unsteady flow

The purpose of this study is to investigate the behavior of a cylinder with three fins in the presence of free air flow. This study aims to investigate the unsteady aerodynamic flow with respect to its practical significance in aviation. Considering the degree of freedom of movement within the geometry and the complexity of the vortex masses that cause instability, it is essential to accurately predict the different dynamic behaviors. We have investigated the dynamic behavior of the model with different length ratios, free flow speeds, and angles of attack. According to the results of the study, rotational and oscillating behaviors, as well as a combination of both, are observed, and they are dependent upon the geometrical characteristics of the model, such as the ratio of the length of the plates to the radius of the cylinder, as well as the angle of attack When the aspect ratio and free flow speed are low, the motion pattern is damped around 60 degrees and the motion regime is oscillatory in nature, which changes to rotational motion as the aspect ratio and flow speed increase. The maximum oscillation or rotation is related to the initial angle of attack of zero degrees. It has been observed that rotational motion regimes occur with an increase in the longitudinal ratio and free flow speed at low initial angles of attack.

In this study, the effect of blowing jet parameters, which include location, blowing angle, momentum coefficient, and orifice area, on the average aerodynamic coefficients and aerodynamic performance parameter of the NACA0012 is investigated. The airfoil has a sinusoidal oscillating motion around a quarter of the chord. As a result of this movement, the angle of attack of the airfoil changes from -5 to 25 degrees. Five locations by 1, 4, 6, 10, and 20% of the chord length were examined and the results showed that the placement of the jet at 1% of the chord length is more appropriate than the other locations and significantly improves performance and have more impact on the flow control. Three angles of 30, 60, and 90 degrees were considered as the angles of the blowing jet and it was observed that the angle of 60 degrees is better in controlling the flow than the other two angles and this effective angle decreases when orifice length increases. The results show that there is no regular uptrend or downtrend for the angle effect. For the jet momentum coefficient, which actually aimed to investigate the effect of blowing jet velocity, the values of 0.14, 0.08, and 0.04 were considered while the orifice length is considered constants for these cases. The results showed that increasing the blowing jet velocity as well as increasing the jet orifice length improves aerodynamic performance, although increasing the orifice length at a constant momentum coefficient decreases the mean of lift coefficient.

The common carotid artery is a large vessel which supplies oxygenated blood to the large front of the brain. The artery geometry is extracted from computed tomography angiography images of a healthy 20-year-old volunteer. ANSYS-Fluent commercial software is utilized to simulate the blood transient laminar flow in common, external and internal carotid arteries. In addition to the Newtonian viscosity model, two non-newtonian generalized power law and the modified Casson models have been selected for comparison. The quantitative and qualitative results include the distribution of the low density lipoprotein concentration, the wall shear stress and its fluctuations, and the volume and shape of the recirculation zone. Computations show that the low density lipoprotein Concentration estimated by non-Newtonian models is higher than by the Newtonian model. On the other hand, the carotid bulb and the beginning part of the external carotid artery, contain a large volume of the recirculation flow. Also, the low density lipoprotein particles concentration Comparison between the two modified Casson and Newtonian models in the common carotid artery zone shows the difference of about 12.5 percent. The results of this study show that the vortex region volume and shape are changed during the cardiac period cycle. The findings also reveal that Newtonian and non-Newtonian models present different results in predicting the flow parameters and secondary flow estimation.

The first step in turbine blade design is to select TSR. Therefore, an optimization procedure should be applied to find the best ratio since this directly affects the energy generated from the turbine. In this research the optimum TSR are calculated with regard to the dynamic stall phenomenon. The dynamic stall imposes large amplitude loading on airfoil sections and since it occurs in HAWT operating envelope in unsteady flow. The purpose of this study was to investigate the effect of unsteady flow with periodic oscillation on the performance of HAWT turbines. A DS model is implanted to analyze the static data. Then the Beddoes-Leishman DS model was tailored to the HAWT environment. Then, using this model and BEMT, the optimal TSR is calculated And the impact of the presence of dynamic stall is shown. Also, Cp and CT are plotted in several different TSR with different time steps to express the effects of Unsteady phenomenon. In addition to dynamic results, static and steady results are plotted in power and thrust graphs. This phenomenon affect the efficiency by -3% as compared to the static stall. Also the Optimum TSR increases in dynamic mode. Examination of the time average diagrams of the drag coefficient shows that the delay in separation starts approximately from the midpoints of the blade and reaches the maximum value at the root.

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

This paper presents a numerical algorithm for solving unsteady viscous incompressible two–dimensional (2D) Navier–Stokes equations. In the proposed method, for discretization of time derivatives and solving the Poisson equation of the pressure, Meshless Local Petrov-Galerkin (MLPG) and forward finite difference methods are employed, respectively. In the present analysis, the moving least-square (MLS) approximation is regarded for interpolation, and the Gaussian weight function is used as the test function. To satisfy the boundary conditions, the penalty approach is applied. In the numerical examples, the accuracy and efficiency of the method are compared with those of the exact solutions. The effects of the number of nodes, the size of time interval, as well as the nodes distribution (both regular and irregular) on the relative errors are investigated. Moreover, the Gaussian integral sub-domains with the circular and square shapes are considered, and the accuracy of the results is compared with each other. Analysis of these results for 2D benchmark geometries with different boundary conditions clearly displays that the accuracy of the suggested combined method for solution of the problem related to unsteady viscous incompressible 2D flows is high such that its differences with analytical solution is negligible. Since no limitations is considered on the design process of the regarded numerical algorithm; therefore, it is respected that this approach is successful and has sufficient efficiency to solve the governing equations.

In the present study, a software has been developed using the unsteady Reynolds-averaged Navier–Stokes method to simulate time variation of turbulence coherent structure and reduce computational cost and it is used for numerical simulation of a jet in the cross nozzle flow, accurate determination of the flow structure and nozzle fluidic thrust vectoring. Since this software can capture time dependent physics, in this paper, its capability has been investigated in the simulation of pulse jet in nozzle cross flow and variation of the fluidic thrust vectoring for three frequencies, 50, 100, and 200 Hz. Firstly, software validation has been performed by comparison the results with some experimental data, next, variation of jet in cross flow and its effect on the exhaust flow field and nozzle surface pressure distribution have been studied. Governing equation on the unsteady Reynolds-averaged Navier–Stokes algorithm has been explained and time step and applied boundary conditions have been presented. The Finite volume approach has been used for numerical discretization and the advection upstream splitting method has been utilized for flux computing. Also, to improve the solution accuracy, the multi-block grid and 2nd order monotonic upwind scheme for conservation laws method have been applied and to reduce computational time, the open multi-processing parallel approach has been used.