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Neural network prediction of a liquid-liquid coaxial swirl injector performance map
, Article 43rd AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 10 January 2005 through 13 January 2005 ; 2005 , Pages 11401-11408 ; Soltani, M. R ; Morad, M. R ; Ashjaee, M ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2005
Abstract
A general regression neural network technique is applied for design optimization of liquid-liquid coaxial swirl injectors. Phase Doppler Anemometry measurements for velocity and SMD distributions for various Reynolds numbers are used to train the neural network to generate the injector's performance map. Excellent agreement between the predicted values and the measurements is obtained. It is observed that by reducing the number of randomly selected training samples to about one third of the number of prediction points, one may reconstruct the velocity field in the extrapolation regime with an accuracy of 93%. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc....
Transient and stability analysis in single-phase natural circulation
, Article Annals of Nuclear Energy ; Volume 31, Issue 10 , 2004 , Pages 1177-1198 ; 03064549 (ISSN) ; Misale, M ; D'Auria, F ; Salehi, M. A ; Sharif University of Technology
2004
Abstract
This paper presents the mathematical modeling of single-phase natural circulation of the University of Genoa's rectangular loop (LOOP#1) by a computer program and using RELAP5 system code. The mass, momentum and energy conservation equations in transient form were solved numerically using the finite difference method. One-dimensional linear stability analysis was performed for the single-phase natural circulation loop and the numerical perturbation technique was used in this analysis. The Nyquist criterion was employed to find the stability map of the LOOP#1. The obtained transient results using the first order upwind scheme of the fluid temperatures in various sectors of the LOOP#1 are...
Performance calculations within the conceptual design process of hand-launched aircraft
, Article Applied Mechanics and Materials ; Vol. 629, issue , October , 2014 , p. 145-151 ; Banazadeh, A ; Sharif University of Technology
Abstract
Matching diagram is a key part of the conceptual design process to determine the wing area and the required power. However, it requires drag polar estimation and the assumption of maximum lift coefficient. In case of conventional manned aircraft, early estimation techniques are based on statistical data that are not suitable for hand-launched aircraft. In this study, it has been attempted to present the performance calculations and a proper conceptual design model by acquiring sound values for the aerodynamic coefficients in low Reynolds number, using statistical wetted area as well as a raw design of fuselage, wing and tails. The process is applied to a sample scenario and the results are...
An experimental investigation of transition point over a quasi-2D swept wing by using hot film
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 229, Issue 2 , February , 2015 , Pages 243-255 ; 09544100 (ISSN) ; Soltani, M. R ; Masdari, M ; Davari, A ; Sharif University of Technology
SAGE Publications Ltd
2015
Abstract
In this study, we performed experiments to investigate the effect of sweep angle on the transition location of laminar flow to turbulent flow. Three half wing models were used, each having a different sweep angle but with the same aspect ratio in various angles of attack. Two flat plates were used at the ends of the swept wing models to prevent the flow from rolling up over the wing. By simulating flow over infinity swept wing by eliminating tip vertices, the effect of sweep angle on flow transition phenomenon was investigated. The experiments included the study of transition flow via hot-film sensors, which were glued on the wing surface. We found that the small leading-edge radius and low...
Numerical investigation of the inlet baffle, header geometry, and triangular fins effects on plate-fin heat exchangers performance
, Article Heat Transfer Engineering ; Volume 36, Issue 16 , 2015 , Pages 1397-1408 ; 01457632 (ISSN) ; Afshin, H ; Farhanieh, B ; Sharif University of Technology
Taylor and Francis Ltd
2015
Abstract
In this study, the optimal location of baffle in the header of air-to-air plate heat exchangers and the geometry of the header and the effects of triangular fins arrays on the effectiveness were numerically investigated for different flow rates and Reynolds numbers on different models. The main purpose of inlet baffle and geometry changes is to improve the pattern of flow distribution and assist flow uniformity. The investigations show that the optimal location of the inlet baffle with high Reynolds numbers has an insignificant effect on effectiveness, while with Reynolds numbers 250-3000, the effectiveness is affected significantly by baffle location. On the other hand, the reduction in...
