Mojtaba Tahani

University of Tehran | UT · Faculty of New Sciences and Technologies, University of Tehran

In the field of fluid mechanics, traditional turbulence models such as those based on Reynolds-averaged Navier–Stokes (RANS) equations play a crucial role in solving numerous problems. However, their accuracy in complex scenarios is often limited due to inherent assumptions and approximations, as well as imprecise coefficients in the turbulence mod...

In recent years, energy harvesting from vortex-induced vibration (VIV) of a cylinder as a renewable source of energy has been increased. The main goal is to enhance the harnessed hydrokinetic energy of the VIV converters. In this work, the effect of adding a rotational degree of freedom by giving eccentricity to the circular cylinder is investigate...

Physics-informed neural networks (PINNs) are successful machine-learning methods for the solution and identification of partial differential equations (PDEs). We employ PINNs for solving the Reynolds-averaged Navier-Stokes (RANS) equations for incompressible turbulent flows without any specific model or assumption for turbulence, and by taking only...

Water transmission lines have considerable hydraulic potential that can be used in hydropower plants to produce energy. The pump as turbine (PAT) is an applicable tool that provides acceptable viability. Due to the large annual consumption variations in transmission lines, the optimization of parallel PATs for regulating pressure simultaneous with...

Physics-informed neural networks (PINNs) are successful machine-learning methods for the solution and identification of partial differential equations (PDEs). We employ PINNs for solving the Reynolds-averaged Navier–Stokes (RANS) equations for incompressible turbulent flows without any specific model or assumption for turbulence, and by taking only...

Purpose Nowadays flaps and winglets are one of the main mechanisms to increase airfoil efficiency. This study aims to investigate the power performance of vertical axis wind turbines (VAWT) that are equipped with diverse gurney flaps. This study could play a crucial role in the design of the VAWT in the future. Design/methodology/approach In this...

Purpose The overall performance of an aerial vehicle strongly depends on the specifics of the propulsion system and its position relative to the other components. The purpose of paper is this factor can be characterized by changing several contributing parameters, such as distance from the ground, fuselage and wing as well as the nacelle outlet vel...

Supercritical airfoils have an unknown behavior at incompressible flow regime and Reynolds numbers lower than those related to their design point at transonic condition. In this work, boundary layer transition is studied over a supercritical airfoil by means of hot-film and pressure measurements completed with numerical simulations. The experiments...

Nowadays, concerns arise because of the depletion of fossil fuel resources that forced scientists to develop new energy extraction methods. One of these renewable resources is tidal energy, where Iran has this potential significantly. There are many ways to obtain the kinetic energy of the fluid flow caused by the moon's gravitational effect on sea...

Nowadays, by increasing energy demand and considering the importance of environmental issues in recent decades, the use of renewable energies is expanding. Among renewable energies, wind power and its technology are growing and evolving more rapidly. Resource assessment in Iran has revealed the significant potential of wind energy around the countr...

Increasing Renewable energies efficiency and harnessing the available potentials are among the goals that have been addressed in sustainable development. Helping to promote the utilization of these valuable and reliable sources can provide a basis for their worldwide expansion. Pump as turbine (PAT) is a suitable device to generate clean energy fro...

Nowadays, to extend the application of clean energy sources, the utility of small power plants has been expanded and one of them is the potential utilization of water distribution networks (WDNs). By replacing pressure reducing valve (PRV) with a soft pressure regulating system (SPRS) the available hydraulic energy could be employed for generating...

Water injection in stationary gas turbines is effective strategy for power augmentation and gas turbine efficiency improvement, in particular, at high ambient temperatures. In this study, a developed method for simulation of wet compression processes is introduced. This method is followed by the droplet evaporation analysis, aero-thermodynamic stag...

Purpose-One of the best methods to improve wind turbine aerodynamic performance is modification of the blade's airfoil. The purpose of this paper is to investigate the effects of gurney flap geometry and its oscillation parameters on the pitching NACA0012 airfoil. Design/methodology/approach-This numerical solution has been carried out for differen...

