Jahanfar Khaleghinia

Bio: Jahanfar Khaleghinia is an academic researcher from Islamic Azad University. The author has contributed to research in topics: Airfoil & NACA airfoil. The author has an hindex of 4, co-authored 10 publications receiving 34 citations.

Effect of Gurney flap on flow separation and aerodynamic performance of an airfoil under rain and icing conditions

Abstract: In the present study, special attention is paid to numerically investigate the aerodynamic performance of the NACA 0012 airfoil under rain and icing conditions with the aim to better understand the severe aerodynamic performance penalties of aircraft in flight. Furthermore, in order to control the flow separation and improve the aerodynamic performance of the airfoil under critical atmospheric conditions, the Gurney flap with different heights is attached to the trailing edge of the airfoil. The simulation is done at a Reynolds number of 3.1 × 105 under different atmospheric conditions including dry, rain, icing and coupling of rain and icing conditions. A two-way momentum coupled Eulerian–Lagrangian multiphase method is used to simulate the process of water film layer formed on the airfoil surface due to rainfall. According to the results, accumulation of water due to rainfall and ice accretion on the airfoil surface inevitably provides notable negative effects on the aerodynamic performance of the airfoil. It is concluded that icing induces a higher aerodynamic degradation than rain due to very intensive ice accretion. The Gurney flap as a passive flow control method with a favorable height for each condition is very beneficial. The maximum increment of the lift-to-drag ratio is achieved by Gurney flap with a height of 0.01 of airfoil chord length for dry and rain conditions and 0.02 of airfoil chord length for icing and coupling of rain and icing conditions, respectively.

Effects of the hinge position and suction on flow separation and aerodynamic performance of the NACA 0012 airfoil

Abstract: In the present study, the effect of hinge position (H) has been numerically investigated to find the appropriate position for improving the aerodynamic performance of the NACA 0012 flapped airfoil. In addition, perpendicular and tangential suctions have been applied to control the flow separation and enhance the aerodynamic performance over the NACA 0012 flapped airfoil at each different hinge positions. The simulations were carried out at a Reynolds number of 5 × 105 (Ma = 0.021) based on two-dimensional incompressible unsteady Reynolds-averaged Navier–Stokes calculations to determine the adequate hinge position. The turbulence was modeled using the shear stress transport k–ω turbulence model. The effect of perpendicular suction (θjet = − 90°) and tangential suction (θjet = − 30°) was computationally studied over NACA 0012 flapped airfoil for five different hinge positions (H = 0.7c, 0.75c, 0.8c, 0.85c and 0.9c) and a flap deflection (δf) of 15°. Based on the results, the hinge position significantly affects the aerodynamic performance of the airfoil. The lift coefficient increased clearly as the hinge position moved to the trailing edge of the airfoil. Using perpendicular suction caused to increase the lift coefficient and decrease the drag coefficient. Consequently, the maximum value of the lift-to-drag ratio (CL/CD) for perpendicular and tangential suctions was achieved about 35.8% and 25.1% higher than that of the case without suction at an angle of attack of 12° and H = 0.9c. Also, the effect of perpendicular suction was more considerable compared to the tangential suction. This caused a reduction in the size of the recirculation zone from 0.5 to 0.09 of the airfoil chord length and also transferred it from 1.13 to 1.18 of the airfoil chord length.

Computational fluid dynamics simulation of aerodynamic performance and flow separation by single element and slatted airfoils under rainfall conditions

Abstract: This study investigated the effects of rainfall on flow separation and the aerodynamic performance of single element and slatted NACA 0012 airfoils by using a mathematical model developed with the commercial computational fluid dynamics solver ANSYS FLUENT 18.2. A two-way momentum coupled Eulerian–Lagrangian multiphase approach was used to simulate the formation of the water film layer on the airfoil's surface. According to the results, very low values of the lift-to-drag ratio at low angles of attack reflected severe degradation of the aerodynamic performance of the airfoil in the presence of water accumulated on its surface. The impact of rain droplets on the leading-edge slat surface led to less water accumulating on the main section of the airfoil. In particular, the maximum water film mass concentrated on the airfoil surface decreased from 15 g to 1 g compared with the single element airfoil. Hence, the thickness of the water film layer was not sufficiently large to significantly affect the aerodynamic coefficients of the slatted airfoil, especially the maximum lift coefficient, compared with the thicker water film layer on the single element airfoil. In addition, the use of slats clearly enhanced the aerodynamic coefficients and increased the stall angle from 13° to 22° in dry conditions, and from 16° to 24° in rainy conditions. Slats also significantly decreased the boundary layer thickness and delayed the separation at higher angles of attack.

