In this study, two-dimensional pulsating unsteady flow of nanofluid through a rectangular channel with isothermal walls is investigated numerically. The finite volume approach with a staggered grid arrangement is employed to discretize the governing momentum and energy equations. The set of resultant algebraic equations is solved simultaneously using SIMPLE algorithm to obtain the velocity and pressure distribution within the channel. The results are obtained for different pulse parameters, which are Strouhal number (frequency of pulsation), Amplitude of pulsation, Reynolds number and volume fraction of nanoparticles. The results show that increasing the amplitude of pulsation has no effect on cycle period of pulsation, while it can raise the Nusselt number. The analysis also reveals that increasing the Strouhal number reduces the cycle period of pulsation significantly, while its effect on the rate of heat transfer is not more appreciable. Furthermore, it is found that the heat transfer increases, as the volume fraction of nanoparticles and Reynolds number increase. It can also be seen that the maximum value of relative Nusselt number for silver nanoparticles is more than other studied nanoparticles.

This paper presents the results of an experimental and numerical study of fully developed flow in a straight rectangular open channel over rough beds. Conical ribs were placed on the flume bottom to simulate different bed roughness conditions. Acoustic Doppler Velocimetry (ADV) measurements were made to obtain the velocity components profiles as well as the Reynolds stress profiles, at various locations. The experimental results are validated by simulations using an algebraic stress model. These investigations could be useful for researches in the field of sediment transport, bank protection, etc.

Study in mixing processes for the management of water quality of rivers is important and one of the environmental concerns. The substrates, such as dunes, are effective in control of transport, production of turbulence and flow resistance in rivers, canals and wetlands It is therefore essential that study is done in this subject. The objective of this study is to investigate the transversal mixing coefficient of dunes. For this purpose, measurements carried out on the fifth to the ninth of dunes in a series of ten dune sand of the synthetic twodimensional.The experiments carried out in a laboratory channel with dimensions of length, width and depth, 20, 0.6 and 0.6 respectively. The dunes had a wave-length of one meter, height 0.8 meters, downstream side slopes 28 degrees and width equal to the channel width. The average diameter of sand dunes used was 14 mm.To evaluate the effect of the delicately ratio on lateral mixing coefficients, two different depths were used. The results showed that dune plays an important role in increasing the lateral mixing coefficient so that in this case this rate was 2.36 times the flat bed. Complete mixing length in the channel bed dunes was 11 meters to the amount indicated on the flat bed of a third. This parameter showed a decrease with increasing depth over the dunes. The tests indicate that the self-purification power of the river on the dunes, comparing to a flat bed, with increasing water depth above of the dunes, increases.

In this study, two-dimensional pulsating unsteady flow of nanofluid through a rectangular channel with isothermal walls is investigated numerically. The set of resultant algebraic equations is solved simultaneously using SIMPLE algorithm to obtain the velocity and pressure distribution within the channel. The effects of several parameters, such as volume fraction of different nanoparticles, Reynolds number, and the amplitude and frequency of pulsation flow, on the rate of heat transfer and pressure drop are examined. The results show that the heat transfer enhancement on the target surface obtained by the flow pulsation highly depends on pulsating velocity. It can also be seen that total Nusselt number increases significantly due to increase in amplitude of pulsation and volume fraction of nanoparticles. Analysis also reveals that pressure drop for the alumina nanoparticles is much greater than that of the base fluid.

