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Experiments in near-field of turbulent jets into a crossflow
, Article Scientia Iranica ; Volume 13, Issue 2 , 2006 , Pages 134-151 ; 10263098 (ISSN) ; Taeibi Rahni, M ; Soltani, M. R ; Sharif University of Technology
Sharif University of Technology
2006
Abstract
Low-speed wind tunnel experiments were conducted to examine the effects of jet exit behavior on the near-field characteristics of jets in crossflow. To better understand this problem, a row of six square jets were perpendicularly injected into the main turbulent flow. The jet-to-crossflow velocity ratios examined were 0.25, 0.5 and 1.0, while the jet spacing to jet diameter was 3.0. No significant temperature differences between the jet and the crossflow were introduced. The analysis of the vertical structure of the transverse jets, including focusing on the jet shear layer and the vorticity dynamics of the exiting jets, is complicated. The vorticity around the circumference of the jets was...
Vortex shedding modes around oscillating non-uniform double heave plates
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; 2020 ; Alvandi, M ; Behzad, M ; Thiagarajan, K. P ; Sharif University of Technology
SAGE Publications Ltd
2020
Abstract
Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total...
Vortex shedding modes around oscillating non-uniform double heave plates
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 235, Issue 2 , 2021 , Pages 558-569 ; 14750902 (ISSN) ; Alvandi, M ; Behzad, M ; Thiagarajan, K. P ; Sharif University of Technology
SAGE Publications Ltd
2021
Abstract
Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total...
Vortex shedding modes around oscillating non-uniform double heave plates
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 235, Issue 2 , 2021 , Pages 558-569 ; 14750902 (ISSN) ; Alvandi, M ; Behzad, M ; Thiagarajan, K. P ; Sharif University of Technology
SAGE Publications Ltd
2021
Abstract
Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total...
Numerical investigation of effects of uniform magnetic field on heat transfer around a sphere
, Article International Journal of Heat and Mass Transfer ; Volume 114 , 2017 , Pages 703-714 ; 00179310 (ISSN) ; Molaei Dehkordi, A ; Abbasi, F ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
In this article, ferrohydrodynamic forced-convection heat transfer from a heated sphere embedded in a ferrofluid in the presence of the uniform external magnetic field has been studied numerically for the first time over a wide range of Reynolds number value, nanoparticle diameter, particle volume fraction, and magnetic field intensity. Despite the uniform external magnetic field applied, the internal magnetic field near the sphere could be nonuniform due to the considerable difference between the relative magnetic permeability of the sphere and the surrounding medium. Kelvin body force arises from this nonuniformity and induces vortexes near the sphere. These vortexes disturb the boundary...
Numerical analysis of wake structure and performance of two oscillatory mechanisms of a foil: Pure pitching and undulating
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 229, Issue 4 , April , 2015 , Pages 376-396 ; 14750902 (ISSN) ; Ebrahimi, M ; Sharif University of Technology
SAGE Publications Ltd
2015
Abstract
There are various propulsion, maneuvering, and stabilization mechanisms in nature, which can provide inspiration for similar mechanisms in man-made vehicles. This study aims to elucidate and compare the propulsive vortical signature and performance of a foil in two important natural mechanisms of pure pitching and undulatory oscillations. Governing equations are solved with a pressure-based finite volume method solver, in an arbitrary Lagrangian-Eulerian framework domain containing a NACA 0012 foil moving with prescribed kinematics. The results show that in a given Reynolds number (Re), the undulating mechanism produces thrust at a higher Strouhal number (St) and with smaller growth slope,...