Comparative study of flow separation control using suction and blowing over an airfoil with/without flap

Abstract: This study mainly focused on the comparison of the effect of single and simultaneous suction and blowing jets on the aerodynamic performance of an airfoil with/without flap to evaluate the most effective flow control configuration using computational fluid dynamics (CFD) method. Moreover, the effect of applying single and simultaneous jets have been conducted on delaying and controlling the flow separation. The results were obtained using two-dimensional incompressible Unsteady Reynolds-Averaged Navier–Stokes (URANS), and the turbulence was simulated with SST k-ω turbulence model. Also, different parameters including two jet locations (Ljet), three jet velocity ratios (Rjet), three jet angles (θjet) and three flap deflections (δf) were analyzed to find the most effective case of applying flow control jets to delay the boundary layer separation. It was concluded that applying a single suction jet and simultaneous suction and blowing jets on the flapped airfoil was more effective to improve the lift-to-drag ratio (CL/CD) than applying these jets to the without flap case. The maximum value of CL/CD was achieved by single suction jet for the without flap case which was equal to 73.7. The maximum increment of stall angle over the without flap airfoil and flapped airfoil was obtained by applying single suction jet, which increased the stall angle from 14° to 20° and 14° to 16° for the suction angle of −90° and suction velocity ratio of 0.15, respectively.

Performance improvement of a cyclone separator using different shapes of vortex finder under high-temperature operating condition

Abstract: In the present study, the effect of inlet temperature on cyclone performance was numerically investigated based on computational fluid dynamics (CFD) approach. The Eulerian–Lagrangian approach in conjunction with the Reynolds stress transport model was employed to solve the unsteady Reynolds-averaged Navier–Stokes equations. A series of numerical simulations were carried out at a wide temperature range of 293 K to 700 K. Conclusive results indicated that the separation efficiency of cyclone significantly decreased with any increment of inlet temperature due to weaker swirling flow across the cyclone at a higher temperature. In this condition, it is essential to find an impressive way to overcome this negative effect. Hence, four proposed shapes, namely divergent vortex finder and convergent vortex finder (CVF) were designed to use instead of base one under high-temperature operating conditions. The results extracted from CFD simulations demonstrated that the maximum tangential velocity was obtained about 2.2 times of the inlet velocity (v = 11.99 m/s) at T = 700 K for cyclone with CVF 1, while it was predicted 1.9 times of the inlet velocity for a base cyclone. Moreover, other cyclones generated tangential velocities even less than the base cyclone. Higher tangential velocity led to increase the centrifugal force and cyclone separation efficiency. Using CVF 1 instead of a base vortex finder significantly helped the cyclone to collect finer particles. Whereas the separation efficiency enhanced 9.5% for the particle size of 2 µm at T = 700 K and v = 20.18 m/s compared to the base cyclone.

LES Of Atomizing Spray with Stochastic Modeling of Secondary Breakup

Abstract: A stochastic subgrid model for large-eddy simulation of atomizing spray is developed. Following Kolmogorov’s concept of viewing solid particle-breakup as a discrete random process, atomization of liquid blobs at high relative liquid-to-gas velocity is considered in the framework of uncorrelated breakup events, independent of the initial droplet size. Kolmogorov’s discrete model of breakup is rewritten in the form of differential Fokker–Planck equation for the PDF of droplet radii. Along with the Lagrangian tracking of spray dynamics, the size and number density of the newly produced droplets is governed by the evolution of this PDF in the space of droplet-radius. The parameters of the model are obtained dynamically by relating them to the local Weber number with two-way coupling between the gas and liquid phases. Computations of spray are performed for the representative conditions encountered in idealized diesel and gas-turbine engine configurations. A broad spectrum of droplet sizes is obtained at each location with co-existence of large and small droplets. A novel numerical algorithm capable of simultaneously simulating individual droplets as well as a group of droplets with similar properties commonly known as parcels is proposed and compared with standard parcels-approach usually employed in the computations of multiphase flows. The present approach is shown to be computationally efficient and captures the complex fragmentary process of liquid atomization.

Research on aerodynamic performance of a novel dolphin head-shaped bionic airfoil