Numerical study of external flow over ducts with various cross-sections
, Article Defect and Diffusion Forum ; Volume 366 , 2016 , Pages 10-16 ; 10120386 (ISSN) ; Sadrhosseini, H ; Sharif University of Technology
Trans Tech Publications Ltd
Abstract
In this article a comprehensive numerical study is performed to compare the effect of fluid flow across a duct with various cross sectional shapes and with different velocities of the flow. Circular, elliptical and rectangular cross sections have been chosen for the ducts and air flows across them with four values of low Reynolds numbers in the range of Re = 1 to Re = 1000. Continuity and momentum equations with proper boundary conditions are solved in two dimensions. Streamlines, pressure distribution and Velocity profiles are obtained and creation of vortices, boundary layers, separation region, wake region, reattachment point and stagnation points are studied in detail and the results are...
Dynamo effect and turbulence in hydrodynamic weyl metals
, Article Physical Review Letters ; Volume 121, Issue 17 , 2018 ; 00319007 (ISSN) ; Kargarian, M ; Syzranov, S ; Sharif University of Technology
American Physical Society
2018
Abstract
The dynamo effect is a class of macroscopic phenomena responsible for generating and maintaining magnetic fields in astrophysical bodies. It hinges on the hydrodynamic three-dimensional motion of conducting gases and plasmas that achieve high hydrodynamic and/or magnetic Reynolds numbers due to the large length scales involved. The existing laboratory experiments modeling dynamos are challenging and involve large apparatuses containing conducting fluids subject to fast helical flows. Here we propose that electronic solid-state materials - in particular, hydrodynamic metals - may serve as an alternative platform to observe some aspects of the dynamo effect. Motivated by recent experimental...
A new insight into onset of inertial flow in porous media using network modeling with converging/diverging pores
, Article Computational Geosciences ; Volume 22, Issue 1 , February , 2018 , Pages 329-346 ; 14200597 (ISSN) ; Hassani, A. H ; Ghazanfari, M. H ; Sharif University of technology
Springer International Publishing
2018
Abstract
The network modeling approach is applied to provide a new insight into the onset of non-Darcy flow through porous media. The analytical solutions of one-dimensional Navier-Stokes equation in sinusoidal and conical converging/diverging throats are used to calculate the pressure drop/flow rate responses in the capillaries of the network. The analysis of flow in a single pore revealed that there are two different regions for the flow coefficient ratio as a function of the aspect ratio. It is found that the critical Reynolds number strongly depends on the pore geometrical properties including throat length, average aspect ratio, and average coordination number of the porous media, and an...
Simulation of compressible and incompressible flows through planar and axisymmetric abrupt expansions
, Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 141, Issue 11 , 2019 ; 00982202 (ISSN) ; Shafiei Ghazani, A ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2019
Abstract
In this paper, compressible and incompressible flows through planar and axisymmetric sudden expansion channels are investigated numerically. Both laminar and turbulent flows are taken into consideration. Proper preconditioning in conjunction with a second-order accurate advection upstream splitting method (AUSM+-up) is employed. General equations for the loss coefficient and pressure ratio as a function of expansion ratio, Reynolds number, and the inlet Mach number are obtained. It is found that the reattachment length increases by increasing the Reynolds number. Changing the flow regime to turbulent results in a decreased reattachment length. Reattachment length increases slightly with a...
