Mitsunobu Akiyama

Calculation of turbulent heat flux distributions in a square duct with one roughened wall by means of algebraic heat flux models

Abstract Calculations have been performed for fully developed turbulent flow and heat transfer in a square duct with one roughened wall. This paper focuses on the application of two algebraic models of the turbulent heat flux transport equation to predict turbulent heat flux component behavior. The convection and diffusion terms in this transport equation are modeled in a manner similar to Rodis approximation for corresponding terms in the Reynolds stress transport equations. The pressure–temperature gradient term is simulated by means of two models: one a composite based on the “slow” and “rapid” interaction models proposed by Lumley and Launder (LL), respectively, and the other, the model proposed by Jones and Musonge (JM). Both the LL and JM models lead to predicted mean temperature distributions in the duct cross plane that are in relatively good agreement with experimentally measured distributions. The LL model, however, yields predicted distributions that agree better with experiment near both the smooth and roughened walls of the duct. Calculated turbulent heat flux component distributions in the cross plane show that both the LL and JM models predict experimentally observed features in the flow, with the LL model providing the best overall accuracy.

Analytical Study of Volumetric Scroll Pump for Liquid Hydrogen Circulating System

The paper presents analytical results of suction process of a volumetric scroll pump, which will be developed for circulating liquid hydrogen in a cold moderator system. The multi-block grid generation approach has been applied to generate a moving boundaries computational model. The finer mesh patterns have been generated in the near-wall regions. The Low-Reynolds number k-ε turbulence model has been solved for predicting Reynolds stresses and turbulent scalar fluxes. The analysis has been carried out under liquid hydrogen flow conditions. The heat transfer effect is neglected to simplify the study. The analytical results show that at the end of suction process the relative pressures increase significantly in a pocket while decrease continuously in another pocket. This phenomenon might damage scroll pump components if the high-pressure side is too high and/or the low-pressure side is too low until the cavitations occur. Therefore, the pocket should open to the discharge chamber before it closes and separates from the suction chamber in order to prevent the cavitations and extremely high-pressure regions.

Prediction of Flow Patterns and Pressure Distributions in Suction Process of Volumetric Scroll Pump

Prediction of Flow Patterns and Pressure Distributions in Suction Process of Volumetric Scroll Pump Phichai KRITMAITREE a , Mitsunobu AKIYAMA a , Ryutaro HINO b , Masanori KAMINAGA b & Atsuhiko TERADA b a Mechanical Engineering Department , Utsunomiya University , Ishii-cho , Utsunomiyashi , Tochigi , 321-0912 b System Engineering Group, Tokai Research Establishment , Japan Atomic Energy Research Institute , Shirakata , Tokai-mura , Naka-gun , Ibaraki , 319-1195 Published online: 07 Feb 2012.

Collision Analysis of Quasi-Rigid Balls by High-Speed Camera

Trajectories of the billiard balls have long been assumed to behave as the collision of mass points. As a matter of fact, the beginners can enjoy the games with this simple assumption. On the contrary, the professional players know the differences from the theory by their plentiful experiences and adjust them by intuitions. In order to investigate the mechanisms of the differences from the theory and to quantify them under various circumstances, the authors of this study have visualized the movements of the balls by the high-speed camera and have investigated the trajectories quantitatively by using the digital image processing techniques. As a result, velocity, momentum and kinetic energy before and after the collisions between ball and rubber cushion and between ball and ball have been measured. Moreover, the evidence of “throw”, which is one of the typical discrepancies from the theory, has been shown quantitatively.

Numerical Analysis of Turbulent Heat Transfer in a Square Duct with One Rough Wall by Algebraic Turbulent Heat Flux Models.

A numerical analysis has been performed for fully developed turbulent flow and heat transfer in a rectangular duct with smooth and rough walls by using algebraic Reynolds stress and turbulent heat flux models. The wall functions and the universal law of the wall, which are used as the boundary conditions of turbulent energy and dissipation, apply in the present analysis instead of taking shape of roughness element into account. Therefore, the roughness enters through the log law relating the velocity at the first grid point away from the wall with the friction velocity. In this numerical analysis, two kinds of turbulent heat flux models, i. e. Lumley-Launder model and Jones-Musonge model, are examined to compare the contour distributions of turbulent heat fluxes in three dimensions which have been measured in detail. In numerical analysis, convection and diffusion terms for the transport equation of turbulent heat flux are modelled as an algebraic turbulent heat flux model. From the comparison calculated results with the experimental data, it is found that two models can predict the mean temparature distributions which are distorted near the smooth wall located opposite to rough wall side. On top of that, Lumley-Launder model is able to better realize mean temperature near smooth and rough walls than Jones-Musonge model. As for comparison of the turbulent heat flux, calculated results suggest that two models predict characteristic features while two models have tendency to overestimate the experimental values.