Abstract: Based on the special streamline profile of the Phocoenoides dalli head, this paper innovatively proposes to transform the NACA 0018 airfoil into a novel airfoil whose leading edge is similar to the streamline profile of the Phocoenoides dalli head, and makes corresponding minor adjustments to this new airfoil according to the dolphin’s motion behavior, and eventually obtains three kinds of dolphin head-shaped new airfoils including the Original Dolphin Airfoil, the Smooth Transition Dolphin Airfoil and the Deflected Dolphin Airfoil. Due to different deflection angles, the Deflected Dolphin Airfoil is then subdivided into five different types. The aerodynamic performances of these three dolphin head-shaped new airfoils as well as the NACA 0018 airfoil are simulated by using the SST k-ω model at Re = 1.6 × 105. The results show that: Compared with the NACA 0018 airfoil, firstly, the aerodynamic performances of three kinds of dolphin head-shaped airfoils are quite different from each other because of the change of the curvature and the radius of the leading edge. Secondly, by comparing the lift and drag coefficients of the Deflected Dolphin Airfoils with five deflection angles, it is speculated that there is an optimal deflection angle for the Deflected Dolphin Airfoil under the conditions of this paper. Eventually, the deflection angle of 24° is found to be the optimal value among these five different deflection angles. The results of this study can provide reference for improving the performance of blade design, such as the rotating mechanical blades, the aeronautical blades, etc.

The role of notch tip shape and radius on deformation mechanisms of 12Cr1MoV steel under impact loading. Part 1. Energy parameters of fracture

Abstract: Impact loading curves and fracture energy of the notched 12Cr1MoV ductile steel specimens are analysed. The qualitative description and quantitative parameters are obtained for major stages of ductile and brittle fracture depending on the shape of the notch and the stress stiffness ahead. It was shown that a zone with enhanced plasticity forms in the vicinity of V-, U- and I-shaped notches at 20 °C testing temperature, giving rise to ductile fracture. The stress stiffness at the notch tip increased with testing temperature reduced to −40 °C. We demonstrated that the size of shear lips on a fracture surface is a quantitative characteristic of fracture. Using this approach, which is close by nature to non-linear fracture mechanics, together with the quantitative description of fracture surfaces, a physical–mechanical scheme of the specimen fracture was suggested for the case of enhanced and localized (constrained) plasticity near the stress concentrator tip.

Effect of Gurney flap on flow separation and aerodynamic performance of an airfoil under rain and icing conditions

Abstract: In the present study, special attention is paid to numerically investigate the aerodynamic performance of the NACA 0012 airfoil under rain and icing conditions with the aim to better understand the severe aerodynamic performance penalties of aircraft in flight. Furthermore, in order to control the flow separation and improve the aerodynamic performance of the airfoil under critical atmospheric conditions, the Gurney flap with different heights is attached to the trailing edge of the airfoil. The simulation is done at a Reynolds number of 3.1 × 105 under different atmospheric conditions including dry, rain, icing and coupling of rain and icing conditions. A two-way momentum coupled Eulerian–Lagrangian multiphase method is used to simulate the process of water film layer formed on the airfoil surface due to rainfall. According to the results, accumulation of water due to rainfall and ice accretion on the airfoil surface inevitably provides notable negative effects on the aerodynamic performance of the airfoil. It is concluded that icing induces a higher aerodynamic degradation than rain due to very intensive ice accretion. The Gurney flap as a passive flow control method with a favorable height for each condition is very beneficial. The maximum increment of the lift-to-drag ratio is achieved by Gurney flap with a height of 0.01 of airfoil chord length for dry and rain conditions and 0.02 of airfoil chord length for icing and coupling of rain and icing conditions, respectively.

Effects of the hinge position and suction on flow separation and aerodynamic performance of the NACA 0012 airfoil

Abstract: In the present study, the effect of hinge position (H) has been numerically investigated to find the appropriate position for improving the aerodynamic performance of the NACA 0012 flapped airfoil. In addition, perpendicular and tangential suctions have been applied to control the flow separation and enhance the aerodynamic performance over the NACA 0012 flapped airfoil at each different hinge positions. The simulations were carried out at a Reynolds number of 5 × 105 (Ma = 0.021) based on two-dimensional incompressible unsteady Reynolds-averaged Navier–Stokes calculations to determine the adequate hinge position. The turbulence was modeled using the shear stress transport k–ω turbulence model. The effect of perpendicular suction (θjet = − 90°) and tangential suction (θjet = − 30°) was computationally studied over NACA 0012 flapped airfoil for five different hinge positions (H = 0.7c, 0.75c, 0.8c, 0.85c and 0.9c) and a flap deflection (δf) of 15°. Based on the results, the hinge position significantly affects the aerodynamic performance of the airfoil. The lift coefficient increased clearly as the hinge position moved to the trailing edge of the airfoil. Using perpendicular suction caused to increase the lift coefficient and decrease the drag coefficient. Consequently, the maximum value of the lift-to-drag ratio (CL/CD) for perpendicular and tangential suctions was achieved about 35.8% and 25.1% higher than that of the case without suction at an angle of attack of 12° and H = 0.9c. Also, the effect of perpendicular suction was more considerable compared to the tangential suction. This caused a reduction in the size of the recirculation zone from 0.5 to 0.09 of the airfoil chord length and also transferred it from 1.13 to 1.18 of the airfoil chord length.