Effect Of Wall Geometry Research Articles

Flow and heat transfer characteristics in a channel having furrowed wall based on sinusoidal wave

The effect of wall geometry on the flow and heat transfer in a channel with one lower furrowed and an upper flat wall kept at a uniform temperature is investigated by large eddy simulation. Three channels, one with sinusoidal wavy surface having the ratio (amplitude to wavelength) α/λ=0.05 and the other two with furrowed surface derived from the sinusoidal curve, are considered. The numerical results show that the streamwise vortices center is located near the lower wall and vary along the streamwise on various furrow surfaces. The furrow geometry increases the pressure drag and decreases the friction drag of the furrowed surface compared with that of the smooth surface; consequently, the total drag is increased for the augment of pressure drag. As expected, the heat transfer performance has been improved. Finally, a thermal performance factor is defined to evaluate the performance of the furrowed wall.

Determination of hot spots on a heated wavy wall in channel flow

The present study deals with the effects of wall geometry on the fluid flow and heat transfer in a channel with a wavy wall heated with constant heat dissipation. The waviness is characterized by wave amplitude and period. A detailed parametric numerical investigation of the effect of waviness on the local heat transfer parameters is performed for different turbulent flow conditions and compared with the literature.The effect of flow and geometry parameters is assessed quantitatively. Generalization is done based on the Reynolds number, ReA, which uses doubled wave amplitude, or height, A=2a, as the characteristic length, and on the geometry parameter, A/λ, which essentially is the amplitude-to-wavelength ratio. A dimensionless location of the hottest spot on the wavy wall is shown to be dependent on these two dimensionless parameters. A correlation which encompasses the hottest spot locations for all the cases studied in the work is suggested.In order to obtain generalization for the hottest spot temperature, the Nusselt number is introduced based on the constant (uniform) heat flux and variable temperature difference, with wave amplitude as the characteristic length. It is shown that, for all cases studied herein, the hottest temperature is represented as NuA,min(ReA,A/λ). Accordingly, a correlation for the minimum Nusselt number is suggested. A further generalization for the hottest spot temperature is attempted for the conjugate problem with a conducting wall. It includes wall-to-fluid thermal conductivity ratio, ks/kl, as the additional dimensionless parameter which determines the Nusselt number.

Numerical and experimental study on effect of wall geometry on wall impingement process of hollow-cone fuel spray under various ambient conditions

The spray–wall impingement process in gasoline direct injection (GDI) engines, which is caused by the interaction among spray, wall and air to move the air–fuel mixture near the spark plug, directly influences the engine performance and emissions. Therefore, a detailed understanding of this process is very important in designing an injection system and controlling a strategy of GDI engines. The purpose of this study is to understand the spray–wall impingement characteristics for more efficient designing of the injection system in GDI engines and to supply the fundamental data under engine operation conditions. The wall impingement processes of hollow-cone fuel spray according to ambient gas conditions and wall geometry are calculated by validated spray models. The calculated results were compared with the experimental results obtained by the laser-induced exciplex fluorescence (LIEF) technique. It was found that the spray and vortex cloud at the high ambient pressure were distributed at inner area of cavity and the more fuel film mass observed at this condition. The fuel film mass decreased with the increase of ambient temperature, while the fuel film mass increased at high cavity angles.

Optimization of rib-roughened annular gas-coolant channels

The present study deals with the effects of wall geometry on the fluid flow and heat transfer in an annulus. Rectangular-rib structural wall roughness on the inner wall is considered. This roughness is characterized by rib height, width and pitch. A detailed parametric investigation of the effect of rib width-to-height ratio on the friction coefficient is performed for different rib pitches. This ratio varies from 0.125 to 6.0. Various rib pitches are considered, from those corresponding to a smooth wall, and up to the pitch-to-rib-height ratio of 16. Examples of various rib heights are also shown. The hydraulic diameter and the flow Reynolds number serve as additional parameters. Numerical simulations are performed using a modified k– ɛ turbulence model, which makes possible the prediction of flow separation, reattachment and adverse pressure gradients. The model is validated by comparing its results with experimental and numerical results for overall and local flow parameters reported in the literature. The results of the present study indicate that for the given hydraulic diameter of the annulus and flow Reynolds number, the pitch that corresponds to maximal flow resistance depends on the rib width-to-height ratio. It appears that when the width-to-height ratio decreases, this optimal pitch approaches an asymptotic value. On the other hand, the optimum rib distance-to-height ratio remains almost constant. These findings are discussed in context of the available literature. Generalization of the results is attempted through the use of dimensionless groups based on the flow and geometrical parameters of the systems. A correlation for the friction factor is suggested.

Effect of wall geometry on the behaviour of reinforced soil walls

The effect of geometric parameters such as reinforcement length, number of layers of reinforcement, distribution of reinforcement and wall height on the forces developed in the reinforcement is examined. It is shown that the forces developed are largely independent of reinforcement length for reinforcement to wall height ratios equal to or greater than 0·7. For truncated reinforcement schemes with a ratio of less than 0·7, the forces in the reinforcement increase as the length of the reinforcement decreases. The number of layers of reinforcement was not found to significantly affect the total force required for equilibrium provided the reinforcement stiffness density was the same. The analysis provides theoretical support for the common practice of using truncated reinforcement with equal vertical spacing and length equal to 70% (or greater) of the wall height.