Sakchai Uapipatanakul

Bio: Sakchai Uapipatanakul is an academic researcher. The author has contributed to research in topics: Dissipation & Open-channel flow. The author has an hindex of 1, co-authored 1 publications receiving 3 citations.

Development of computational methods for conjugate heat transfer analysis in complex industrial applications

Abstract: Conjugate heat transfer is a crucial issue in a number of turbulent engineering fluidflow applications, particularly in nuclear engineering and heat exchanger equipment.Temperature fluctuations in the near-wall turbulent fluid lead to similar fluctuationsin the temperature of the solid wall, and these fluctuations in the solid cause thermalstress in the material which may lead to fatigue and finally damage.In the present study, the Reynolds Average Navier-Stokes (RANS) modelling approachhas been adopted, with four equation k????2??? eddy viscosity based modelsemployed to account for the turbulence in the fluid region. Transport equations forthe mean temperature, temperature variance, ?2, and its dissipation rate, ??, have beensimultaneously solved across the solid region, with suitable matching conditions forthe thermal fields at the fluid/solid interface.The study has started by examining the case of fully developed channel flow withheat transfer through a thick wall, for which Tiselj et al. [2001b] provide DNS dataat a range of thermal activity ratios (essentially a ratio of the fluid and solid thermalmaterial properties). Initial simulations were performed with the existing Hanjali�cet al. [1996] four-equation model, extended across the solid region as described above.However, this model was found not to produce the correct sensitivity to thermal activityratio of the near wall ?2 values in the fluid, or the decay rate of ?2 across the solid wall. Therefore, a number of model refinements are proposed in order to improve predictionsin both fluid and solid regions over a range of thermal activity ratios. These refinementsare based on elements from a three-equation non-linear EVM designed to bring aboutbetter profiles of the variables k, ?, ?2 and ?? near the wall , and their inclusion is shownto produce a good matching with the DNS data of Tiselj et al. [2001b].Thereafter, a further, more complex test case has been investigated, namely an opposedwall jet flow, in which a hot wall jet flows vertically downward into an ascendingcold flow. As in the channel flow case, the thermal field is also solved across the solidwalls. The modified model results are compared with results from the Hanjali�c modeland LES and experimental data of Addad et al. [2004] and He et al. [2002] respectively.In this test case, the modified model presents generally good agreement with the LESand experimental data in the dynamic flow field, particularly the penetration point ofthe jet flow. In the thermal field, the modified model also shows improvements in the ?2predictions, particularly in the decay of the ?2 across the wall, which is consistent withthe behaviour found in the simple channel flow case. Although the modified model hasshown significant improvements in the conjugate heat transfer predictions, in some instancesit was difficult to obtain fully-converged steady state numerical results. Thusthe particular investigation with the inlet jet location shows non-convergence numericalresults in this steady state assumption. Thus, unsteady flow calculations have beenperformed for this case. These show large scale unsteadiness in the jet penetration area.In the dynamic field, the total rms values of the modelled and mean fluctuations showgood agreement with the LES data. In the thermal field calculation, a range of the flowconditions and solid material properties have been considered, and the predicted conjugateheat transfer predicted performance is broadly in line with the behaviour shownin the channel flow.

RANS Modelling for Temperature Variance in Conjugate Heat Transfer

Abstract: We predict how turbulence generated temperature fluctuations propagate from the fluid regions into the adjacent walls. Within the RANS approach this is achieved by extending the transport equations for temperature variance and its dissipation rate across the solid walls which bound the flow region. The results of recent DNS studies of conjugate heat transfer under fully developed conditions in straight channels have been used to develop and optimize the model. Simulations of 1D fully developed channel flow (friction Reynolds number 150, Prandtl numbers 0.71 and 7) with heated solid wall are carried out and compared with DNS data, using an existing four-equation model proposed by Craft et al.[4] as a starting point. The transport equations for the two thermal parameters, temperature variance and its dissipation rate, are optimized by focusing on the decay of these two parameters in the solid region, using boundary values at the interface between the solid and fluid regions provided by DNS. Then a physically consistent and numerically stable set of interface conditions are developed to account for the jump in the value of temperature variance dissipation rate across the solid-fluid interface, caused by the different material thermal properties. Subsequent conjugate heat transfer simulations show that the proposed model is able to predict the correct distribution of the temperature variance within both the fluid and solid regions, for the entire range of thermal diffusivity and conductivity ratios between the fluid and solid regions and also for both fluid Prandtl numbers.

RANS Model development on temperature variance in conjugate heat transfer

Abstract: In this study, a RANS model of turbulent conjugate heat transfer has been developed, which is applicable across a range of different combination of fluid and solid thermal properties. This is achie...

Application of the Finite-Volume Method to Fluid-Structure Interaction Analysis

Abstract: This paper describes the numerical simulation of steady flow through severely stenosed tubes and the development of a fully coupled fluid-solid solver, capable of predicting the effects of fluid pressure and wall shear stress on the elastic tube wall. This particular type of interaction occurs commonly in physiological flows. Whilst geometrically simple, even with a rigid wall this type of flow exhibits many complex phenomena such as re-circulation and transition to turbulence, both of which make numerical simulation difficult. Initially, flow simulations are reported for a rigid walled tube over a range of physiologically relevant flow rates. Laminar simulations were only successful for Reynolds numbers of less than 300; deviation from the experimental data occurred at the experimentally observed point of transition. Computations using a low-Reynolds-number turbulence model proved successful for Reynolds numbers greater than 1500, with results being in good agreement with experimental data. Following these rigid-wall CFD simulations, a finite-volume based method for solving solid body stress analysis problems has been developed, and the results of a validation exercise show good agreement with analytical solutions. This solid body solver has then been coupled to the CFD code to allow fully coupled fluid-structure interaction (FSI) analyses of flow through a compliant walled stenosis to be performed. Initial results from such coupled cases show a reasonably accurate response of the wall deformation to the flow rate