A Turbulence Scaling Factor that converts laminar solutions to turbulent solutions

Mapping Intimacies ◽

10.21203/rs.3.rs-86923/v1 ◽

2020 ◽

Author(s):

Huseyin Onur

Keyword(s):

Heat Transfer ◽

Fractal Dimension ◽

Skin Friction ◽

Stokes Equations ◽

Scaling Factor ◽

Transfer Coefficients ◽

Roughness Effects ◽

Turbulent Eddies ◽

Effective Roughness ◽

Turbulence Scaling

Abstract The quest to understand turbulent flows continues to be as important as it was during the previous century. Present work shows that if a 'laminar' solution to Navier -Stokes equations can be found then skin friction and heat transfer coefficients for the turbulent case can readily be obtained. There is no need for Reynolds averaging and turbulence modelling. This can be done by defining a turbulence scaling factor which converts 'laminar' diffusivities to turbulent diffusivities. Using turbulent diffusivities in the laminar skin friction coefficient formula and laminar heat transfer coefficient formula gives the corresponding turbulent formula. Five different test cases with credible experimental measurements have been used to show the success of the present approach. This work also gives the lengths of internally generated turbulent eddies and roughness created turbulent eddies. If main flow mixes the turbulent eddies , smaller eddies are merged by the larger ones and this is the suggested model for roughness effects which dominates at large Reynolds numbers. A single effective roughness which determines the friction factor has also been obtained and the fractal dimension of turbulence is given as power to Reynolds number. This fractal dimension is in accord with literature for turbulent/non-turbulent interfaces.

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Modeling and analysis of solar air channels with attachments of different shapes

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-08-2018-0435 ◽

2019 ◽

Vol 29 (5) ◽

pp. 1815-1845 ◽

Cited By ~ 10

Author(s):

Younes Menni ◽

Ahmed Azzi ◽

A. Chamkha

Keyword(s):

Heat Transfer ◽

Stokes Equations ◽

Research Work ◽

Convection Heat Transfer ◽

Navier Stokes ◽

Transfer Coefficients ◽

Navier Stokes Equations ◽

Content Type ◽

Modeling And Analysis ◽

Air Channels

Purpose This paper aims to report the results of numerical analysis of turbulent fluid flow and forced-convection heat transfer in solar air channels with baffle-type attachments of various shapes. The effect of reconfiguring baffle geometry on the local and average heat transfer coefficients and pressure drop measurements in the whole domain investigated at constant surface temperature condition along the top and bottom channels’ walls is studied by comparing 15 forms of the baffle, which are simple (flat rectangular), triangular, trapezoidal, cascaded rectangular-triangular, diamond, arc, corrugated, +, S, V, double V (or W), Z, T, G and epsilon (or e)-shaped, with the Reynolds number changing from 12,000 to 32,000. Design/methodology/approach The baffled channel flow model is controlled by the Reynolds-averaged Navier–Stokes equations, besides the k-epsilon (or k-e) turbulence model and the energy equation. The finite volume method, by means of commercial computational fluid dynamics software FLUENT is used in this research work. Findings Over the range investigated, the Z-shaped baffle gives a higher thermal enhancement factor than with simple, triangular, trapezoidal, cascaded rectangular-triangular, diamond, arc, corrugated, +, S, V, W, T, G and e-shaped baffles by about 3.569-20.809; 3.696-20.127; 3.916-20.498; 1.834-12.154; 1.758-12.107; 7.272-23.333; 6.509-22.965; 8.917-26.463; 8.257-23.759; 5.513-18.960; 8.331-27.016; 7.520-26.592; 6.452-24.324; and 0.637-17.139 per cent, respectively. Thus, the baffle of Z-geometry is considered as the best modern model of obstacles to significantly improve the dynamic and thermal performance of the turbulent airflow within the solar channel. Originality/value This analysis reports an interesting strategy to enhance thermal transfer in solar air channels by use of attachments with various shapes

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Heat Transfer Enhancement by Turbulent Impinging Jets

10.1115/imece2000-1279 ◽

2000 ◽

Author(s):

M. Kumagai ◽

R. S. Amano ◽

M. K. Jensen

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Stokes Equations ◽

Local Heat Transfer ◽

Local Heat ◽

Impinging Jets ◽

Transfer Model ◽

Transfer Coefficients ◽

Heat Transfer Coefficients

Abstract A numerical and experimental investigation on cooling of a solid surface was performed by studying the behavior of an impinging jet onto a fixed flat target. The local heat transfer coefficient distributions on a plate with a constant heat flux were computationally investigated with a normally impinging axisymmetric jet for nozzle diameter of 4.6mm at H/d = 4 and 10, with the Reynolds numbers of 10,000 and 40,000. The two-dimensional cylindrical Navier-Stokes equations were solved using a two-equation k-ε turbulence model. The finite-volume differencing scheme was used to solve the thermal and flow fields. The predicted heat transfer coefficients were compared with experimental measurements. A universal function based on the wave equation was developed and applied to the heat transfer model to improve calculated local heat transfer coefficients for short nozzle-to-plate distance (H/d = 4). The differences between H/d = 4 and 10 due to the correlation among heat transfer coefficient, kinetic energy and pressure were investigated for the impingement region. Predictions by the present model show good agreement with the experimental data.