Comparative numerical analysis of the flow pattern and performance of a foil in flapping and undulating oscillations
, Article Journal of Marine Science and Technology (Japan) ; Volume 20, Issue 2 , June , 2015 , Pages 257-277 ; 09484280 (ISSN) ; Ebrahimi, M ; Sharif University of Technology
Springer-Verlag Tokyo
2015
Abstract
Nature presents a variety of propulsion, maneuvering, and stabilization mechanisms which can be inspired to design and construction of manmade vehicles and the devices involved in them, such as stabilizers or control surfaces. This study aims to elucidate and compare the propulsive vortical signature and performance of a foil in two important natural mechanisms: flapping and undulation. Navier–Stokes equations are solved in an ALE framework domain containing a 2D NACA 0012 foil moving with prescribed kinematics. All simulations are carried out using a pressure-based finite volume method solver. The results of time-averaged inline force versus Strouhal number (St) show that in a given...
Numerical simulation of vortex-induced vibration of a smooth circular cylinder at the subcritical regime
, Article Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment ; Volume 236, Issue 4 , 2022 , Pages 916-937 ; 14750902 (ISSN) ; Nemati Kourabbasloo, N ; Mohtat, P ; Tanha, A ; Sharif University of Technology
SAGE Publications Ltd
2022
Abstract
The present paper focuses on the simulation of vortex-induced vibration (VIV) of a rigid, smooth circular cylinder with elastic supports subject to a cross-flow at the subcritical regime of Reynolds number, 30,000
Two-phase flow separation in axial free vortex flow
, Article Journal of Computational Multiphase Flows ; Volume 9, Issue 3 , 2017 , Pages 105-113 ; 1757482X (ISSN) ; Ganjiazad, R ; Roshandel, R ; Ashjari, M. A ; Sharif University of Technology
Abstract
Multi-phase flows, particularly two-phase flows, are widely used in the industries, hence in order to predict flow regime, pressure drop, heat transfer, and phase change, two-phase flows should be studied more precisely. In the petroleum industry, separation of phases such as water from petroleum is done using rotational flow and vortices; thus, the evolution of the vortex in two-phase flow should be considered. One method of separation requires the flow to enter a long tube in a free vortex. Investigating this requires sufficient knowledge of free vortex flow in a tube. The present study examined the evolution of tube-constrained two-phase free vortex using computational fluid dynamics. The...
Temperature distribution on a gas turbine shaft exposed to swirl combustor flue
, Article Journal of Thermophysics and Heat Transfer ; Volume 29, Issue 2 , 2015 , Pages 319-328 ; 08878722 (ISSN) ; Saidi, M. H ; Mozafari, A. A ; Keshavarz, P ; Sharif University of Technology
Abstract
A gas turbine shaft is generally exposed to high-temperature gases and may seriously be affected and overheated duetotemperature fluctuationsinthe combustion chamber. Vortex flow inthe combustion chamber may increase the heat release rate and combustion efficiency, as well as control the location of energy release. However, this may result in excessive temperature on the combustor equipment and gas turbine shaft. In this study, a new gas turbine combustion chamber implementing a liner around the shaft and the liquid-fuel feeding system is designed and fabricated. The influences of parameters such as the Reynolds number and the equivalence ratio are studied. Experimental results are compared...
Analysis of temperature distribution over a gas turbine shaft exposed to a swirl combustor flue
, Article 2010 14th International Heat Transfer Conference, IHTC 14 ; Volume 5 , 2010 , Pages 183-190 ; 9780791849408 (ISBN) ; Saidi, M. H ; Ghafourian, A ; Mozafari, A. A ; Sharif University of Technology
2010
Abstract
Gas turbine shaft is generally exposed to high temperature gases and may seriously be affected and overheated due to temperature fluctuations in the combustion chamber. Considering vortex flow in the combustion chamber, it may increase the heat release rate and combustion efficiency and also control location of energy release. However, this may result in excess temperature on the combustor equipments and gas turbine shaft. Vortex flow in the vortex engine which is created by the geometry of combustion chamber and conditions of flow field is a bidirectional swirl flow that maintains the chamber wall cool. In this study a new gas turbine combustion chamber implementing a liner around the shaft...