Introduction: Sediment transport is one of the most basic and important characteristics in river hydraulics and bed morphology. The prediction of sediment transport path in rivers and also cannels is absolutely complicated, and mostly conducted with semi-empirical methods. In such cases, the Lagrangian method is essential for exploring the physics of individual sediment particles. The investigation of the flow pattern in the compound open-channel originated in 1960s and followed by the exploration of turbulence structures of overbank flows. However, studies on the characteristics and processes of sediment transport in the compound channels are rarely conducted. For completion this gap, in this experimental study, the rolling and sliding motions of individual bed particle in the floodplain of a rectangular compound open-channel have been experimentally investigated. Specifically, the mechanical parameters of particle motions such as velocity and acceleration are investigated. In this regard, different statistical distributions, especially Gaussian or normal distribution, are employed to introduce the properties of bed sediment motions in the floodplain. Methodology: The experiments were conducted in the hydraulic laboratory of Tarbiat Modarres University in a straight open channel with length of 10 m, width of 1 m and height of 0. 7 m (Fig. 1). The laboratory flume is a wide rectangular channel with a compound section (Fig. 2), where the side wall and bottom of the channel are made of glass. The main channel is 0. 4 m wide and the floodplain is 0. 6 m wide. To control the water depth, an adjustable weir was used at the end of channel. The discharge at the inlet of the channel was controlled using a regulating valve downstream of pump and measured by an electromagnetic flow-meter. The hydraulic conditions of the experiments are summarized in Table 1. According to the calculations, the Reynolds and Froude numbers are respectively 28000 and 0. 34. Therefore, the flow in the compound channel of the present study is turbulent and subcritical. The flow depths in the floodplain and main channel are 5 and 20 cm, respectively. To capture high quality images from bed particle motions in short intervals, a camera with the speed of 24 frames per second and FullHD resolution was used (Fig. 3). To improve the quality of the images, the floodplain and main channel bottoms were coated with black color in the measurement zone. Moreover, for detection of the particle trajectories, the measurement zone was regularly meshed by the perpendicular lines with the distance of 10 cm. Several projectors were applied at different angles for illumination of the measuring plane. The spherical bed particle characteristics of the present study are mentioned in Table 2. Particle tracking were conducted at the distances of 5, 20, 40, and 50 cm from the floodplain side wall (Fig. 4), and repeated about 20 times for each one. Results and discussion: Chi-Squared test were used to determine the appropriate distribution to describe the longitudinal and transversal velocity and acceleration of individual particles (Fig. 5). Also, skewness and kurtosis of the data are employed to investigate the fitness of velocity and acceleration data to the normal distribution (Eqs. 2 and 3). In the case of sediment release at 20 cm from the floodplain side wall, the skewness values for the particle longitudinal and transversal velocities are always close to zero and their kurtosis values are close to 3, . This indicates that the particle longitudinal and transversal velocities follow the normal distribution. However, kurtosis of longitudinal acceleration diverges from 3, and consequently, it does not follow normal distribution (Table 3). The averaged longitudinal and transversal velocities of the sediment particles increase, approaching to the interaction zone (Fig. 6). Also, the standard deviation of longitudinal and transversal velocity and acceleration values increase with the increase of distance from the floodplain side wall (Fig. 7 and 8). Kurtosis of streamwise and spanwise velocity and acceleration of sediment particles increase far from floodplain side wall (Fig. 9), duo to the uniformity of particle motions in the interaction zone. The linear relationship between the average particle velocity and flow shear velocity indicates that there is a good agreement between the results of the present study and previous researches. Conclusion: The results of this study show that the sreamwise and lateral velocity and spanwise acceleration histograms of spherical particles in the floodplain far from the interaction zone, could be fitted to the normal distribution. While the kurtosis of histograms increases considerably, approaching to the junction. The histogram of streamwise acceleration does not fitted by the normal distribution. The histogram kurtosis of velocity and acceleration is enhanced approaching the interaction zone.

The precise prediction of shear stress in open channel is important in many engineering issues such as designing of sustainable channels, calculation of energy losses, and sedimentation in channels. In flood duration, due to difference in depth of flow between the main channel and the flood plains surrounding the flow, the flow velocity is also different, and subsequently the stress and distribution of stress significantly changes. In this paper, it has been shown the performance of the Ansys Fluent three-dimensional numerical model in simulating various hydraulic parameters for a rectangular compound channel with smooth and rough bed and wall. Comparison of shear stress values showed that with decreasing depth in flood plains, the amount and percentage of shear stress in flood walls, and in main channel increased and decreased respectively, and also it was shown that with increasing roughness, shear stress increased. Results also indicated that with increasing flow rate, the power flow increased and velocity and vortices were formed at the intersection of flood plains and main channels. The results of this research can play a role in designing of sustainable channels, especially at the intersection of the main channel and flood walls.

