turbulent flow

In this article, the focus is on compressible fluid, which has not been simulated in geometry with very large dimensions and high speed. Also, the method of large eddies has higher accuracy in turbulent flow modeling than other numerical simulation methods.The desired geometry is a cube with dimensions of 30 meters, and we have performed the simulation in two spatial and temporal modes separately for 100 seconds. The inputs are different in different modes so for the spatial mode, we have considered two inputs in the same direction with different speeds, and for the time mode, we have considered two inputs in opposite directions and with the same speeds. The general results obtained from this simulation showed that when the inlets are next to each other and the vortices' opposition is greater, we see more turbulence, kinetic energy and strength of the vortices and their larger size. But in the temporal mode, because the inputs are far from each other, the confrontation was not done well, so we observed less strength of eddies and smaller eddies and little spread compared to the spatial mode.

This study was conducted to investigate the effect of magnetic field on Hartmann numbers ranging from 50 to 200 in a parabolic solar collector with zero to 2.25 percent volume fraction of magnetic hybrid nanofluid containing three nanoparticles of iron oxide, multi-walled carbon nanotubes, and copper in the Reynolds number range of 18000 to 42000. In the numerical study, a parabolic solar collector was simulated using the finite volume method, and the thermophysical properties of the magnetic hybrid nanofluid were used as the working fluid in it. The solar collector absorber tube under study is equipped with three different geometric shapes of turbulators. A hybrid nanofluid of water/carbon nanotube multi-wall-iron oxide-copper has been considered for two-phase simulation. According to numerical results, the maximum exergy efficiency is related to the absorber tube equipped with a combination of turbulator and circular wire. Additionally, the maximum exergy efficiency is related to a Reynolds number of 18000 at a Hartmann number of 200.

Impingement jet is a fluid flow that hits a surface perpendicularly or at a specific angle for the purpose of cooling or heating. The rate of transfer processes in turbulent impingement flows is affected by the formation of coherent structures, the interaction between them and transfer of It's energy.By oscillating the incoming flow in the impinging jets, the formation of coherent structures can be affected, and as a result, the amount of heat removal is affected. In this study, the effect of pulsed impinging jet using step and sinusoidal functions The flow and temperature field of a dimpled surface has been investigated by numerical method. The key parameters in this study include the shape of the input function, the frequency and the amplitude of the oscillating jet. The results of this study have been validated using previous researches and then The effect of key parameters on the  formation of coherent structures and the amount of heat extraction have been discussed and analyzed. The results show that bypulsating the inlet flow, it is possible to change the recirculation zones and the vorticity field in the flow and overally The heat increases on the dimpled surface. Such results show that the flow patterns and Nusselt number are highly dependent on the parameters of the input function such as frequency and amplitude.

Cooling is one of the most important challenges in saving energy and increasing the productivity of many industries. The first serious obstacle in compressing and making heat transfer devices more efficient is the weak properties of heat transfer fluids. The energy efficiency of heat transfer equipment depends on the heat flux changes created in them. The use of common fluids such as water and ethylene glycol as cooling fluids in the cooling system of various heat transfer devices is not the answer to the removal of very high heat flux (tens of megawatts per square meter). Today, nanofluids are made as new heat transfer fluids by adding nanoparticles to fluids that have low heat transfer and by creating changes in the density, specific heat and viscosity of these fluids in order to increase thermal conductivity and improve heat transfer performance. In this research, the results of laboratory research on heat transfer in nanofluids under laminar, turbulent flows and pool boiling are discussed and investigated.

Due to the complexity of turbulent flows, it is not possible to solve the governing equations in full detail. Therefore, different numerical approaches have been proposed to solve the governing equations and analyze the flow characteristics. The most important methods include Direct Numerical Simulation (DNS), Large Eddy Simulation (LES) and Reynolds Averaged Navier-Stokes Equations (RANS). In terms of accuracy and computational cost, large eddy simulation is in between two other methods. In this method, large and small scales are separated by applying a low-pass filter. Large scales are solved and small scales are modeled. So far, various models have been presented for small or subgrid scales. Eddy viscosity models are the most common models used for this purpose. The first and simplest eddy viscosity model is the standard Smagorinsky model. The accuracy of this model is low, especially for complex geometries. Therefore, various studies have been conducted to increase the accuracy of this model. The dynamic Smagorinsky model, dynamic localization model, and scale-dependent dynamic model are among the most widely used models. In this paper, the progress of eddy viscosity models used in large eddy simulation is presented.