Numerical analysis of coherent structures in bidirectional swirl combustion chamber
, Article Computational Thermal Sciences ; Volume 8, Issue 3 , 2016 , Pages 265-289 ; 19402503 (ISSN) ; Keshavarz, P. M ; Saidi, M. H ; Sharif University of Technology
Begell House Inc
Abstract
Analysis and identification of vortex structures and their formation, particularly in swirl flows, have received widespread interest among researchers in the field of fluid mechanics. Due to the importance of vortex structures and their applications in combustion chambers, a special type of combustion chamber, which is called a “bidirectional swirl combustor,” has been investigated in this work. The dependence of vortex structures on the combustion chamber geometry and fuel injection location in cold flow, the effect of hot flow on coherent structures, and the difference between vortex structures in hot and cold flows have been studied as well. A common characteristic which is in combustion...
Turbulent decaying swirling flow in a pipe
, Article Heat Transfer Research ; Volume 49, Issue 16 , 2018 , Pages 1559-1585 ; 10642285 (ISSN) ; Saidi, M. H ; Sharif University of Technology
Begell House Inc
2018
Abstract
In this work, a solution is applied to investigate the heat transfer characteristics in a pipe with turbulent decaying swirling flow by using the boundary layer integral scheme. The governing equation is solved using the forth-order Runge-Kutta scheme resulting in thermal boundary-layer thickness and dimensionless heat transfer coefficient, namely, the Nusselt number. Both forced- and free-vortex profiles are considered for the tangential velocity component. A comparison of the results obtained for the Nusselt number with available experimental data shows that this scheme has good capability in predicting the heat transfer parameters of swirling flow especially in the entrance region of a...
Prediction of new vortices in single-phase nanofluid due to dipole interaction
, Article Journal of Thermal Analysis and Calorimetry ; Volume 147, Issue 1 , 2022 , Pages 461-475 ; 13886150 (ISSN) ; Cai, J ; Ali, K ; Sharif University of Technology
Springer Science and Business Media B.V
2022
Abstract
Magnetic field effects are encountered in many engineering applications which include but are not limited to metal casting, nuclear reactor coolers, and geothermal energy extraction. On the other hand, due to their outstanding thermal performance, nanofluids have been successful in obtaining acceptability as per the new generation of heat transfer fluids in automotive cooling devices, in heat exchangers, and building heating. Therefore, this research is carried out to understand how the nanofluid flow in a cavity is affected by a magnetic field (due to a dipole placed nearby). The single-phase model is employed for modeling the nanofluid, whereas the governing partial differential equations...
Second-order calibration for the determination of fatty acids in pomegranate seeds by vortex-assisted extraction-dispersive liquid-liquid micro-extraction and gas chromatography-mass spectrometry
, Article RSC Advances ; Volume 5, Issue 15 , 2015 , Pages 11633-11643 ; 20462069 (ISSN) ; Sereshti, H ; Parastar, H ; Sharif University of Technology
Abstract
Multivariate curve resolution-alternating least squares (MCR-ALS) as a second-order calibration algorithm was proposed for the simultaneous analysis of eighteen fatty acid methyl esters (FAMEs) in a standard mixture and pomegranate seed sample using vortex-assisted extraction-dispersive liquid-liquid microextraction (VAE-DLLME), followed by gas chromatography-mass spectrometry (GC-MS). The chemometric resolution, identification and quantification of the target FAMEs in the standard mixture and real sample (i.e., the pomegranate seed) were carried out successfully in the presence of some uncalibrated interferences. The lack of fit (LOF) and reverse match factor (RMF) were used for the...
