compressible 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 research explores and compares the AUSM scheme family based on compressible, steady, viscous, and inviscid axisymmetric flows in a finite-volume method-based and unstructured data storage grids code. When the effects of side-velocity are taken into account, axisymmetric flows can be considered a three-dimensional problem in the longitudinal plane; as a result, there is a considerably decreased number of computations required compared to computations in three dimensions. The most important and latest modifications of the AUSM-family were developed to identify more efficient methods in the AUSM- family in terms of accurate prediction of the axisymmetric flow field in internal and external axisymmetric flows, viscous (inviscid), and high-speed flows with shock waves characteristics. The novelty of this investigation is the assessment and comparison done on the AUSM-family in resolving the compressible axisymmetric flow field, which has received less attention in prior studies. The studies determined that the AUSM+M method performs better against a strong shock wave than other methods investigated in this research. According to the modifications made in this scheme, unlike other methods, there are no wiggles in the regions mentioned earlier. Furthermore, it is discovered that the AUSM+M method had a higher rate of convergence than the AUSM+ and SLAU approaches. In addition, the AUSM+M scheme is distinctive from other techniques in viscous flows because it produces the minimum kinetic energy dissipation rate and fewer shock anomalies in the shock wave region.

Solving many important industrial problems requires knowing the values of the heat transfer coefficient of passing of one or more fluid streams in different equipment, systems or pipes. In the present study, a numerical model has been developed to simulate compressible fluid flow at the inlet of a hot pipe with different angles to the horizon. In this zone, the hydrodynamic and thermal boundary layers of the fluid flow are developing. Due to the turbulence of the fluid flow due to the interaction of heat and fluid flow inside this tube, a three-dimensional turbulent model was used for this simulation. For this purpose, continuity and compressible Navier-Stokes equations, Reynolds stress model, and turbulent and compressible energy equation have been solved simultaneously. Then, using a set of numerical runs by the concepts of experimental design and optimization methods, a predictive formula for the Nusselt number for these flows has been obtained. Finally, the ability of this formula has been investigated using a set of laboratory data.

When a shock wave propagates through a flow field that has nonlinear thermodynamic properties, different processes occur simultaneously. Wave compression, wave refraction, and vortex generation are examples of these processes that cause the waveform and thermodynamic properties of the fluid to change. The interaction of a shock wave with a cylindrical bubble is an example of a wave-bubble collision problem in which all of the above processes are observed. Due to the high computational cost of density-based algorithms in solving compressible interfacial flow problems such as shock wave interaction with the two-phase flow, using a fully coupled pressure-based algorithm is a good solution that will solve the problem with proper accuracy while reducing computation time. In this paper, using this algorithm, the interaction of the shock wave with the bubble is investigated; while validating the results, the effect of the computational grid size and the method of discretization of the governing equations are determined. It was observed that by increasing the number of computational grids according to the first-order upwind method, the simulation results become more accurate, and the numerical diffusion amount decreases. Also, by changing the discretization method to second-order upwind, the instabilities on the interface of the two phases increase due to spurious fluctuations, and the shape of the interface obtained from the numerical solution moves away from the experimental results.

In this paper, the water hammer resulting from the fast closure of the valve in a pipeline is simulated using numerical solution of continuity and Navier-Stokes equations. Simulation has been performed for a high-viscosity oil and for water. The initial flow regime for water is turbulent and for the oil is laminar. The obtained results are compared with the experimental results and for both fluids, a good agreement between the simulation and experimental results at different times is obtained. Velocity contours at different times show two regions with different behavior in transient flow. The wall region and the pipe core region. In the wall region, the effects of fluid viscosity are dominant, the velocity gradients are sharper, and flow changes more rapidly. While the pipe core region is affected by fluid inertial forces. As the fluid viscosity decreases and the Reynolds number increases, the core region becomes larger. In addition, a parametric study has been conducted and the effect of different parameters on water hammer has been studied. The results show that by reducing the thickness or length of the pipe, reducing the mass flow rate, or using a pipe with a lower elastic modulus, the water hammer effects can be significantly reduced. For example, by reducing the length of the pipe from 60 meters to 18 meters, the maximum pressure decreases by 11%.

The comprasion of AUSM Family through the Controle volume method and an unstructured data storage strategy is conducted in this research. Evaluation of the compressible-flow scheme solutions in unsteady flows, due to their time-dependence complications can provide an insight into such solutions to recognize and explaine their strengths and weaknesses. Accordingly, in order to identify the more efficient methods in the broad category of the AUSM family in terms of accurate prediction of the characteristics of unsteady flow fields, the AUSM family was evaluated by performing 1D and 2D shock tube tests. Distinctively, the present work evaluates a majority of the legendary modifications proposed to the AUSM scheme, in the 1D and 2D unsteady tests to formulate the most efficient yet accurate solution strategy. Based on the analysis, it was found that, in the 1D test, the SLAU-based methods, rather than the modified AUSM schemes, offered better potentials for predicting the expansion and compressive waves. It was further revealed that, among the various modifications made to the AUSM, the AUSM+M and AUSMSV led to better outcomes. In the 2D shock tube test, the ASUM+, AUSM+FVS, and AUSMPW, which exhibited no or merely subtle vibrations in the 1D test, were found to be strongly affected and exhibited intensive instabilities

In this study, numerical simulation of a pulse-jet filter cleaning system is conducted and its performance is investigated under pre-defined conditions. In the first step, 3D simulation of the system from high pressure tank to filter inlet is performed and the output is used as the input of second step. In second step, simulation is performed for filters with inlet mass flow rates calculated from the previous step. To validate the results, the results are compared to experimental data showing acceptable agreement. The results show that regardless of valve type, cleaning pulse generates after 0.5s and suddenly decreases afterward. No shock or choking is observed in the system. Another interesting result is induced flow generated after the nozzles, which increases filter inlet mass flow rate. In addition, axial distribution of filter outlet flow rate is not uniform, degrading from inlet to outlet. Finally, a complete parametric study is performed to investigate the effect of the tank pressure on the pressure difference in the filter which is an important index in cleaning performance analysis.