mohammad taeibi rahni

Inspiring from bird’s wings and flights has long been a fascinating subject. In recent years, due to advent of materials and implementation of bird’s flights, use of morphing wings have created considerable changes in scientific issues related to air vehicles. In this article, for the first time, aerodynamic and aeroacoustic studies of a type of (twist) morphing wing are performed. The main pupose of this article is to numerically investigate aerodynamics and aeroacoustics of a twisted morphing wing for a geometry similar to Shahed- 129 UAV. In the manufaturing part of this article, a new method is introduced, which uses actuators to change the wing’s shape. In this article, k- ω- SST modeling for turbulent flow and Fluent software were used. Our results show that with increase of twist angle and attack angle of up to 15 degrees, both lift and drag increase. In addition, at the same angle of attack, for high twist angles, increasing twist angle increases the growth of vortices, causesing a small increase in lift coefficient.

In present research, the interaction between single liquid droplet with particles inside a porous media is investigated numerically in two dimensions. The He’s model is used to simulate two phase flow and multiple relaxation time collision operator is implemented to increase numerical stability. Simulations have performed in three non-dimensional body forces of 0.000108, 0.000144, 0.000180, porosity values of 0.75, 0.8, 0.85 and Ohnesorge range of 0.19-0.76. In the range of investigated non-dimensional parameters, two distinct physics of droplet trapping and break up have observed. The related results revels that for every values of investigated non-dimensional body forces and porosity, there is a critical Ohnesorge number that droplet breaks up occurs for larger values. This critical value decreases as non-dimensional body force and porosity increases. Based on these results, a droplet trapping or break up behavioral diagram is drown with respect to the investigated density ratio, Ohnsorge, Reynolds and Capilary numbers.

In this article, the simulation methods of multiphase flow in the presence of surfactants are classified into 3 categories based on Navier-Stokes, distribution function, and based on intermolecular forces, and each one is described separately. Navier-Stokes-based methods fall into two categories: interface tracking methods and interface capture methods. Methods based on intermolecular forces act as particle-based methods with a Lagrangian perspective in dealing with the flow field. The widely used models in the methods based on the distribution function are also introduced at the end. A wide range of numerical methods has put many choices in front of researchers. Knowing and understanding the capabilities and details of these methods will help to select the most appropriate numerical method and obtain reliable and cost-effective results according to the hardware facilities.

In this article, Surface Active Agents (Surfactants) and its effect on the Multiphase Flow have been studied. First, the functioning of surfactants has been explained. For this purpose, the definitions of surface tension and how it changes in the presence of surfactants have been investigated. Also, the physics of surfactant distribution in multiphase flow and its absorption and repulsion at the interface have been reported. The physical changes of the two-phase interface due to the presence of surfactants have been investigated through the balance of forces and the change in surface tension and the definition of the Marangoni effect. Types of surfactants and their properties are stated. Finally, the important applications of surfactants in industry and daily life are mentioned in detail. This review shows that surfactants as one of the effective factors on multiphase flow need to be studied more and more. A better understanding of these materials can be very useful in manipulating and optimizing multiphase flow applications. 

ACHEON nozzle is a thrust vectoring control device in which interaction of two jet flows under the influence of Coanda effects is implemented. The effects of inlet mass flow rate and the position of septum (relative to nozzle outlet) on flow structure, thrust vectoring, and shock formation have not been paid enough attention in previous studies. However, in this study, different mass flow rates and various positions of the septum were investigated. Flow was considered turbulent, two-dimensional, stationary, and compressible and RANS approach with standard k-ε model was implemented. The equations were solved using a pressure-based finite volume method on a structured computational grid. Using different Mach and Reynolds numbers and also various positions of the septum, thrust vectoring angle, flow structure, and nozzle shock position were studied. Our results show that with increasing inlet mass flow rate, thrust vectoring angle increases. It is noted that at a certain mass flow rate, a normal shock wave is formed in the nozzle. Also, except at this special mass flow rate (with shock wave), increasing inlet mass flow rate leads to increasing thrust vectoring angle. In addition, reducing the distance between the septum tip and the nozzle outlet increases thrust vectoring angle.

The sudden spread of Covid-19 in the world has attracted everyone's attention. In addition, due to the unknown and lack of definitive treatment methods, the World Health Organization and other medical institutions recommend non-pharmacological solutions to control the virus. In this regard, one of the proposed methods is to use masks during this global epidemic as a tool to control the spread of respiratory droplets. Therefore, in this paper, we first examine respiratory events such as breathing, talking, sneezing, and coughing from an engineering perspective and their role in the spread of the virus. In addition, with the help of numerical fluid mechanics, the formation of respiratory droplets and their function in the transmission of infectious respiratory diseases have been studied. Then, the necessity of using a mask and its role in reducing the transmission of the virus is discussed.

