Non-Linear k-ε-ζ-f Model Sensitized to Rotation for Blade Turbine Internal Cooling

2018 ◽  
Author(s):  
Domenico Borello ◽  
Alessandro Salvagni
Keyword(s):  
Heat Transfer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Mutual Influence ◽  
Plane Channel ◽  
Suction Side ◽  
Quadratic Model ◽  
Internal Cooling ◽  
Flow And Heat Transfer ◽  
Non Linear

The need to study flow and heat transfer in turbine blade cooling design calls to develop appropriate modelling approaches able to return accurate predictions at a reduced computational costs. Here we propose and scrutinize a quadratic version of the well-known k-ε-ζ-f RANS turbulence models, aiming at sensitizing the model to the effect of rotation in configurations mimicking the flow in turbine internal cooling. Starting from the evidence that rotation modified turbulent flow through a turbulence suppression (enhancement) on the stabilized (destabilized) surface, we modified the Cμ coefficient present in the formulation of turbulent viscosity introducing a dependence on the strain and vorticity tensors, the latter explicitly including solid body rotation. The proposed model was tested on plane channel and square-sectioned duct flows, and then used for simulating a rib-duct rotating channel. Results are assessed against DNS literature data and properly developed LES computations, by examining flow variables, heat transfer and turbulence budgets. We demonstrate that, as for the channel flows, the proposed quadratic model is able to accurately reproduce velocity, temperature and turbulent variables at various angular velocity regimes. In the duct flow the flow is subjected to the mutual influence vorticity induced by rotation and turbulence anisotropy developing close the walls. In particular, the non-linear rotation-sensitized model is able to reproduce the near-wall turbulent kinetic energy distribution close to the suction side, returning a zero value in the mid-span and a small peak close to the wall on the suction side. Turbulent kinetic energy and temperature budgets analysis demonstrates the capabilities of the model in describing all the terms in the equations. Also if some tuning of the model is required, these analysis showed very encouraging results. In fact if the basic mechanisms of turbulence and heat transfer are properly predicted, then it can be expected that the model can be successfully applied to a set of different cases. For such reason, the model was applied to the analysis of flow and heat transfer in a rotating ribduct with reasonably results.

scholarly journals Oscillator Fin as a Novel Heat Transfer Augmentation Device for Gas Turbine Cooling Applications

1998 ◽  
Author(s):  
Oguz Uzol ◽  
Cengiz Camci
Keyword(s):  
Heat Transfer ◽  
Kinetic Energy ◽  
Gas Turbine ◽  
Turbulent Kinetic Energy ◽  
Stokes Equations ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Internal Cooling ◽  
Pin Fin ◽  
Heat Transfer Augmentation

A new concept for enhanced turbulent transport of heat in internal coolant passages of gas turbine blades is introduced. The new heat transfer augmentation component called “oscillator fin” is based on an unsteady flow system using the interaction of multiple unsteady jets and wakes generated downstream of a fluidic oscillator. Incompressible, unsteady and two dimensional solutions of Reynolds Averaged Navier-Stokes equations are obtained both for an oscillator fin and for an equivalent cylindrical pin fin and the results are compared. Preliminary results show that a significant increase in the turbulent kinetic energy level occur in the wake region of the oscillator fin with respect to the cylinder with similar level of aerodynamic penalty. The new concept does not require additional components or power to sustain its oscillations and its manufacturing is as easy as a conventional pin fin. The present study makes use of an unsteady numerical simulation of mass, momentum, turbulent kinetic energy and dissipation rate conservation equations for flow visualization downstream of the new oscillator fin and an equivalent cylinder. Relative enhancements of turbulent kinetic energy and comparisons of the total pressure field from transient simulations qualitatively suggest that the oscillator fin has excellent potential in enhancing local heat transfer in internal cooling passages without significant aerodynamic penalty.

scholarly journals Discussion on improved method of turbulence model for supercritical water flow and heat transfer

2020 ◽  
Vol 24 (5 Part A) ◽  
pp. 2729-2741
Author(s):  
Zhenchuan Wang ◽  
Guoli Qi ◽  
Meijun Li
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Turbulence Model ◽  
Buoyancy Effect ◽  
Improved Method ◽  
Production Term ◽  
Flow And Heat Transfer ◽  
Effect Model