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Dufour and Soret effects on Al2O3-water nanofluid flow over a moving thin needle: Tiwari and Das model

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-03-2020-0177 ◽

2020 ◽

Vol ahead-of-print (ahead-of-print) ◽

Cited By ~ 1

Author(s):

Iskandar Waini ◽

Anuar Ishak ◽

Ioan Pop

Keyword(s):

Heat Transfer ◽

Mass Transfer ◽

Transfer Coefficient ◽

Mass Transfer Coefficient ◽

Skin Friction ◽

Temporal Stability ◽

Physical Parameters ◽

Transfer Coefficients ◽

Nanofluid Flow ◽

Content Type

Purpose This paper aims to examine the effect of Dufour and Soret diffusions on Al2O3-water nanofluid flow over a moving thin needle by using the Tiwari and Das model. Design/methodology/approach The governing equations are reduced to the similarity equations using similarity transformations. The resulting equations are programmed in Matlab software through the bvp4c solver to obtain their solutions. The features of the skin friction, heat transfer and mass transfer coefficients, as well as the velocity, temperature and concentration profiles for different values of the physical parameters, are analysed and discussed. Findings The non-uniqueness of the solutions is observed for a certain range of the physical parameters. The authors also notice that the bifurcation of the solutions occurs in which the needle moves toward the origin (λ < 0). It is discovered that the first branch solutions of the skin friction coefficient and the heat transfer coefficients increase, but the mass transfer coefficient decreases in the presence of nanoparticle. Additionally, the simultaneous effect of Dufour and Soret diffusions tends to enhance the heat transfer coefficient; however, dual behaviours are observed for the mass transfer coefficient. Further analysis shows that between the two solutions, only one of them is stable and thus physically reliable in the long run. Originality/value The problem of Al2O3-water nanofluid flow over a moving thin needle with Dufour and Soret effects are the important originality of the present study. Besides, the temporal stability of the dual solutions is examined for time.

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Heat Transfer Enhancement by Shot Peening of Stainless Steel

Coatings ◽

10.3390/coatings10060584 ◽

2020 ◽

Vol 10 (6) ◽

pp. 584

Author(s):

Pramote Koowattanasuchat ◽

Numpon Mahayotsanun ◽

Sedthawatt Sucharitpwatskul ◽

Sasawat Mahabunphachai ◽

Kuniaki Dohda

Keyword(s):

Heat Transfer ◽

Surface Roughness ◽

Stainless Steel ◽

Process Parameters ◽

Shot Peening ◽

Cfd Simulation ◽

Cost Effective ◽

Transfer Coefficients ◽

Roughness Effects ◽

Heat Transfer Efficiency

In heat exchange applications, the heat transfer efficiency could be improved by surface modifications. Shot peening was one of the cost-effective methods to provide different surface roughness. The objectives of this study were (1) to investigate the influences of the surface roughness on the heat transfer performance and (2) to understand how the shot peening process parameters affect the surface roughness. The considered specimens were 316L stainless steel hollow tubes having smooth and rough surfaces. The computational fluid dynamics (CFD) simulation was used to observe the surface roughness effects. The CFD results showed that the convective heat transfer coefficients had linear relationships with the peak surface roughness (Rz). Finite element (FE) simulation was used to determine the effects of the shot peening process parameters. The FE results showed that the surface roughness was increased at higher sandblasting speeds and sand diameters.

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Direct numerical simulation of turbulent heat transfer across a sheared wind-driven gas–liquid interface

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.554 ◽

2016 ◽

Vol 804 ◽

pp. 646-687 ◽

Cited By ~ 10

Author(s):

Ryoichi Kurose ◽

Naohisa Takagaki ◽

Atsushi Kimura ◽

Satoru Komori

Keyword(s):

