Iraj Mirzaee

A numerical heat transfer study of slot jet impinging on an inclined plate

Purpose – This paper seeks to conduct a numerical study to investigate heat transfer in turbulent, unconfined, submerged, and inclined impinging jet discharged from a slot nozzle, utilising finite volume code FLUENT.Design/methodology/approach – Two re‐normalisation group k‐e and the basic Reynolds stress models by using enhanced wall treatment for near wall turbulent modelling were applied and the local Nusselt numbers were compared with experiments. The enhanced wall treatment solves the fully turbulent region and viscous sublayer by considering a single blended function of both layers.Findings – In inclined impinging jet by movement of stagnation point to the uphill side of the impinging plate, the location of the maximum Nusselt number moves to the uphill side of the plate. However, this movement increases by increasing of H/D and by decreasing of Reynolds number and inclination angle. For a flat plate impinging jet, the results were found to be less than 8 per cent different and for inclined impingin...

An immersed boundary–lattice Boltzmann approach to study the dynamics of elastic membranes in viscous shear flows

Abstract A combined immersed boundary–lattice Boltzmann approach is used to simulate the dynamics of elastic membrane immersed in a viscous incompressible flow. The lattice Boltzmann method is utilized to solve the flow field on a regular Eulerian grid, while the immersed boundary method is employed to incorporate the fluid–membrane interaction with a Lagrangian representation of the deformable immersed boundary. The distinct feature of the method used here is to employ the combination of simple Peskins IBM and standard LBM. In order to obtain more accurate and truthful solutions, however, a non-uniform distribution of Lagrangian points and a modified Dirac delta function are used. Two test cases are presented. In the first case, we consider a vesicle suspended in a simple shear flow commonly known as tank-treading motion. The computed results were compared with experiments, which showed reasonably good agreement. For the second test case, we consider individual healthy (soft) and sick (stiff) RBCs suspended in a shear flow. The simulation results demonstrated that elastic deformation plays an important role in overall RBC motions characterized as tank-treading and tumbling motions, in which the natural state of the elastic membrane is an essential consideration. In addition, the results confirm that the combination of the immersed boundary and lattice Boltzmann methods permits the simulation of the complex biological phenomena.

A Mathematical-Numerical Model to Calculate Load Distribution, Contact Stiffness and Transmission Error in Involute Spur Gears

This paper firstly presents a mathematical model in order to calculate the load distribution, single contact stiffness and meshing stiffness as well as transmission error. in this way, there is no need to use finite element like methods and also the calculation time is dramatically reduced. Presented method is based on definition of a statically undetermined problem that is formulated using energy method. Some assumptions considered to convert this problem to a statically determined problem and get the mathematical models. Then a numerical method is employed in order to solve the mathematical model using a double iteration flowchart to close the problem. This model is flexible to adapt for any modification in spur gear profile geometry. Finally, this model is verified using previous works that have been utilized finite element and experimental model.Copyright

Design of water distribution networks using accelerated momentum particle swarm optimisation technique

Optimisation of looped water distribution networks (WDNs) has been recognised as an NP-hard combinatorial problem which cannot be easily solved using traditional mathematical optimisation techniques. This article proposes the use of a new version of heuristic particle swarm optimisation (PSO) for solving this problem. In order to increase the convergence speed of the original PSO algorithm, some accelerated parameters are introduced to the velocity update equation. Furthermore, momentum parts are added to the PSO position updating formula to get away from trapping in local optimums. The new version of the PSO algorithm is called accelerated momentum particle swarm optimisation (AMPSO). The proposed AMPSO is then applied to solve WDN design problems. Some illustrative and comparative illustrative examples are presented to show the efficiency of the introduced AMPSO compared with some other heuristic algorithms.

Numerical Study on Heat Transfer Enhancement and Friction Factor of LS-2 Parabolic Solar Collector