The turbulence model fails in supercritical fluid-flow and heat transfer simulation, owing to the drastic change of thermal properties. The inappropriate buoyancy effect model and the improper turbulent Prandtl number model are several of these factors lead to the original low-Reynolds number turbulence model unable to predict the wall temperature for vertically heated tubes under the deteriorate heat transfer conditions. This paper proposed a simplified improved method to modify the turbulence model, using the generalized gradient diffusion hypothesis approximation model for the production term of the turbulent kinetic energy due to the buoyancy effect, using a turbulence Prandtl number model for the turbulent thermal diffusivity instead of the constant number. A better agreement was accomplished by the improved turbulence model compared with the experimental data. The main reason for the over-predicted wall temperature by the original turbulence model is the misuse of the buoyancy effect model. In the improved model, the production term of the turbulent kinetic energy is much higher than the results calculated by the original turbulence model, especially in the boundary-layer. A more accurate model for the production term of the turbulent kinetic energy is the main direction of further modification for the low Reynolds number turbulence model.

scholarly journals Simulation of turbulent flow and heat transfer over a backward facing step with ribs turbulators

2011 ◽  
Vol 15 (1) ◽  
pp. 245-255 ◽  
Author(s):  
Khudheyer Mushatet
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Control Volume ◽  
Step Height ◽  
Staggered Grid ◽  
Backward Facing Step ◽  
Flow And Heat Transfer ◽  
Contraction Ratio

Simulation is presented for a backward facing step flow and heat transfer inside a channel with ribs turbulators. The problem was investigated for Reynolds numbers up to 32000. The effect of a step height, the number of ribs and the rib thickness on the flow and thermal field were investigated. The computed results are presented as streamlines counters, velocity vectors and graphs of Nusselt number and turbulent kinetic energy variation. A control volume method employing a staggered grid techniques was imposed to discretize the governing continuity, full Navier Stockes and energy equations. A computer program using a SIMPLE algorithm was developed to handle the considered problem. The effect of turbulence was modeled by using a k-? model with its wall function formulas. The obtained results show that the strength and size of the re-circulation zones behind the step are increased with the increase of contraction ratio(i.e. with the increase of a step height). The size of recirculation regions and the reattachment length after the ribs are decreased with increasing of the contraction ratio. Also the results show that the Reynolds number and contraction ratio have a significant effect on the variation of turbulent kinetic energy and Nusselt number.

Flow and heat transfer of nanofluid in a channel partially filled with porous media considering turbulence effect in pores

2020 ◽  
Vol 98 (3) ◽  
pp. 297-302 ◽  
Author(s):  
Ali Asghar Sedighi ◽  
Zeynab Deldoost ◽  
Bahram Mahjoob Karambasti
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Porous Media ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Skin Friction Coefficient ◽  
Clear Fluid ◽  
Flow And Heat Transfer ◽  
Turbulence Effect ◽  
Flow Cross

The flow and heat transfer of Al2O3–water nanofluid in a channel partially filled with porous media is investigated numerically. The turbulence effect in the porous media is taken under consideration in this article. A simple case is simulated first to evaluate the accuracy of the results in comparison with the available data. The turbulent kinetic energy profile is investigated at a flow cross section. The results show that the maximum turbulent kinetic energy occurs in the clear fluid region in the vicinity of the porous media region. The turbulent kinetic energy is a decreasing function of the porosity of the porous medium. The effect of porosity on the variation of turbulent kinetic energy decreases with the increase in the porosity of the porous medium. The turbulent kinetic energy in clear fluid and porous media regions decreases with the increase in nanofluid concentration from 0.01 to 0.03, and it increases with the increase in nanofluid concentration from 0.03 to 0.05. The temperature of the nanofluid increases with the increase in the nanofluid concentration and decrease in the porosity of porous media. It is shown that for this case, with the increase in nanofluid concentration and porosity of porous media, the skin friction coefficient increases and the Nusselt number decreases.

Rotating Effect on Fluid Flow in a Smooth Duct With a 180-Deg Sharp Turn

2000 ◽  
Author(s):  
Chung-Chu Chen ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Kinetic Energy ◽  
Secondary Flow ◽  
Turbulent Kinetic Energy ◽  
Turbine Blades ◽  
Outer Part ◽  
Intensity Level ◽  
Mean Velocity ◽  
High Heat Transfer ◽  
Sharp Turn