Purpose One of the best methods to improve wind turbine aerodynamic performance is modification of the blade’s airfoil. The purpose of this paper is to investigate the effects of gurney flap geometry and its oscillation parameters on the pitching NACA0012 airfoil. Design/methodology/approach This numerical solution has been carried out for differe...

Wind turbines have been used to harvest clean energy for many years. However, wind turbine simulation is extremely expensive as it requires a high computational cost. Consequently, many studies have proposed different methods to reduce the computational time of wind turbine simulation. Reduced Order Methods (ROMs) show their capability to predict t...

In this study, Computational Fluid Dynamics simulations are carried out to assess the effect of duct geometry on power output and flow characteristics for a custom-designed wind turbine. The results show that the elevation of power output for a wind turbine is strongly reliant upon the shape of the duct. While before reaching a certain tip speed ra...

Three turbulence models, namely K-ω SST, SAS and DDES, are compared with each other and reported experimental and numerical data. Rigid and sliding movements of the grid are applied to simulate the pitch oscillation and accuracy of the numerical setup is validated based on wind-tunnel data. In a certain Mach number, shock-buffet instability occurs...

In these days, energy, water, fossil fuel restrictions and greenhouse gas emission have become the mutual problem of all countries. The application of hydro turbines, especially pumps as turbines in water distribution network, can be a great solution to these problems. In this research study, it is aimed to introduce a procedure for obtaining the o...

In this research study, a physics-based optimization algorithm, namely Flow Regime Algorithm (FRA) is proposed. The main sources of inspiration are classical fluid mechanics and flow regimes. The flow regime usually is being divided into two categories which are laminar and turbulent flows. Reynolds number is the parameter which defines that the fl...

Given the widespread usage of centrifugal pumps for handling viscous fluids in various industries, improving the performance of these oil pumps has been attractive for both academic researchers and companies. In this study, we demonstrated a high drop in the performance of centrifugal pumps for handling viscous oil using a numerical simulation mode...

Purpose In this paper, experimental and numerical results of a lambda wing have been compared. The purpose of this paper is to study the behaviour of lambda wings using a CFD tool and to consider different numerical models to obtain the most accurate results. As far as the consideration of numerical methods is concerned, the main focus is on the ev...

Purpose In this paper, the applicability of shear stress transport k - ω model along with the intermittency concept has been investigated over pitching airfoils to capture the laminar separation bubble (LSB) position and the boundary layer transition movement. The effect of reduced frequency of oscillations on boundary layer response is also examin...

In this research study a novel human inspired optimization algorithm namely Team Arrangement Heuristic Algorithm (TAHA) is proposed, based on the pyramidal structure of a company and also the activities of each member in the company. It is assumed that in a company three groups of members do activities, which are the CEO, directors and employees. T...

ABSTRACT This paper describes the experimental study of surface pressure over a supercritical airfoil which was oscillated in pure pitching, pure plunging and combined pitch-plunge motions at the Reynolds number of 8.76*105. While the surface pressure distribution is of significant importance in stability and performance of an airfoil, not sufficie...

In this study, blade element momentum (BEM) theory has been used to calculate power output and performance of 100 kW and 1 MW horizontal axis wind turbine. Riso‐A1‐21 airfoils are considered as utilized section along the blade span. Generally, Riso family of airfoils is appropriate for wind turbine application. In order to improve the accuracy of t...

Stochastic behavior of renewable energy sources forces designers to optimize the energy converters for the purpose of capturing the maximum amount of available energy. The performance of horizontal axis wind and tidal turbines mainly depends on the geometrical properties such as chord and twist distributions and also the types of sections which are...

Nowadays, the optimal use of energy is one of the most important things in energy engineering. Disadvantages of fossil fuels make renewable and cleaner energy sources more widely used. Wind energy is a type of clean energies that will help humanity transition to a sustainable future. The power of wind turbine depends on many parameters such as wind...

In this research study, the optimization study of an airfoil type Savonius turbine is presented, focusing on maximizing the power coefficient. For this purpose, a Discrete Vortex Method (DVM) code for calculating power coefficient, a Class Shape Transfer (CST) function code for generating coordinates of airfoils and a Salp Swarm Algorithm (SSA) cod...