Imposed magnetic field impact on vortex generation in the laminar nanofluid flow: A computational approach
, Article International Communications in Heat and Mass Transfer ; Volume 139 , 2022 ; 07351933 (ISSN) ; Prakash, M ; Jamshed, W ; Ibrahim, R. W ; Ahmad, S ; Raizah, Z ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
Metal manufacturing plants, nuclear power plants (which produce steam, by using thermal energy yielded during the nuclear fission, for spinning enormous turbines to generate electricity), and geothermal power plants are a few in the extensive list of technologies where different processes occur in high temperature environment in the presence of strong magnetic fields. Nanofluids (NFs), on the other hand, have been successful in achieving wide acceptance as the next generation coolant in the above mentioned industries as well as in the automobiles, heat exchangers, and steam boilers, owing to their remarkable thermal performance. These observations motivate the authors to explore the change...
A liquid film motor
, Article Microfluidics and Nanofluidics ; Volume 6, Issue 5 , 2009 , Pages 711-715 ; 16134982 (ISSN) ; Shirsavar, R ; Hamedani Radja, N ; Ejtehadi, M. R ; Sharif University of Technology
2009
Abstract
It is well known that electro-hydrodynamical effects in freely suspended liquid films can force liquids to flow. Here, we report a purely electrically driven rotation in water and some other liquid suspended films with full control on the velocity and the chirality of the rotating vortices. The device, which is called "film motor", consists of a quasi two-dimensional electrolysis cell in an external in-plane electric field, crossing the mean electrolysis current density. If either the external field or the electrolysis voltage exceeds some threshold (while the other does not vanish), the liquid film begins to rotate. The device works perfectly with both DC and AC fields. © Springer-Verlag...
Geometric optimization of a double pipe heat exchanger with combined vortex generator and twisted tape: A CFD and response surface methodology (RSM) study
, Article Thermal Science and Engineering Progress ; Volume 18 , 2020 ; Amiri, P ; Saffari Pour, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this research, a numerical investigation is done on the effect of employing the new combined vortex generators, the twisted tape turbulator and Al2O3-H2O nanofluid as the involved base fluid. Such study is carried out on the behavior of the heat transfer rate and the pressure drop of a double pipe heat exchanger. Accordingly, the response surface methodology (RSM) grounded on the central composite design (CCD) is used for acquiring the optimized geometry of the combined vortex generator and twisted tape turbulator. In order to have the maximum Nusselt number and minimum friction factor, twenty cases with different pitches ratio Pil=0.09-0.18, angles (θ=0-30°) and Reynolds numbers (Re =...
Wake interference of two identical oscillating cylinders in tandem: An experimental study
, Article Ocean Engineering ; Volume 166 , 2018 , Pages 311-323 ; 00298018 (ISSN) ; Khorasanchi, M ; Day, S ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
This study aims to assess the impact of the spacing between cylinders on their dynamic behaviour. Observations during this experiment have helped to identify the effect of spacing on excitation mechanism of each cylinder as well as establishing the relationship between cylinders response and the spacing between them. Arrays of cylindrical Structures in close proximity are common in variety of engineering structures, particularly in the offshore industry. If the cylinders are flexible, and are subject to excitation from fluid flow, then the dynamics is influenced by complex interactions between the cylinders, dependent on a variety of parameters. Two cylinders were flexibly mounted in tandem...
On the development of a nonlinear time-domain numerical method for describing vortex-induced vibration and wake interference of two cylinders using experimental results
, Article Nonlinear Dynamics ; 2021 ; 0924090X (ISSN) ; Day, S ; Karimirad, M ; Khorasanchi, M ; Sharif University of Technology
Springer Science and Business Media B.V
2021
Abstract
A nonlinear mathematical model is developed in the time domain to simulate the behaviour of two identical flexibly mounted cylinders in tandem while undergoing vortex-induced vibration (VIV). Subsequently, the model is validated and modified against experimental results. Placing an array of bluff bodies in proximity frequently happens in different engineering fields. Chimney stacks, power transmission lines and oil production risers are few engineering structures that may be impacted by VIV. The coinciding of the vibration frequency with the structure natural frequency could have destructive consequences. The main objective of this study is to provide a symplectic and reliable model capable...