Heat Transfer ◽

Numerical Simulation ◽

Mass Transfer ◽

Heat Flux ◽

Streamwise Velocity ◽

Liquid Interface ◽

Turbulent Heat Transfer ◽

Turbulent Heat ◽

Transfer Coefficients ◽

Turbulent Eddies

Turbulent heat transfer across a sheared wind-driven gas–liquid interface is investigated by means of a direct numerical simulation of gas–liquid two-phase turbulent flows under non-breaking wave conditions. The wind-driven wavy gas–liquid interface is captured using the arbitrary Lagrangian–Eulerian method with boundary-fitted coordinates on moving grids, and the temperature fields on both the gas and liquid sides, and the humidity field on the gas side are solved. The results show that although the distributions of the total, latent, sensible and radiative heat fluxes at the gas–liquid interface exhibit streak features such that low-heat-flux regions correspond to both low-streamwise-velocity regions on the gas side and high-streamwise-velocity regions on the liquid side, the similarity between the heat-flux streak and velocity streak on the gas side is more significant than that on the liquid side. This means that, under the condition of a fully developed wind-driven turbulent field on both the gas and liquid sides, the heat transfer across the sheared wind-driven gas–liquid interface is strongly affected by the turbulent eddies on the gas side, rather than by the turbulent eddies and Langmuir circulations on the liquid side. This trend is quite different from that of the mass transfer (i.e. $\text{CO}_{2}$ gas). This is because the resistance to heat transfer is normally lower than the resistance to mass transfer on the liquid side, and therefore the heat transfer is controlled by the turbulent eddies on the gas side. It is also verified that the predicted total heat, latent heat, sensible heat and enthalpy transfer coefficients agree well with previously measured values in both laboratory and field experiments. To estimate the heat transfer coefficients on both the gas and liquid sides, the surface divergence could be a useful parameter, even when Langmuir circulations exist.

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Numerical Computation of Roughness Effects on Heat Transfer and Hydrodynamic Characteristics in Microchannels

ASME 4th International Conference on Nanochannels, Microchannels, and Minichannels, Parts A and B ◽

10.1115/icnmm2006-96076 ◽

2006 ◽

Author(s):

Heming Yun ◽

Lin Cheng ◽

Liqiu Wang ◽

Binjian Chen

Keyword(s):

Heat Transfer ◽

Surface Roughness ◽

Stokes Equations ◽

Three Dimensional ◽

Navier Stokes ◽

Hydrodynamic Characteristics ◽

Roughness Effects ◽

Navier Stokes Equations ◽

Experimental Heat ◽

Macro Scale

In the present paper we focus our attention on the analysis of surface roughness effects. In the process of numerical simulation, a finite-volume method was used to solve the three-dimensional Navier-Stokes equations and energy equation. In turbulent region, wall-function was used to solve the temperature and velocity of coolant in the area near the wall. In all computational regions, the fluid-solid Conjugate heat transfer is used to solve the microchannel heat transfer problems. In conclusion the effect of surface roughness on heat transfer and pressure drop can not be neglected. And one should be very careful in ascribing the roughness effect to the discrepancies between experimental heat transfer and the prediction for standard macro scale channels.

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Effects of Inlet Swirl Angle on Flow and Heat Transfer in Contoured Turbine Nozzle Guide Vanes

10.1115/imece2001/htd-24312 ◽

2001 ◽

Author(s):

Y.-L. Lin ◽

H. J. Schock ◽

T. I-P. Shih ◽

R. S. Bunker

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Stokes Equations ◽

Secondary Flows ◽

Stagnation Zone ◽

Transfer Coefficients ◽

Pressure Surface ◽

Flow And Heat Transfer ◽

Swirl Angle ◽

Inlet Swirl

Abstract Computations, based on the ensemble-averaged compressible Navier-Stokes equations closed by the shear-stress transport (SST) model of turbulence, were performed to investigate the effects of inlet swirl angle on the three-dimensional flow and heat transfer in two contoured endwall configurations. Swirl angles investigated include three constant angles (0°, 15°, 30°) and a linearly varying angle from +30° at one endwall to −30° at the other. For all swirl angles, the mass-flow rate through the nozzle was fixed so that the higher the swirl angle, the higher is the velocity magnitude. Of the two endwalls investigated, one has all of the contouring upstream of the airfoil (C1), and another has contouring that starts upstream of the airfoil and continues until the airfoil’s trailing edge (C2). Computed results show that at all swirl angles investigated, the C2 configuration was able to reduce significantly secondary flows on the contoured endwall. Results also show that with reduced secondary flows, the heat-transfer coefficients are also reduced on the suction surface next to the juncture, where the airfoil meets the contoured endwall. On aerodynamics, the C2 configuration was found to produce essentially the same lift as the C1 configuration, but does so with less loss in stagnation pressure. For the C1 configuration, secondary flows are quite pronounced, and they increase slightly in size and in magnitude when swirl angle is increased. However, aerodynamic loss and surface heat transfer were found to decrease with increase in swirl angle. One explanation is that increasing the swirl angle shifted the stagnation zone downstream on the pressure surface to a flatter portion of the airfoil, producing a thicker boundary layer at the stagnation zone, and this changed considerably the evolution of the turbulent boundary layer. When the swirl angle varied linearly from +30° to −30°, increasing the velocity component towards the pressure surface was found to enhance instead of suppress the formation of secondary flows.

