ powietrza w prostokątnym tunelu aerodynamicznym, który rozwiązano za pomocą metod numerycznych wykorzystując moduł ANSYS Workbench. Porównano izolinie prędkości otrzymane na drodze obliczeń komputerowych z wartościami prędkości uzyskanymi na podstawie pomiarów eksperymentalnych dla różnych wymiarów geometrii powierzchni obrzeża łopatki. Dodatkowo przedstawiono także izolinie energii kinetycznej turbulencji oraz rozkład ciśnienia statycznego w różnych wysokościach kanału przepływowego. Otrzymane wyniki pozwoliły na analizę wpływu kształtu powierzchni górnej łopatki na intensywność zawirowań za łopatką turbiny gazowej

EN

The flow through the gas turbine blade cascade is investigated numerically in the paper. The aim of the study is to estimate the impact of the rim height to the tip leakage flow rate and the velocity or pressure fields in the gas flow channel after the gas turbine blade cascade. Turbulent air flow in a rectangular wind tunnel is modeled and then is solved by means of numerical methods using ANSYS Workbench module. The velocity field, located at the cascade outlet, is compared to the experimental measurements. Additionally, the turbulence kinetic energy and pressure distribution at different channel sections are added. The results allow analyzing the impact of the shape of the blade tip on the intensity of turbulence in a gas turbine interblade channel.

4

The convection term evaluation of the turbulence kinetic energy balance in a flame with medium density changes

Grodzki G.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

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2012

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Vol. 11, nr 4

43-52

EN

This paper consists of an analysis pertaining to the turbulence kinetic energy balance equation with the acknowledgement of burning medium density change influence. The evaluation of the convection element value and of the density change influence on the turbulence kinetic energy balance has been attempted. Experimental data obtained by means of laser Doppler anemometry and the radial distributions of average temperatures of a burning jet have been exploited in the present paper.

5

Methodology pertaining to component evaluation of turbulence energy balance in a premixed jet flame with dissipation

Grodzki G.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

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2012

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Vol. 11, nr 3

33-44

EN

This paper consists of an analysis of existing methods and their limitations pertaining to defining the dissipation rate as one of the components of the turbulent kinetic energy balance equation. Careful attention has been paid with reference to the method used during tests conducted in a burning round jet by means of laser Doppler anemometry. This paper covers the developed algorithms for digital signal processing of LDA, examples of output data sets for calculations and chosen profiles of energy balance components of dissipation and production.

6

Stable-boundary-layer regimes from the perspective of the low-level jet

Banta R.

Acta Geophysica

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2008

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Vol. 56, no. 1

58-87

EN

This paper reviews results from two field studies of the nocturnal stable atmospheric boundary layer (SBL) over the Great Plains of the United States. Data from a scanning remote-sensing system, a High-Resolution Doppler Lidar (HRDL), provided measurements of mean and turbulent wind components at high spatial and temporal resolution through the lowest 500-1000 m of the atmosphere. This data set has allowed the characteristics of the low-level jet (LLJ) maximum (speed, height, direction) to be documented through entire nights. LLJs form after sunset and pro-duce strong shear in the layer below the LLJ maximum or nose, which is a source of turbulence and mixing in the SBL. Simultaneous HRDL measurements of turbulence quantities related to turbulence kinetic energy (TKE) has allowed the turbulence in the subjet layer to be related to LLJ properties. Turbulence structure was found to be a function of the bulk stability of the subjet layer. For the strong-LLJ (> 15 m s-1), weakly stable cases the strength of the turbulence is proportional to the strength of the LLJ. For these cases with nearly continuous turbulence in the subjet layer, low-level jet scaling, in which lengths are scaled by the LLJ height and velocity variables are scaled by the LLJ speed, was found to be appropriate. For the weak-wind (< 5 m s-1 in the lowest 200 m), very stable boundary layer (vSBL), the boundary layer was found to be very shallow (sometimes < 10 m deep), and turbulent fluxes between the earth's surface and the atmosphere were found to be essentially shut down. For more intermediate wind speeds and stabilities, the SBL shows varying degrees of intermittency due to various mechanisms, including shear-instability and other gravity waves, density currents, and other mesoscale disturbances.

7

Effects of shear in the convective boundary layer: analysis of the turbulent kinetic energy budget

Pino D., Vila-Guerau de Arellano J.

Acta Geophysica

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2008

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Vol. 56, no. 1

167-193

EN

Effects of convective and mechanical turbulence at the entrainment zone are studied through the use of systematic Large-Eddy Simulation (LES) experiments. Five LES experiments with different shear characteristics in the quasisteady barotropic boundary layer were conducted by increasing the value of the constant geostrophic wind by 5 m s-1 until the geostrophic wind was equal to 20 m s-1. The main result of this sensitivity analysis is that the convective boundary layer deepens with increasing wind speed due to the enhancement of the entrainment heat flux by the presence of shear. Regarding the evolution of the turbulence kinetic energy (TKE) budget for the studied cases, the following conclusions are drawn: (i) dissipation increases with shear, (ii) the transport and pressure terms decrease with increasing shear and can become a destruction term at the entrainment zone, and (iii) the time tendency of TKE remains small in all analyzed cases. Convective and local scaling arguments are applied to parameterize the TKE budget terms. Depending on the physical properties of each TKE budget contribution, two types of scaling parameters have been identified. For the processes influenced by mixed-layer properties, boundary layer depth and convective velocity have been used as scaling variables. On the contrary, if the physical processes are restricted to the entrainment zone, the inversion layer depth, the modulus of the horizontal velocity jump and the momentum fluxes at the inversion appear to be the natural choices for scaling these processes. A good fit of the TKE budget terms is obtained with the scaling, especially for shear contribution.