The aim of this paper is to study flow regime changes of Newtonian fluid flow in an open Venturi channel. The simulations are based on the volume of fluid method with interface tracking. ANSYS Fluent 16.2 (commercial code) is used as the simulation tool. The simulation results are validated with experimental results. The experiments were conducted in an open Venturi channel with water at atmospheric condition. The inlet water flow rate was 400 kg/min. The flow depth was measured by using ultrasonic level sensors. Both experiment and simulation were done for the channel inclination angles 0 , À0.7 , and À1.5. The agreement between computed and experimental results is satisfactory. At horizontal condition, flow in the channel is supercritical until contraction and subcritical after the contraction. There is a hydraulic jump separating the supercritical and subcritical flow. The position of the hydraulic jump oscillates within a region of about 100 mm. Hydraulic jumps coming from the contraction walls to the upstream flow are the main reasons for the conversion of supercritical flow into subcritical flow. An ''oblique jump'' can be seen where there is a supercritical flow in the contraction. There is a triple point in this oblique jump: the triple point consists of two hydraulic jumps coming from the contraction walls and the resultant wave. The highest flow depth and the lowest velocity in the triple point are found at the oblique jump.

The one-dimensional shallow water equations were modified for a Venturi contraction and expansion in a rectangular open channel to achieve more accurate results than with the conventional one-dimensional shallow water equations. The wall-reflection pressure-force coming from the contraction and the expansion walls was added as a new term into the conventional shallow water equations. In the contraction region, the wall-reflection pressure-force acts opposite to the flow direction; in the expansion region, it acts with the flow direction. The total variation diminishing scheme and the explicit Runge-Kutta fourth-order method were used for solving the modified shallow water equations. The wallreflection pressure-force effect was counted in the pure advection term, and it was considered for the calculations in each discretized cell face. The conventional shallow water equations produced an artificial flux due to the bottom width variation in the contraction and expansion regions. The modified shallow water equations can be used for both prismatic and nonprismatic channels. When applied to a prismatic channel, the equations become the conventional shallow water equations. The other advantage of the modified shallow water equations is their simplicity. The simulated results were validated with experimental results and three-dimensional computational fluid dynamics result. The modified shallow water equations well matched the experimental results in both unsteady and steady state.

Open Venturi channel flow measurement could be a cheap method to be used in drill bit pressure control. The main objective of this study is to identify the factors related with the flow depth in an open Venturi channel. A commercial computational fluid dynamics tool was used for the simulations. The simulation results were validated with the previous related experimental results. The agreement between simulation and experimental data was satisfactory. The open Venturi channel at a horizontal angle gave a higher flow depth before the contraction region compared to its negative angles (downward). When the channel inclination angle was reduced, flow velocity increased and flow depth reduced. Likewise, flow became supercritical and created a hydraulic jump. The wall roughness played a significant role with the starting position of the hydraulic jump. This was due to the energy loss between wall and fluid. There is an energy loss in a hydraulic jump, when the supercritical flow transition into the subcritical flow. Large eddies were generated in a hydraulic jump. Flow depths difference between supercritical and subcritical is a factor to generate the large eddies. Fine meshes gave sharp interfaces, which was similar to what is seen in reality. The difference turbulence models: standard k-ε model, k-ω model, k-ε RNG model and k-ε realizable model gave almost the same flow depths.

The Euler-Granular approach was used to predict pneumatic conveying characteristics of vertically upward dilute phase flow. Three-dimensional computational fluid dynamics simulations were carried out for 8 m long and 30.5 mm diameter circular pipe. The density of conveyed materials was 1020 kgm-3. Simulations for different particle diameters: 200 µm, 500 µm and 3 mm were performed. The air velocities ranged from 7 to 16 ms-1 and solid to air mass flow ratios ranged from 1.2 to 3.6. The main objective of this study was to analyse the sensitivity of specularity coefficient in Johnson and Jackson particle-wall boundary conditions on conveying characteristics. It was found that there is a significant sensitivity of certain ranges of specularity coefficients on pressure drop, air and particle velocities and solid distribution in pipe cross section. Among the tested range of the specularity coefficient values, some values are recommended for different particle sizes by comparing the predicted results with experimental data from existing literature. Moreover, it was also found that the coefficient of restitution for particle-wall collisions which counts the momentum loss by the walls in normal direction has less sensitivity on the results compared to that of specularity coefficient which counts the momentum loss by the walls in tangential direction.

The two-phase drift flux model is extensively used in multiphase flow applications. In this study, we focus on possible numerical schemes for solving the drift flux model. Due to the complexity of the primitive equations and empirical parameters, it is challenging to achieve stability of the numerical scheme used for the drift flux model. The high resolution second order central scheme, the high resolution second order central-upwind scheme, and the high resolution third order and fifth order weighted essentially non-oscillatory schemes (WENO) were successfully implemented for the drift flux model. The schemes were tested with the shock tube discontinuity problem. The central-upwind-WENO scheme was developed and applied to the drift flux model. In the central-upwind-WENO scheme, the cell interface values were taken from the WENO reconstruction, and the monotone flux is calculated from the central-upwind flux. The central-upwind-WENO scheme can achieve higher order accuracy than the central-upwind scheme by using the same stencils which are used for the central-upwind scheme. The central-upwind-WENO scheme gives more accurate results than the central scheme, central-upwind scheme and the WENO scheme. Especially at the rarefaction and shock wave fronts, the central-upwind-WENO scheme gives sharper gradients compared to the other schemes. Instead of a limiter function, the central-upwind-WENO scheme uses a smoothness indicator. All the schemes used in the study are suitable for two-phase drift flux model simulation.