Electromagnetic flowmeters are high-precision devices that can be used to measure fluid flow in engineering systems, including municipal water supply networks. In this research, electromagnetic flowmeter modeling has been used which is a hybrid model based on numerical simulation results of turbulent flow and data estimation method for a pipe with a diameter of 100mm and a length of 800mm. The numerical model is built using three-dimensional simulation framework by creating a magnetic field in the center of the geometry and measuring the volume flow rate using Faraday law and Maxwell equations. In fact, the physics of the problem is such that to measure the flow rate of a fluid, a magnetic field was created in the center of the geometry where the electromagnetic inductors are located. By moving the fluid that has electrical conductivity, the intensity of electromagnetic induction was obtained at that point and the amount of velocity and flow rate was calculated using these data. For this purpose, current simulation under the effect of electromagnetic intensity was performed for the values of 0.01, 0.03 and 0.05 (Tesla) to obtain the most appropriate intensity. The results show that up to an intensity of 0.03, the magnetic field has little effect on the structure of the flow field. In order to develop an alternative model of electromagnetic flowmeter, the method of estimating the inlet average velocity based on information from numerical simulation data has been used. First, for a certain number of pressures (pressure differences), the magnetic field intensity in the position of the sensors was obtained then using these values, the inlet average velocity using direct numerical simulation was calculated. A new magnetic intensity different from the values ​​used was obtained by data mining method. In order to ensure the accuracy of the results, the obtained data were compared with the calculated values ​​of the software.

In the presented research, the analysis and finding optimal values of a heat exchanger used in the exhaust system of a diesel engine has been discussed. The main purpose of using this heat exchanger is to reduce the temperature of combustion products exhausting from the engine. This can be done by mounting a heat exchanger at the exhaust gas path. In order to analyze the issue, different designs of heat exchangers have been regarded. Three- and five-tube heat exchangers reduce the temperature of the smoke to an acceptable level by increasing the contact surface between the smoke and the cooling water. However, the pressure drop created on the side of the smoke is high in these designs. The use of annular fins and longitudinal fins on the smoke side also increase the heat transfer by increasing the contact surface between the smoke and water flow and the turbulence in the smoke path. However, in this design the heat exchanger outlet temperature is higher than allowed value (350 ). Furthermore, in this design, the pressure drop also increases. After the investigations carried out to reduce the temperature of the smoke, shell and tube heat exchangers have been chosen as the final designs. The shell and tube heat exchangers is capable to reduce the exhaust temperature to 309.42 .

The most recent proposed technique for drag reduction in hypersonic flow speeds is using the exothermic coating on the blunt nose. This leads the heat addition into the flow field behind the shock wave, and increases the shock-stand-off distance. The variation of the drag force on the flying body using this technique is numerically investigated in the present study. The compressible turbulent flow is simulated around the body to compute the drag force, and to estimate the drag reduction capabilities of this technique. This quantitative analysis makes better insight to evaluate it in operational applications

Numerical study of turbulent and laminar flow is investigated for an incompressible nanofluid flow in a 2D wavy channel by using the finite volume method (FVM). The results of the Nusselt number, pressure drop, and thermal performance has obtained for diameter ratios (a/b=0, 0.25, 0.5, 0.75, 1), volume concentration(FI = 0%, 2%, 4%) and nanoparticle diameters in four Reynolds number(Re=10000, 20000, 30000, 40000). The validation was compared with analytical and numerical studies. The results shown a good convergence between them . The results showed that using wavy parts caused to increasing in heat transfer rate and pressure drop by 1.78 and 8.1 times respectively. Additionally, augmentation of the volume concentration increased the heat transfer rate and pressure drop by 2.1 and 3 times respectively. The use of laminar flow also had a higher heat transfer rate, pressure drop and, thermal performance compared to turbulent flow within the Reynolds 1000 range.