The effects of different jet velocities and axial misalignment on the liquid sheet of two colliding jets
, Article Chemical Engineering Science ; Volume 206 , 2019 , Pages 235-248 ; 00092509 (ISSN) ; Kebriaee, A ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This experimental study investigated the patterns and characteristics of the liquid sheet formed by two axial misaligned colliding jets and two colliding jets with different velocities. The tests were limited to the low Reynolds number region, 100
Shooting at the nanoscale: Collection and acceleration of nanowires with an external electric field
, Article Applied Physics Letters ; Volume 114, Issue 1 , 2019 ; 00036951 (ISSN) ; Esfandiar, A ; Moshfegh, A. Z ; Sharif University of Technology
American Institute of Physics Inc
2019
Abstract
We report an approach for collecting, charging, and exceedingly fast motion of silver nanowires (Ag NWs) using an external static electric field. With a proper choice of suspension medium, dispersed Ag NWs can be efficiently driven to align and accumulate vertically on the edges of two parallel gold microelectrodes on a glass substrate surface by dielectrophoresis. Then, at sufficiently high electric fields (> 2.0 × 10 5 V/m), these NWs break at the electrode contact point while carrying some net charge. Afterwards, they immediately accelerate in the field direction and, despite an extremely low Reynolds number for the motion of NWs in viscous liquids, move with high speeds (> 25 mm/s)...
Experimental study of continuous h2/air rotating detonations
, Article Combustion Science and Technology ; 2020 ; Fahim, M ; Farshchi, M ; Sharif University of Technology
Taylor and Francis Inc
2020
Abstract
An experimental study of a lab scale rotating detonation combustor (RDC) has been conducted to identify and classify its modes of operation under different feeding conditions. The chamber uses air as oxidizer and hydrogen as fuel. The stability diagram of the RDC has been determined based on the detonation chamber Reynolds number and reactants mixture equivalence ratio values. The Reynolds number is based on the air volume flow rate, chamber annulus size, and the reactants mixture feeding slot area. Hence the effects of geometrical parameters and operational parameters on the detonation wave stability can be presented in a single stability map. This diagram identifies different zones in...
Effect of active feather length on aerodynamic performance of airfoils at low reynolds number flow
, Article AIAA AVIATION 2020 FORUM, 15 June 2020 through 19 June 2020 ; Volume 1 PartF , 2020 ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc, AIAA
2020
Abstract
To increase the flight endurance of a Micro air vehicle (MAVs), which operates at low Reynolds number flow, one way is to harvest energy during its flight. By inspiring from the nature when all the birds use their feathers to control and distribute their power along the flying time, a solution might be design of a piezoelectric plate as feathers, which scavenges energy directly from the fluid flow. Cantilevered beam with piezo-ceramic layer undergoing vortex-induced vibrations can convert the mechanical energy available from the ambient environment to a usable electrical power. Since a flow-driven piezoelectric composite beam takes a form of natural three-way coupling of the turbulent fluid...
3-D simulation of sedimentation in turbidity currents
, Article ASME 2007 International Mechanical Engineering Congress and Exposition, IMECE 2007, 11 November 2007 through 15 November 2007 ; Volume 8 , 2007 , Pages 503-517 ; 0791843025 (ISBN) ; Firoozabadi, B ; Ghasvari Jahromi, H ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2007
Abstract
The gravity currents on the inclined boundaries are formed when the inflow fluid has a density difference with the ambient fluid and a tangential component of gravity becomes the driving force. If the density difference arises from the suspended particles, the currents are known as particle-laden density currents, or turbidity currents in which the local density depends on the concentration of particles. A low Reynolds k- Turbulent model is used to simulate three dimensional turbidity currents. Also some laboratory tests were conducted to study the 3D flow resulting from the release of particle laden density currents on a sloping surface in a channel of freshwater via a sluice gate. Kaolin...
Investigation of flow dynamics in porous media using computer simulation
, Article 20th European Simulation and Modelling Conference, ESM 2006, Toulouse, 23 October 2006 through 25 October 2006 ; 2006 , Pages 157-163 ; Zamankhan, P ; Mousavi, S. M ; Pietarinen, K ; Sarkomaa, P ; Sharif University of Technology
EUROSIS
2006
Abstract
The aim of this work is to investigate flow hydrodynamics in porous media. Random non-overlapping spherical particles in a cylindrical geometry were produced as a porous media. Navier-Stokes equations in three-dimensional porous packed bed have been solved and dimensionless pressure drop has been studied for a fluid flow through the porous media at different Reynolds numbers (based on pore permeability and interstitial fluid velocity). The numerical results are in good agreement with those reported by Macdonald (1979) in the range of Reynolds numbers studied. At higher Reynolds numbers turbulent models such as large eddy simulation (LES) and Reynolds stress model (RSM) also have been...