Today, one of the useful methods of flow control, especially external aerodynamics, is plasma DBD actuators. In this study, the effect of plasma DBD actuators on cylinders in tandem arrangement is investigated. The actuators are considered on upstream cylinder. The cylinders are placed in distance (L/D) relative to each other. Investigation is done...

The ongoing development driven by the progression of technology and science is leading to enhanced energy consumption. Most of the in-use energies are from restricted fossil fuel and most of the fossil fuel consumers are spark-ignition engines. On the other hand, the main duty of the development engineer is to decrease cost and increase power outpu...

In this paper, the effect of ignition timing on exergy has been investigated. At the first step, 3D-scheme numerical simulation of a complete engine cycle including combustion process has been taken to account for S81 engine geometry. 3D computational modeling process requires complete simulation of flow field in a fine mesh geometry which includes...

In this chapter, aerodynamics analysis of Vestas V47 wind turbine is implemented by the use of modified blade element momentum (BEM) theory to determine aerodynamics performances such as output power, axial, and tangential forces which can be coupled with structural analysis to predict aeroelastic behavior of wind turbine blade. Unlike most BEM ana...

This research paper mainly deals with a thermodynamic modeling and exergy analysis of a hybrid energy system consisting of a solar PV/T panel, PEM electrolysis, a polymer fuel cell (PEMFC), and single-effect Li-Br absorption chiller. Hydrogen is produced in this cycle using the electricity generated by PV/T panel, and it is stored in storage for la...

Purpose Given the importance of airports and the need to develop this issue in runway, in this paper, pavement response values under loading of different aircrafts have been obtained using tire and pavement modeling by FEM. To predict the actual behavior of pavements under aircraft loading, dynamic analysis of runway flexible pavement was performe...

Purpose In this paper, numerical solution of transonic flow around NACA0012 airfoil is investigated under sinusoidal pitch oscillation. Accordingly, effects of the amplitude and frequency of oscillations on aerodynamic coefficients are evaluated and the efficiency of the turbulent models, K-ω SST, SAS and DDES, in simulation of the nonlinear pheno...

Purpose This paper aims to analyze the influence of the changings in geometrical parameters on the aerodynamic performance of the control canard projectiles. Design/methodology/approach Because of the mentioned point, the range of projectiles increment has a considerable importance, and the design algorithm of a control canard projectile was fir...

Recently, Savonius vertical axis wind turbines due to their capabilities and positive properties have gained a significant attention. The objective of this study is to design and model a Savonius-style vertical axis wind turbine with direct discharge flow capability in order to ventilate buildings. For this purpose, a modeling procedure is defined...

In this study, the surface vorticity method based on the Biot-Savart law is implemented for analyzing the ducted horizontal axis wind turbine to calculate the aerodynamic performance. The present method requires considerably less computational time than CFD methods. Our goal is to present a method for considering the effects of the duct on the wind...

Due to the growing rate of the cost of energy carriers and the shortage of different kinds of fuels, day by day it becomes more essential to use renewable energies such as wind, solar, hydrogen, geothermal, etc. The application of renewable energies for household use is an ideal solution to reduce enviromental pollution. It is possible to use diffe...

Purpose This paper aims to investigate the aerodynamic characteristics as well as static stability of wing-in-ground effect aircraft. The effect of geometrical characteristics, namely, twist angle, dihedral angle, sweep angle and taper ratio are examined. Design/methodology/approach A three-dimensional computational fluid dynamic code is develop...

In the present research, by using the modification in some of geometrical parameters, the performance of viscous fluid centrifugal pumps has been improved. In other words, the effects of the inlet and outlet blade angles and passage width have been investigated. Numerical simulation of three-dimensional flow is carried out by an extended computatio...

In this research study it is aimed to propose a novel heuristic method for optimizing the VAWT design. The method is the combination of continuous/discrete optimization algorithms with double multiple stream tube (DMST) theory. For this purpose a DMST code has been developed and is validated using available experimental data in literature. A novel...