The coolant fluid inside the cooling channels may experience flow regime change and heat transfer deterioration. Heating methane at super-critical pressure results in a higher than pseudo-critical temperature and pseudo-phase change happens. Furthermore, in critical conditions, there is the possibility of heat transfer deterioration at high heat fluxes and low mass fluxes. In these areas, heat transfer from the wall to the fluid is disturbed due to the decrement in the heat transfer coefficient. Also, the wall temperature increases and there is the melting possibility of the engine wall. As a result, the study of this phenomenon is important for the thermal analysis of cryogenic methane for cooling applications. In the present article, a three-dimensional solver is developed for the simulation of the conjugate heat transfer inside a rectangular channel with trans-critical methane coolant. A finite volume scheme is utilized for the discretization of the governing equations. An iterative solution method based on the SIMPLEC algorithm is used to solve the equations. The solver is developed based on the thermodynamic and transport property relations corresponding to the coolant flow conditions in the trans-critical regime. The parametric study of the heat transfer deterioration phenomena is conducted utilizing the conjugate heat transfer simulations results of methane inside the MTP channel for heat transfer rate, inlet pressure and temperature, inlet mass flux, and different surface roughness. Further, a few relations are derived for predicting the onset of methane heat transfer deterioration along the rectangular cooling channel in a range of pressure from 6 MPa to 20 MPa. The relative error of derived relations with numerical data is less than 1 percent. Finally, some methods for controlling the heat transfer deterioration phenomena have been presented.

In the present study, the conjugate heat transfer in a rectangular cooling channel is numerically simulated in supercritical pressure conditions. The compressible methane flow is considered as a working fluid. A finite volume scheme is utilized for the discretization of the governing equations on a collocated grid. Moreover, the central differencing scheme is employed for the discretization of the diffusion fluxes and density approximation on the control volume boundaries. Upwind and hybrid schemes are used for the density correlation approximation and the convective fluxes discretization on the control volume surfaces, respectively. An iterative solution method based on the SIMPLEC (Semi-Implicit Method for Pressure Linked Equations-Consistent) algorithm is adopted to solve the equations. The solver is developed based on the thermodynamic and transport property relations corresponding to the coolant flow conditions in the transcritical regime. The solver is validated with the experimental data of the MTP test, and the thermal behavior of methane inside the rectangular cooling channel is investigated. Moreover, a relation is derived to calculate the pseudo-critical temperature of methane according to pressure. The relative error of this relation with NIST data is less than 0. 5 percent, and it operates in a range of pressure from 4. 6 MPa to 30 MPa. Furthermore, the Nusselt relations presented for coolant flow with supercritical pressures are studied and corrected for the methane coolant in supercritical pressure conditions in 3D rectangular cooling channels. The relative error of modified Nusselt relations with numerical data is less than 1. 0 percent.

The fracturing bridge due to scour of foundation (includes bed and abutment), reveals the necessity of study for scour predict and the protected methods. Generally, the methods of scour reduction include: placing foundation at the lower level of erosion pit depth, rasing bed resistance and decressing erosion power factors (decreasing downflow and horseshoe vortex). Utilizing a spreadsheat around abutment called collar is one of the methods of power decrease. The collar decreases the power of downflow and horseshoes vortex around the abutment further it decreases the depth of scour decrease. In this research a collar of two times than the abutment width exposed to a discharge of 20 and 25 lit/s. The operation of collar in 3 different depths (on the bed, at 2cm above bed and at 4cm above bed) was studied in the scour conditions of clear water and was compared with abutment without collar. the research indicate that collar decreases scour and it showed better operation above the bed.as a maximum percentage decrease of scour with a discharge of 20 and 25 lit/s is 94% and 93% respectively.

Lateral dead zone Studies are very important because the flow turbulence specifications in this situation are not fully known yet. Also in a series of lateral dead zones, their placement, number and size have different effect on the flow pattern. In this study, an attempt was made to determine the ability of STAR-CCM + in three-dimensional simulating of flow in series of rectangular ateral dead zone. For this purpose, the results of an experimental model was used. STAR-CCM+ was calibrated to determine the most suitable turbulence models and in order to validate, resuts, the data obtained from transverse fluctuations along the width of channel was used. data . The results showed that accelerating the flow in the main channel more flow separation and increase the flow velocity gradient near the upstream corner of dead zone. With the entry into dead zone, average flow velocity reduces and low-velocity zone appears as a circular area. Analyzing the flow pattern showed that in simulation of turbulence distribution RANS 2-end order model has a better efficiency in comparison with RANS 1-end order model. Finally the LES model showed the highest efficiency in the flow simulation.