In this work, the distribution of solar heat flux around receiver was calculated by Mont-Carlo statistical technique that has been written using matlab. The numerical investigations of convective heat transfer process, friction factor, and efficiency of LS-2 parabolic collector have been performed. Based on finite volume methods, the influence of Rayleigh number (Ra), diameter of plugs, and thermal conductivity of the tube were studied on Nusselt number, outlet temperature, and the efficiency of collector. Because of using several central plugs with different diameters, the amounts of flow velocity have been changed, as the mass flow rate of each case study was considered constant. The diameters of plug were as: 10, 15, and 25 mm, respectively. The diameter of LS-2 collector plug was 50.8 mm (r* = 0.765). So, in order to validate the numerical simulation method, the outlet temperature of LS-2 collector (Dp = 50.8 mm) was compared with Dudley et al. (Dudley, V., Kolb, G., Sloan, M., and Kearney, D., 1994, “SEGS LS2 Solar Collector—Test Results,” Report of Sandia National Laboratories, Report No. SANDIA94-1884) experimental results. Finally, the results show that, for r* 0.6 m the mixed convection is the dominant mechanism of heat transfer. Also, with the increase of plug diameter, friction factor decreases and the minimum amount of Nusselt number is occurred at r*=0.6 m.

Numerical Investigation of Local Entropy Generation for Laminar Flow in Rotating-Disk Systems

The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor.

An Investigation into Air-Sand-Water Three-Phase Flow through the Sandblasting Nozzle

The numerical analysis of air-sand-water three-phase turbulent flow through converging-diverging nozzle is investigated for employing on sandblasting systems. For this purpose-dispersed flow of air-sand-water by various airs inlet pressures and different mass flow rates of sand particles and water droplets were considered. Two-way turbulence coupling between particles/droplets and airflow as well as interference between the incident streams of particles and rebounded from the wall were applied in the numerical model. In addition, the shock wave, which is produced in supersonic flow at diverging part of nozzle, was considered. In this study the Realizable k-e and Discrete Phase models were utilized for simulating of multi-phase turbulent flow through the converging-diverging nozzle. As review of literature indicates there is not any experimental or analytical data on three-phase flow through the nozzle, consequently for validation of model, the same turbulent and multi-phase models were utilized on air-wat...

A modified numerical method for calculations of film geometry of elasto-hydro-dynamic line contacts

In this paper, a modified full numerical model will be presented to calculate elastohydrodynamic line contacts in various conditions of geometry and material properties. This model can calculate results in shortest time and with best accuracy. All modifications will be applied in previously developed models to reach demanded results in desired time and accuracy. This model is helpful to get results in large number of points in elastohydrodynamic applications as gear lubrication along path of contact). Firstly, a scheme of the method will be presented. Then, some changes will be made in calculation process and considering the time consumption and results accuracy, the best method will be chosen. Finally, a special guess method will be developed to get the numerical results in the shortest time and best accuracy. In this method, firstly a good guess will be obtained using a coarse grid and short time and then these values will be used as a realistic guesses for starting numerical method in fine grid. Some special results will be obtained and discussed investigating the convergence process.

Analysis of the hydrodynamic torque effects on large size butterfly valves

Butterfly valves are widely used in various industries such as water distribution, sewage, oil and gas plants. The hydrodynamic torque applied on the butterfly valve disk is one of the most important factors which should be considered in their design and application. Although several methods have been used to calculate the total torque on these valves, most of them are based on the hydrostatic analysis and ignore the hydrodynamic effect which has a major role to determine the torque of the large-size valves. For finding the dynamic-valve-torque, some empirical formulas and methods have been proposed, for example in AWWA C504 standard; a relationship for calculating the dynamic torque has been given and its variation versus disk angle has been stated. However using these empirical relationships is restricted due to the conditions defined in the standards. In this paper, the dynamic-valve-torque has been calculated for a large size butterfly valve under different conditions and also at the different opening angles of the valve disk. For this purpose a Computational Fluid Dynamics (CFD) method has been used. The results have been compared with those given in the AWWA C504 standard recommendations. Moreover, the effects of the disk shape and its deformation, surface roughness, upstream/downstream pressure variation and disk-offset value have been studied.

Computation of Velocity Profiles and Pressure Coefficients for a Laminar Flow of Air Over Staggered Array of Tubes

In this study a two dimensional, steady state and incompressible laminar flow for staggered tube arrays in crossflow is investigated numerically. A finite-volume method is used to discretize and solve the governing Navier-Stokes equations for the geometries expressed by a boundary-fitted coordinate system. Solutions for Reynolds numbers of 100, 300, and 500 are obtained for a tube bundle with 10 longitudinal rows. Local velocity profiles on top of each tube and corresponding pressure coefficient are presented at nominal pitch-to-diameter ratios of 1.33, 1.60, and 2.00 for ES, ET, and RS arrangements. Differences in location of separation points are compared for three different arrangements. The predicted results on flow field for pressure coefficient showed a good agreement with available experimental measurements.Copyright