Three-Dimensional Measurement of Air Velocity by High-Speed Cameras and DP Matching Method

Dynamic programming matching technique, which is used for the voice recognition, has been adopted to the time line images obtained by the spark tracing method for the high speed air flow. As the high voltage sparks between two electrodes trace the air flow very well, we can measure the two or three-dimensional air velocities, if we can quantify the displacement and the time interval between sparks. With the dynamic programming matching technique, the characteristics of the two consecutive spark lines are nicely corresponded and thus the three-dimensional displacement between sparks are quantified. Presently, the high speed air jet has been measured with this technique.

Numerical Analysis of Secondary Flow for Viscoelastic Fluid Through Elliptical Duct.

The flow behavior of viscoelastic non-Newtonian fluid in circular and non-circular ducts is of special engineering interest. Therefore a numerical analysis has been performed for viscoelastic non-Newtonian fluid in elliptical duct. Special attention is paid for the generation of secondary flow for laminar flow by using two kinds of constitutive equation, i.e., Maxwell and Reiner-Rivlin models. As for Maxwell model, body force caused by the elastic stress is approximated by linear source term. In calculation, viscosity was represented by adopting power-law fluid and boundary-fitted coordinate system was introduced as the method of coordinate transformation. The calculated results of two models show the secondary flow in elliptical duct as the same as theoretically analyzed by Green and Rivlin. Adding to the prediction of secondary flow, the generation mechanism of secondary flow has been argued by evaluating the production terms of the transport equation for streamwise vorticity. As a result of this examination, it was found that the term of viscous diffusion and the term containing second normal stress difference played an important role in producing the secondary flow near the wall. At the same time, it is interested phenomenon that the circular direction of secondary flow for viscoelastic fluid is opposite sigh to that of secondary flow for Newtonian turbulent flow. As its cause, the present study clarified that the term containing second normal stress difference of viscoelastic fluid is the same type equation for that of turbulence, while the sign of its term for viscoelastic fluid is opposite to that for turbulent flow.

Assessment of Volume Traking Algorithms in a Three-Diemensional Flow Field Dominated by Surface Tension.

In this study, numerical analysis has been performed to clarify the assessment of volume tracking algorithms in a three-dimensional flow field dominated by surface tension. The FLAIR method has been extended to three-dimensional problems in this study. The distinct feature of FLAIR developed in two-dimension is that the slope of line segment is estimated based only on two neighboring volume fractions. This feature is also adopted in the three-dimensional FLAIR method proposed in this study, even if the three-dimensional slope of interface is neglected. This three-dimensional FLAIR is applied to a non-straining flow field and a surface tension dominated flow field. The results are compared with those of the donor-acceptor method, the SURFER method and the CIP method with digitization. Consequently, it has been found that the precision of translation of interface is much more improved by the use of the CIP method with digitization and the three-dimensional FLAIR method than that of the other methods. However, the CIP method with digitization will produce an uneven interface.

Numerical Analysis of Turbulent Flow Developing in Longitudinally Finned Tubes.

A numerical analysis has been performed for turbulent flow developing in longitudinally finned tubes. Three tube geometries were calculated : two 8-finned tubes (fin hight to radius ratios of 0.333 and 0.167) and one 16-finned tube (fin height to radius ratio of 0.167). In calculations, an algebraic Reynolds stress model was adopted in order to predict precisely the secondary flow of the second kind induced by anisotropic turbulence and boundary-fitted coordinate system was introduced as the method of coordinate transformation. Mean velocities in axial, radial and circumferencial directions, pressure drop in tubues and primary shear stress distribution are compared with the experimental data. As a result of this analysis, it was found that the present method could predict well the streamwise mean-velocity. In the case of 8-finned tube of tin height-to-radius ratio 0.333, two secondary flow cells which were measured in experiment, were reproduced by the present turublent model although a small intensity of secondary flow were observed compared with the experiment. Moreover, numerical results suggest that these two secondary flow cells disapper in 8-finned tube of tin height-to-radius ratio 0.167 and the secondary flow has a influence on the wall shear stress distribution. The calculated results also show that the turbulence in the interfin region is greatly reduced as well as the experiment.

Numerical Analysis of Turbulent Flow of Non-Newtonian Fluids in Eccentric Annular Passage

A numerical analysis has been performed for developing turbulent flow of non-Newtonian fluid in eccentric annular passage. Several calculations have been carried out to examine the drag reduction with decreasing power index of power-law fluids and the reduction of skin friction factor with increasing eccentricity defined by the distance between the centers of the inner and outer pipes for Newtonian fluid. In numerical analysis, the power law model for non-Newtonian fluid and an algebraic Reynolds stress model for turbulent flow were adopted in order to predict precisely non-Newtonian flow behaviour. Boundary-fitted coordinate system was introduced as the method of coordinate transformation. The numerical results are compared with the experimental data involving stramwise velocity and fluctuating velocities in axial, radial and tangential directions. As a result of comparison with the experiment, it was found that the present method could predict well the streamwise meam-velocity in both fluids and reproduce the secondary flow of the second kind generated by anisotoropic turbulence. As for the comparison of fluctuating velocities, the agreement with experimental data is more satisfied for Newtonian fluid than for non-Newtonian fluid. The calculated results also suggest that the drag reduction with polymer solution is realized by the present method as well as the experiment and the phenomenon of decaying fluctuating velocity with decreasing power index is predicted.