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Unsteady Stagnation-Point Flow and Heat Transfer Over a Permeable Exponential Stretching/Shrinking Sheet in Nanofluid with Slip Velocity Effect: A Stability Analysis

Applied Sciences ◽

10.3390/app8112172 ◽

2018 ◽

Vol 8 (11) ◽

pp. 2172 ◽

Cited By ~ 10

Author(s):

Nor Dzulkifli ◽

Norfifah Bachok ◽

Nor Yacob ◽

Norihan Md Arifin ◽

Haliza Rosali

Keyword(s):

Heat Transfer ◽

Stability Analysis ◽

Skin Friction ◽

Stagnation Point ◽

Velocity Slip ◽

Shrinking Sheet ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Flow And Heat Transfer ◽

Exponential Stretching

A model of unsteady stagnation-point flow and heat transfer over a permeable exponential stretching/shrinking sheet with the presence of velocity slip is considered in this paper. The nanofluid model proposed by Tiwari and Das is applied where water with Prandtl number 6.2 has been chosen as the base fluid, while three different nanoparticles are taken into consideration, namely Copper, Alumina, and Titania. The ordinary differential equations are solved using boundary value problem with fourth order accuracy (bvp4c) program in Matlab to find the numerical solutions of the skin friction and heat transfer coefficients for different parameters such as stretching/shrinking, velocity slip, nanoparticle volume fraction, suction/injection, and also different nanoparticles, for which the obtained results (dual solutions) are presented graphically. The velocity and temperature profiles are presented to show that the far field boundary conditions are asymptotically fulfilled, and validate the findings of dual solutions as displayed in the variations of the skin friction and heat transfer coefficients. The last part is to perform the stability analysis to determine a stable and physically-realizable solution.

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The Calculation of Heat Transfer Coefficients from Skin Friction Coefficients in the Compressible Laminar Boundary Layer on an Aerofoil

Aeronautical Quarterly ◽

10.1017/s0001925900004649 ◽

1968 ◽

Vol 19 (3) ◽

pp. 243-253 ◽

Cited By ~ 1

Author(s):

R. E. Luxton

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Pressure Gradient ◽

Skin Friction ◽

Laminar Boundary Layer ◽

Strong Dependence ◽

Transfer Coefficients ◽

Friction Coefficients ◽

Heat Transfer Coefficients ◽

Numerical Simulation of Flow Field and Heat Transfer of Streamlined Cylinders in Crossflow

Heat Transfer: Volume 3 ◽

10.1115/ht2005-72024 ◽

2005 ◽

Cited By ~ 3

Author(s):

Zhihua Li ◽

Jane Davidson ◽

Susan Mantell

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Pressure Drop ◽

Circular Cylinder ◽

Average Nusselt Number ◽

Stokes Equations ◽

Local Heat Transfer ◽

Published Data ◽

Transfer Coefficients ◽

Axis Ratio

The use of streamlined tubes to reduce pressure drop across polymer tube bundles is considered because of the relative ease of fabrication. The drag and convective heat transfer coefficients along the outer surface of lenticular and elliptical tubes with minor-to-major axis ratios of 0.3, 0.5, and 0.8 are determined numerically for cross-flow Reynolds numbers from 500 to 10,000. An isothermal surface is assumed. The two-dimensional, unsteady Navier-Stokes equations and energy equation are solved using the finite volume method. Laminar flow is assumed from the front stagnation point up to the point of separation. Turbulent flow in the wake is resolved using the shear stress transport k-omega model. Local heat transfer, pressure and friction coefficients as well as a total drag coefficient and average Nusselt number are presented. The results for streamlined tubes are compared to published data for circular and elliptical cylinders. Drag of the elliptical and lenticular cylinders is similar and lower than a circular cylinder. Reductions in drag may be increased by making the streamlined cylinders more slender. Over the range of Reynolds number considered, an elliptical cylinder with an axis ratio equal to 0.5 reduces pressure drop by 30 to 40 percent compared to that of a circular cylinder. The lenticular and elliptical geometries have nearly identical average of Nusselt number. The average Nusselt number of an elliptical or lenticular cylinder with axis ratio of 0.5 and 0.3 is 15 to 35% lower than that of a circular cylinder. A case study for an automotive radiator is presented to illustrate comparison of shaped and circular tubes in terms of both heat transfer and pressure drop.

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