Purpose This study aims to investigate effects of sonic jet injection into supersonic cross-flow (JISC) numerically in different dynamic pressure ratio values and free stream Mach numbers. Design/methodology/approach Large Eddy simulation (LES) with dynamic Smagorinsky model is used as the turbulence approach. The numerical results are compared...

The country's industrial development has led to increment in consumption of energy. Thus, energy saving is substantial in developed countries. Due to implement of cement in industry construction, authentic manufacturing method is essential. Cement is considered as high consumed source for industry which requires high productivity. On the other hand...

One of the affordable ways to produce energy is using the wind power by the wind turbines. Therefore, studying and improving the performance of these turbines is important. Most of the wind turbines have to operate in the high turbulence intensity which is typically due to the turbulence of the lower layers of the atmosphere or vortices caused by t...

In this study aerodynamics analysis of full scaled Vestas V47 wind turbine is carried out by the use of modified blade element momentum (BEM) theory and computational fluid dynamics (CFD). In order to determine accurate results BEM theory is programmed by considering drag coefficient, Glauert correction and Prandtle tip loss factor. CFD simulation...

In this paper a certaine type of wind turbine has been simulated and its foundations' directions has been controled by fuzzy logic. This turbine model collection has seven degree of freedom and turbine directional movement controls by placing three jacks on three bases and using powers on bases. Movement control has been done by considering two mov...

Pumping of oil instead of water using centrifugal pumps causes rapid increase in the hydraulic losses which results significant reduction in head and efficiency. Therefore, deriving analytical methods to calculate variation of pump performance parameters versus working fluid viscosity is very important. In the present study, a novel method is propo...

In this paper, the numerical solution of transonic flow around the NACA0012 airfoil is investigated under the sinusoidal pitch oscillation. Accordingly, effects of the amplitude and frequency of the oscillations on aerodynamic coefficients are evaluated and the efficiency of the turbulent models, K-ω SST, SAS 2 and DDES, in simulating the nonlinear...

Improving the working fluid transport properties is a way to enhance the thermal performance of heat transfer equipments. In this research work, a two-dimensional numerical simulation is used to investigate the thermal performance of a nanofluid filled cylindrical heat pipe. The considered nanofluid is pure water as the base fluid with dispersed Al...

In this study aerodynamics analysis of full scaled Vestas V47 wind turbine is carried out by the use of modified blade element momentum (BEM) theory and computational fluid dynamics (CFD). In order to determine accurate results BEM theory is programmed by considering drag coefficient, Glauert correction and Prandtle tip loss factor. CFD simulation...

In recent years, energy predicament and environmental problems in the world caused by fossil fuels combustion make us to pay serious attention to optimizing energy consumption and using renewable energies. One of the potential renewable energies which can be helpful in electricity generation is harness wind and water energy or using these two kinds...

In this chapter, the results of three-dimensional computational fluid dynamics (CFD) finite volume simulations of airflow around a commercial Vestas V80 Horizontal Axis Wind Turbine (HAWT), with a rated output power of 2 MW, are presented. The grid used in the simulations consists of two main parts, i.e., unstructured mesh rotating with blades and...

This research paper mainly deals with thermodynamic modeling, exergy analysis and optimization of a hybrid energy system consisting of a solar PV/T panel, PEM electrolysis, and a polymer electrolyte membrane (PEM) fuel cell and single effect Li-Br absorption chiller. Hydrogen is produced in this cycle using the electricity generated by PV/T panel a...

In the present work, four turbulence models and their precision on results for twenty-two cases of different wind speeds, ranging from cut-in to cutoff values, and associated mean pitch angles of blades are investigated numerically. The results of 3D finite volume simulations of airflow around a commercial Vestas V80 horizontal axis wind turbine (H...

In this research paper, a comprehensive thermodynamic modeling of a combined cycle power plant is first conducted and the effects of gas turbine inlet fogging system on the first and second law efficiencies and net power outputs of combined cycle power plants are investigated. The combined cycle power plant (CCPP) considered for this study consist...