Controlled swarm motion of self-propelled microswimmers for energy saving
, Article Journal of Micro-Bio Robotics ; 2021 ; 21946418 (ISSN) ; Nejat Pishkenari, H ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
Swarm motion is an amazing collective behavior in nature for energy saving. Inspiring this natural phenomenon in microorganisms’ swimming, we have proposed a motion strategy for a swarm of microrobots to reduce their energy consumption during path tracking. The investigated microrobot is an artificial Self-Propelled Microswimmer (SPM) with high maneuverability at low Reynolds number flow (Re ≪ 1). In this study, we have demonstrated that forming a swarm behavior with minimum energy consumption requires the microswimmers to be close enough to each other, since at small distances the hydrodynamic interactions of microswimmers reduce their energy consumption. Moreover, we also showed that...
Investigation of time-frequency analysis and transitional boundary layer over a pitching airfoil
, Article Scientia Iranica ; Volume 28, Issue 2 B , 2021 , Pages 860-876 ; 10263098 (ISSN) ; Soltani, M. R ; Maghrebi, M. J ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2:7 × 105) is experimentally investigated using space-frequency and time-frequency analyses of hot- film signals. Boundary layer events are visualized based on the space-frequency and time-frequency plots. The precursor phenomenon for turbulent and fully separated flows is presented based on the time-frequency analysis. A new technique based on time-frequency analysis of hot- film signals is introduced to measure the transition onset and relaminarization locations. This technique functions based on the analysis of high-frequency disturbances of the measured data. Significant attention has been drawn to the...
Controlled swarm motion of self-propelled microswimmers for energy saving
, Article Journal of Micro-Bio Robotics ; 2021 ; 21946418 (ISSN) ; Nejat Pishkenari, H ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
Swarm motion is an amazing collective behavior in nature for energy saving. Inspiring this natural phenomenon in microorganisms’ swimming, we have proposed a motion strategy for a swarm of microrobots to reduce their energy consumption during path tracking. The investigated microrobot is an artificial Self-Propelled Microswimmer (SPM) with high maneuverability at low Reynolds number flow (Re ≪ 1). In this study, we have demonstrated that forming a swarm behavior with minimum energy consumption requires the microswimmers to be close enough to each other, since at small distances the hydrodynamic interactions of microswimmers reduce their energy consumption. Moreover, we also showed that...
Cost-effective 3D H-filter fabricated by xurographic method
, Article Microfluidics and Nanofluidics ; Volume 26, Issue 9 , 2022 ; 16134982 (ISSN) ; Mirzaei, A ; Taghipoor, M ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2022
Abstract
In this paper, the conventional 2D H-filter is modified to 3D multi-layer structures fabricated by low-cost xurography. The extraction efficiency was studied experimentally for different 3D structures and then compared with conventional 2D H-filter. Numerical simulations were performed to model the diffusion flow in the proposed H-filters, showing a good agreement with the experimental observations. Results show that 3D H-filters have higher extraction efficiency at the same Reynolds number. Moreover, these structures could benefit low-cost and commercial applications due to their higher efficiency at smaller sizes. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH...
Toward the feasible solution of a long-lasting dynamic similitude problem
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; 2022 ; 09544100 (ISSN) ; Banazadeh, A ; Sharif University of Technology
SAGE Publications Ltd
2022
Abstract
Dynamic similar models are designed to study the flight behavior of the full-scale aircraft in early design stages. Due to physical and operational constraints, full dynamic similarity between the scaled-down model and full-scale aircraft is not feasible. Thus, the scale model would be flying at different Reynolds number and Mach number. A given aircraft configuration with specific aerodynamic characteristics will have different performance if Mach number and Reynolds number are changed considerably, which results in different dynamic behavior of the scale model. To compensate for these dissimilarities, it is proposed to modify the airfoil geometry of the scale model to preserve aerodynamic...