Laser-Doppler velocimetry (LDV) measurements are presented of turbulent flow in a two-pass square-sectioned duct simulating the coolant passages employed in gas turbine blades under rotating and non-rotating conditions. For all cases studied, the Reynolds number characterized by duct hydraulic diameter (Dh) and bulk mean velocity (Ub) was fixed at 1 × 104. The rotating case had a range of rotation number (Ro = ΩDh/Ub) from 0 to 0.2. It is found that both the skewness of streamwise mean velocity and magnitude of secondary-flow velocity increase linearly, and the magnitude of turbulence intensity level increases non-linearly with increasing Ro. As Ro is increased, the curvature induced symmetric Dean vortices in the turn for Ro = 0 is gradually dominated by a single vortex most of which impinges directly on the outer part of leading wall. The high turbulent kinetic energy is closely related to the dominant vortex prevailing inside the 180-deg sharp turn. For the first time, the measured flow characteristics account for the reported spanwise heat transfer distributions in the rotating channels, especially the high heat transfer enhancement on the leading wall in the turn. For both rotating and non-rotating cases, the direction and strength of the secondary flow with respect to the wall are the most important fluid dynamic factors affecting local heat transfer distributions inside a 180-deg sharp turn. The role of the turbulent kinetic energy in affecting the overall enhancement of heat transfer is well addressed.

LES of Turbulent Separated Flow and Heat Transfer in a Symmetric Expansion Plane Channel

2005 ◽  
Vol 127 (5) ◽  
pp. 865-871 ◽  
Author(s):  
Kazuaki Sugawara ◽  
Hiroyuki Yoshikawa ◽  
Terukazu Ota
Keyword(s):  
Heat Transfer ◽  
Finite Difference ◽  
Plane Channel ◽  
Separated Flow ◽  
Expansion Ratio ◽  
Vortical Flow ◽  
Flow And Heat Transfer ◽  
Finite Difference Equations ◽  
Separated And Reattached Flow ◽  
Fundamental Equations

The LES method was applied to analyze numerically an unsteady turbulent separated and reattached flow and heat transfer in a symmetric expansion plane channel of expansion ratio 2.0. The Smagorinsky model was used in the analysis and fundamental equations were discretized by means of the finite difference method, and their resulting finite difference equations were solved using the SMAC method. The calculations were conducted for Re=15,000. It is found that the present numerical results, in general, agree well with the previous experimental ones. The complicated vortical flow structures in the channel and their correlations with heat transfer characteristics are visualized through various fields of flow quantities.

scholarly journals Measurement of Unsteady Flow and Heat Transfer in a Linear Turbine Cascade

1992 ◽  
Author(s):  
X. Liu ◽  
W. Rodi
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Unsteady Flow ◽  
Boundary Layers ◽  
Suction Side ◽  
Turbine Cascade ◽  
Transfer Coefficients ◽  
Flow And Heat Transfer ◽  
Background Turbulence ◽  
Hot Film

A detailed experimental study has been conducted on the wake-induced unsteady flow and heat transfer in a linear turbine cascade. The unsteady wakes with passing frequencies in the range zero to 240 Hz were generated by moving cylinders on a squirrel cage device. The velocity fields in the blade-to-blade flow and in the boundary layers were measured with hot-wire anemometers, the surface pressures with a pressure transducer and the heat transfer coefficients with a glue-on hot film. The results were obtained in ensemble-averaged form so that periodic unsteady processes can be studied. Of particular interest was the transition of the boundary layer. The boundary layer remained laminar on the pressure side in all cases and in the case without wakes also on the suction side. On the latter, the wakes generated by the moving cylinders caused transition, and the beginning of transition moves forward as the cylinder-passing frequency increases. Unlike in the flat-plate study of Liu and Rodi (1991a) the instantaneous boundary layer state does not respond to the passing wakes and therefore does not vary with time. The heat transfer increases under increasing cylinder-passing frequency even in the regions with laminar boundary layers due to the increased background turbulence.

SIMULATION OF FLUID FLOW AND HEAT TRANSFER IN A PLANE CHANNEL USING THE LATTICE BOLTZMANN METHOD

2003 ◽  
Vol 17 (01n02) ◽  
pp. 183-187 ◽  
Author(s):  
G. H. TANG ◽  
W. Q. TAO ◽  
Y. L. HE
Keyword(s):  
Heat Transfer ◽  
Distribution Function ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Plane Channel ◽  
Parallel Plates ◽  
Thermal Boundary Conditions ◽  
Flow And Heat Transfer ◽  
Forced Convective Flow ◽  
Boltzmann Method

Forced convective flow and heat transfer between two parallel plates are studied using the lattice Boltzmann method (LBM) in this paper. Three kinds of thermal boundary conditions at the top and bottom plates are studied. The velocity field is simulated using density distribution function while a separate internal energy distribution function is introduced to simulate the temperature field. The results agree well with data from traditional finite volume method (FVM) and analytical solutions. The present work indicates that LBM may be developed as a promising method for predicting convective heat transfer because of its many inherent advantages.

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