Wind power has been widely considered and utilized in recent years as one of the most promising renewable energy sources. In the current research study, aerodynamic analysis of the upwind three-bladed horizontal axis turbine is carried out using blade element momentum theory (BEM), and a genetic algorithm (GA) is applied as an optimization method....

In this study, an input stream of symmetrical supersonic inlet with boundary layer suction has been investigated by using of two-dimensional full Navier - Stokes equations. The analysis has been performed for three various Mach numbers. The main purpose of this study is reduction of adverse pressure gradient for performance improvement of supersoni...

Centrifugal pumps performance is highly affected by working fluid viscosity. So, optimization of such pumps for pumping of viscose fluids is very important. In the present paper, multi-objective optimization of the centrifugal pumps is performed to obtain optimum impellers for pumping fluids with various viscosities at different volumetric flow rat...

In this study the performance and emissions characteristics of a heavy-duty, direct injection, Compression ignition (CI) engine which is specialized in agriculture, have been investigated experimentally. For this aim, the influence of injection timing, load, engine speed on power, brake specific fuel consumption (BSFC), peak pressure (PP), nitrogen...

Al-Mg and CuZn34 alloys were lap joined using friction stir welding while the aluminum alloy sheet was placed on the CuZn34. In addition, the mechanical properties of each sample were characterized using shear tests. Scanning electron microscopy (SEM) and X-ray diffraction analysis were used to probe chemical compositions. An artificial neural netw...

In this investigation, the effects of spike as retractable drag and aerodynamic heating reduction into the reentry Earth’s atmosphere for hemispherical body flying at hypersonic flow have been numerically studied. This numerical solution has been carried out for different length, shapes and nose configuration of spike. Additional modifications to t...

a b s t r a c t In this research Al–Mg and CuZn34 alloys were lap joined using friction stir welding during which the aluminum alloy sheet was placed on the CuZn34 and the process parameters were optimized using Tagu-chi L9 orthogonal design of experiments. The rotational speed, tool tilt angle and traverse speed were the parameters taken into cons...

In this study the effects of induced jet at trailing edge of a two dimensional airfoil on its boundary layer shape, separation over surface and turbulent parameters behind trailing edge are numerically investigated and compared against a previous experimental data. After proving independency of results from mesh size and obtaining the required mesh...

The performance of centrifugal pumps drops sharply during the pumping of viscous fluids. Changing some geometric characteristics of the impeller in these types of pumps improve their performance. In this investigation, the 3-D flow in centrifugal pump along with the volute has been numerically simulated. This numerical solution has been carried out...

There are a substantial amount of waste heat through exhaust gas and coolant of an internal combustion engine. Organic Rankine cycle is one of the opportunities in internal combustion engines waste heat recovery. In this study, two different configurations of organic Rankine cycle with the capability of simultaneous waste heat recovery from exhaust...

Essentially, performance of centrifugal pumps is affected when pumping viscous fluids. In this paper a new idea is proposed to overcome the undesirable effects of viscosity on the pump performance parameters. This idea based on this matter that one specific impeller can be designed, made and installed on the pump for pumping of one fluid with speci...

Thermal modeling and optimal design of compact heat exchanger is presented in this paper. Fin pitch, fin height, cold stream flow length, no-flow length and hot stream flow length were considered as five design parameters. A CFD analysis coupled with artificial neural network was used to develop a relation between Colburn factor and Fanning frictio...

Airfoil in ground effect characteristics is important in aircraft take off and landing and in WIG vehicle design. WIG crafts operate close ground. Flow over the NACA 0015 is investigated numerically with two different models of k-ε model, Realizable and RNG, the result compared with experimental study. Studies were performing in 2.5 and 7.5 degree...

Inlet fogging has been widely noticed in recent years as a method of gas turbine air inlet cooling for increasing the power output in gas turbines and combined cycle power plants. The effects of evaporative cooling on gas turbine performance were studied in this paper. Evaporative cooling process occurs in both compressor inlet duct (inlet fogging)...