Ali Lohrasbi Nichkoohi

Bio: Ali Lohrasbi Nichkoohi is an academic researcher from Islamic Azad University. The author has contributed to research in topics: Airfoil & Lift coefficient. The author has an hindex of 4, co-authored 8 publications receiving 34 citations. Previous affiliations of Ali Lohrasbi Nichkoohi include Amirkabir University of Technology.

Numerical study of the effect of suction at a compressible and high Reynolds number flow to control the flow separation over Naca 2415 airfoil

Abstract: This study focused on delaying and controlling the flow separation over Naca 2415 airfoil by finding the best slot location with the most effective suction velocity ratio and suction angle to apply suction at a compressible and high Reynolds number flow using computational fluid dynamics method. The results were obtained with two dimensional compressible Reynold-averaged Navier-Stokes equations, and the turbulence was simulated with k-e RNG turbulence model. The results indicated that the most effective slot locations for applying suction were between 0.3 to 0.6 of the airfoil chord length. Also, it was found that the maximum value of the lift coefficient was obtained at an angle of attack of 16° on 0.3 of airfoil chord length and suction velocity ratio of 1.5. This value is about 55% compared to the case without suction, and thus the stall angle increased from 10° to 16°.

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.

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.

Experimental and numerical investigations of a modified designed baseboard radiator using an air gap enhancing free convection heat transfer

Abstract: The present study aims to improve the thermal performance of conventional radiant baseboard heating systems by proposing a novel and modified design with the least cost and complexity. The convection to radiation ratio for conventional and modified baseboard designs is compared by several experimental tests and numerical simulations of heat transfer between internal pipe flow and indoor air convective flow. By examining the temperature and velocity profiles of both radiant baseboards, it is revealed that the total thermal power of the modified radiant baseboard is 34% higher than that of the conventional one, especially at the occupied zone which has raised indoor air temperature by up to 2 °C in different resident postures such as standing, sitting and sleeping. Also, the results show that the convection contribution of the modified design of radiant baseboard is greater than the conventional one, more than 45% in the same conditions, while radiation contribution also grows considerably. The results of 3D steady-state numerical simulations show that heat output from the modified radiant baseboard per cm of panel height is 3 times more than that of the conventional one. Consequently, it is indicated that the modified radiant baseboard has a lower supply temperature, leading to energy-space saving, while its capability to overcome cold air down draught flow is more, which can be of interest to experts in the thermal comfort field. Furthermore, by choosing a modified radiant baseboard, the required length of the baseboard will be reduced by 50% compared to the conventional one, and this can have a significant impact on the architectural and economic limitations of the building industry.

Numerical investigation of high pressure and high Reynolds diffusion flame using Large Eddy Simulation

Abstract: Today, with nonstop improvement in computational power, Large-Eddy Simulation (LES) is a high demanding research tool for predicting engineering flows. Such flows on high pressure condition like diesel engines is extensively employed in ground and marine transportation, oblige the designer to control and predict toxic pollutants, while maintaining or improving their high thermal efficiency. This becomes one of the main challenging issues in decades. In the present work, numerical investigation of diffusion flame dynamics is performed in the near-field of high-Reynolds jet flow on high pressure condition encountered in diesel engine applications. This work discusses the implementation of Partially Stirred Reactor (PaSR) combustion model by the approaches of large eddy simulation (LES). The simulation results show that LES, in comparison with Reynolds-Averaged Navier-Stokes (RANS) simulation predicts and captures transient phenomena very well. These phenomena such as unsteadiness and curvature are inherent in the near-field of high Reynolds diffusion flame. The outcomes of this research are compared and validated by other researchers’ results. Detailed comparisons of the statistics show good agreement with the corresponding experiments.

Performance evaluation of ventilation radiators

Abstract: Energy consumption for heating and ventilation of buildings is still in 2011considered far too high, but there are many ways to save energy and construct lowenergy buildings that have not been fully utilised. This doctoral thesis has focused onone of these - low temperature heating systems. Particular attention has been given tothe ventilation radiator adapted for exhaust-ventilated buildings because of itspotential as a low energy consuming, easily-operated, environmentally-friendlysystem that might also ensure occupant health and well-being. Investigations were based on Computational Fluid Dynamics (CFD) simulations andanalytical calculations, with laboratory experiments used for validation. Main conclusions: Low and very low temperature heating systems, such as floor heating, in general createan indoor climate with low air speeds and low temperature differences in the room, whichis beneficial for thermal comfort. A typical disadvantage, however, was found to beweakness in counteracting cold down-flow from ventilation air supply units in exhaustventilatedbuildings. with ventilation radiators, unlike most other low temperature systems, it was found thatthe risk of cold draught could be reduced while still maintaining a high ventilation rateeven in cold northern European winters. ventilation radiators were found to be more thermally efficient than traditional radiators. design of ventilation radiators could be further modified for improved thermal efficiency. at an outdoor temperature of -15 °C the most efficient models were able to give doublethe heat output of traditional radiators. Also, by substituting the most efficient ventilationradiators for traditional radiators operating at 55 °C supply water temperature, it wasfound that supply water temperature could be reduced to 35 °C while heat outputremained the same and comfort criteria were met. lowering the supply water temperature by 20 °C (as described above) could givecombined energy savings for heating and ventilation of 14-30 % in a system utilising aheat pump. supply water temperatures as low as 35 °C could increase potential for utilising lowtemperature heat sources such as sun-, ground-, water- or waste-heat. This would beparticularly relevant to new-built “green” energy-efficient buildings, but severaladvantages may apply to retrofit applications as well. Successful application of ventilation radiators requires understanding of relevant buildingfactors, and the appropriate number, positioning and size of radiators for best effect.Evaluation studies must be made at the level of the building as a whole, not just for theheating-ventilation system. This work demonstrated that increased use of well-designed ventilation radiatorarrangements can help to meet regulations issued in 2008 by the Swedish Departmentof Housing (Boverket BBR 16) and goals set in the Energy Performance of BuildingsDirective (EPBD) in the same year.

Improving the hydrodynamic performance of the SUBOFF bare hull model: a CFD approach

Abstract: The main aims of this study are to investigate the hydrodynamic performance of an autonomous underwater vehicle (AUV), calculate its hydrodynamic coefficients, and consider the flow characteristics of underwater bodies. In addition, three important parts of the SUBOFF bare hull, namely the main body, nose, and tail, are modified and redesigned to improve its hydrodynamic performance. A three-dimensional (3D) simulation is carried out using the computational fluid dynamics (CFD) method. To simulate turbulence, the k–ω shear stress transport (SST) model is employed, due to its good prediction capability at reasonable computational cost. Considering the effects of the length-to-diameter ratio (LTDR) and the nose and tail shapes on the hydrodynamic coefficients, it is concluded that a hull shape with bullet nose and sharp tail with LTDR equal to 7.14 performs better than the SUBOFF model. The final proposed model shows lower drag by about 14.9% at u = 1.5 m·s−1. Moreover, it produces 8 times more lift than the SUBOFF model at u = 6.1 m·s−1. These effects are due to the attachment of the fluid flow at the tail area of the hull, which weakens the wake region.

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.

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.