In current research, surface reaction phenomena in several packed bed reactors have been considered. Flow field through several fractal Sierpinski carpet porous media have been simulated by LBM. The endothermic Isopropanol dehydrogenization reaction has been considered as basic reaction mechanism and two major parameters of non-homogeneity and specific area in catalytic surface reaction have been investigated. To validate our numerical method, the obtained results have been compared to a recent benchmark study and adopted very well. Also, in both cases the porosity factor retained constant (ε=0.79). The results shown that, by three times increase in specific area, the reactant conversion rate is increased significantly (approximately one order of magnitude), and the pressure drop increased (nearly 5 times), too. Also, to consider non-homogeneity arrangement, the particle arrangements from small to large and large to small have been considered. In both, the pressure drop is approximately the same. At low Re, reactant conversion of both arrangement are the same but by increasing of Re, the packed bed reactor with large to small arrangement has a little more reactant conversion.

In this paper, natural convective heat transfer of nanofluids in a uniform magnetic field between the square cavity and inner cylinder, was simulated via Lattice Boltzmann Method. The inner cylinder in square shape, diamond, and circular has been examined. Square cavity walls and inner cylinder surfaces are at a constant cold and warm temperature, respectively. The flow, temperature, and magnetic field is calculated with solving flow, temperature, and magnetic distribution functions simultaneously. D2Q9 lattice arrangement for each distribution function is used. The results clearly show the behavior of fluid flow and heat transfer between the cavity and the cylinder. The results have been validated with available valid results showing relatively good agreement. The effects of Rayleigh number, Hartmann number, void fraction and type of nanoparticles on natural convective heat transfer are investigated. This study shows that for all three geometries used with the same void fraction, type of nanofluid, and Rayleigh number, natural convective heat transfer decreases with Hartmann number. Also, when Hartmann number was had fixed, natural convective heat transferwas increased with Rayleigh number. Thus, to select the right geometry for optimum natural convective heat transfer, our needs to pay special attention to Hartmann and Rayleigh numbers. In addition, viod fraction and type of nanofulid can affect heat transfer directly.

Jet injection into a cross flow is a highly applicable problem which has been analyzed and studied in different scientific and engineering research fields. A significant problem which has attracted less attention is sound generation of jet injection flow. So flow and acoustic fields of this problem is studied by a two-dimensional large eddy simulation approach and the Smagorinsky model. This study was conducted for three different velocity ratios at constant jet Reynolds number. Spatial temporal discretizations were performed using the sixth order compact and the fourth order Runge-Kutta methods, respectively. Code verification was performed using several different problems and the obtained results were compared with the available numerical and experimental results. Main dominant frequencies of the acoustic field were obtained and investigated by applying the pressure history Fourier transform at different locations upstream and downstream of the jet. A multi-mode rather than a single-mode acoustic field was observed. In addition, various modes are activated and inactivated at different time intervals. Also, by varying the ratio of jet velocity to cross flow velocity, the sound generation mechanism and the non-dimensional frequencies that dominate the acoustic field change as well.

In this research، effects of density differences between a hot cross flow and injected coolant fluid on the flow hydrodynamics and film cooling effectiveness at different velocity ratios were computationally investigated. A computer code was developed using finite volume method and the SIMPLE algorithm on a multi-block، non-uniform staggered grid. Three different turbulence models (standard and SST versions of and) were applied. The simulations were performed at three density ratios of 0. 5، 1، and 2، and three different velocity ratios of 0. 5،1، and 2. The jet into cross flow temperature ratio and the jet Reynolds number were 0. 5 and 4700، respectively. Comparing the obtained results showed that the density ratio effects on the turbulent kinetic energy، especially in the near wall region، is noticeable. Therefore، the convection heat transfer coefficient can be greatly affected by the density ratio. In addition، the density ratio has significant effects on the jet into cross flow penetration in all three directions (streamwise، normal، and spanwise). Moreover، at low velocity ratio (0. 5)، increasing the density ratio reduces the spanwise averaged film cooling effectiveness. At higher velocity ratio (2. 0)، as the density ratio increases، the spanwise averaged cooling effectiveness increases.

In this research، effects of blowing ratio (velocity ratio) difference between the controlling small jets and the main jet in the compound triple jets arrangement on the film cooling effectiveness and the flow hydrodynamics are investigated. This blowing ratio difference was selected such that the total mass flow rate of the cold flow becomes equal to that of the simple compound triple jets. The triple jets are inclined normally into the cross flow and the cooling jets to the hot cross flow temperature ratio and the jets Reynolds number are 0. 5 and 4700، respectively. The numerical approach is based on the finite volume and the SIMPLE algorithm over a multi-block، staggered، structured and non-uniform grid arrangement was applied. The numerical simulations are performed for three controlling jets to main jet velocity ratios. The obtained results show that when the velocity ratio is higher than unity، the film cooling effectiveness increases، while it decreases when the velocity ratio is less than unity. Due to high complication of the flow (results from interaction of three jets with the cross flow) and time dependency of the introduced vortex structures، the large eddy simulation approach was used to investigated the flow more accurately.

In this study we introduce and validate an algorithm for simulating of flow field over moving boundaries where there are transverse cylinder and flapping airfoil. The governing equations are presented in arbitrary Lagrangian-Eulerian approach. We use finite element shape functions to approximate pressure and diffusion fluxes and finite volume to satisfy geometric and flow conservation laws. Our results show a good accuracy with large time steps and coarse meshes. The changing in oscillation parameters causes considerable effects on aerodynamic coefficients.