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Experimental study of flow field on stepped airfoil at very low Reynolds number
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 231, Issue 9 , 2017 , Pages 1706-1717 ; 09544100 (ISSN) ; Ghassemi, H ; Ebrahimi, A ; Ghasemi, B ; Sharif University of Technology
Abstract
In this article, the flow field around NACA0024 airfoil with step at lower and upper surfaces is experimentally investigated. For this purpose, particle image velocimetry technique based on the instantaneous flow structures is used to investigate the flow field around the airfoil at different times. All the experimental measurements in current study are conducted at very low Reynolds number condition based on the chord of the airfoil (Re=2000) and at angles of attack at 0° and 5° where the flow around airfoils is separated. The differences between vortical structures, mean streamlines, sizes of the wake regions, and vortex shedding of the stepped airfoils compared to unmodified airfoil are...
Numerical study on boundary layer control using CH4[sbnd]H2[sbnd]air Micro-reacting jet
, Article International Journal of Hydrogen Energy ; Volume 41, Issue 47 , 2016 , Pages 22433-22452 ; 03603199 (ISSN) ; Yahyavi Koochaksarai, M ; Javadi, K ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
The focus of present numerical study is on assessment of control of laminar separation bubble phenomenon using Micro-scale combustion actuators in an airfoil with low Reynolds number under surface effect and free flows. In this way, the characteristics of laminar separation bubble such as its formation, geometry, and transition from laminar to turbulent around airfoil SD8020 in attack angles of 5 and 8° are investigated. Following that, the new combustion actuators in Micro-scale, cold, and hot air-jet injection are introduced to control boundary layer flow in terms of eliminating the separation bubble. Some mechanisms are identified for improvement of methane-air premixed flame...
Design and Dynamical Modelling and Control of a Micro-swimmer with High Maneuverability
, M.Sc. Thesis Sharif University of Technology ; Nejat, Hossein (Supervisor) ; Meghdari, Ali (Supervisor)
Abstract
Up to now many different mechanisms have been proposed for a swimming micro robot, but most of the previously designed micro robots are not able to perform three- dimensional maneuver and the motion of the proposed swimmers are limited along a straight line or in a plane. Some important issues that must be ruled in designing micro robots include: reduced number of actuators, high maneuverability, high motion controllability and elimination of lateral drift. In this study the aim is to design a micro swimmer with the aforementioned capabilities as much as possible. In this regard, many different ideas based on the quadrotor motion, flagellated bacteria and spiral flagellated bacteria, Fish...
Designing and Developing an Active Micromixer Based on Optical Tweezers for Microfluidics
, M.Sc. Thesis Sharif University of Technology ; Seyed Reihani, Nader (Supervisor)
Abstract
Microfluidics is a field of science that studies micron-scale characteristics of fluids. In this scale fluids show fascinating behavior far beyond our expectation compared to their large-scale counterparts. One of such peculiar behavior is the mixing of two different liquids flowing inside a microchannel. Due to low Reynolds number, the flow inside such a channel would be dominated by laminar behavior. In this regime mixing of the fluids is only mediated by molecular diffusion which is a rather slow process. In the current thesis, we utilized the rotating ability of optical tweezers to construct an active micromixer for Microfluidics. In order to do this we used birefringent microbeads. The...
The Experimental Investigation of Lateral Dispersion In Vegetated Flow
, M.Sc. Thesis Sharif University of Technology ; Jamali, Mirmosadegh (Supervisor)
Abstract
There is an importance issue for preservation and survival of ecological systems by vegetation. A study focusing on the hydrodynamics of these complex ecosystems could help to explain the filtering ability of vegetation in wetlands and estuaries. Wetlands assist in flood control, shoreline protection, and groundwater recharge.In addition, they play a purification role, removing sediments and contaminants from polluted waters, nutrient uptake, and oxygen production. Laboratory experiments have been designed to study the influence of marsh vegetation on lateral dispersion. The flow through vegetation is modeled by a circulating flow going through an array of plastic dowels in an experimental...
, M.Sc. Thesis Sharif University of Technology ; Jamali, Mirmossadegh (Supervisor)
Abstract
Preservation and survival of ecological systems by vegetation is important. A study focusing on the hydrodynamics of these complex ecosystems could help to explain the filtering ability of vegetation in wetlands and estuaries. Wetlands assist in flood control, shoreline protection, and groundwater recharge. In addition, they play a purification role in removing sediments and contaminants from polluted waters, nutrient uptake, and oxygen production.
Laboratory experiments have been designed to study the influence of marsh vegetation on lateral dispersion in flexible vegetation that has been modelled with inclined cylinder. The flow through vegetation is modelled by a circulating flow...
Laboratory experiments have been designed to study the influence of marsh vegetation on lateral dispersion in flexible vegetation that has been modelled with inclined cylinder. The flow through vegetation is modelled by a circulating flow...
Simulation of Mass Transfer from Droplet in a Two Phase Liquid-liquid Extraction System
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Firoozabadi, Bahar (Co-Advisor)
Abstract
Mass transfer of a drop moving in a bulk fluid is an interesting subject which has attracted a lot of attention. Understanding effective parameters in this process would be helpful in order to increase the efficiency of the industrial processes related to mass transfer. In this research, the deformation and mas transfer of a moving drop was studied numerically. Navier-Stokes equations and concentration equation were solved separately with a VOF method in an axisymmetric domain using Fluent software. Comparision between numerical results and former experimental results proves the accuracy of the modelling in both fields of deformation and mass transfer. Moreover, effects of the physical...
Simulation of Drag Reduction Via Microgrooves
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor)
Abstract
Drag reduction on surfaces always has been a great case of study, especially in transport industry. This project discusses the external laminar flow of a single-phase fluid over a flat plate and the effects of making rectangular tiny grooves - in micron or millimeter - on them to reduce total drag. Making grooves with appropriate geometry on surfaces causes the fluid-solid contact area on the groove's surface turn into fluid-fluid and as a result the fluid will not shed into the groove. In other words the flow instead of having a no-slip boundary condition on inner surfaces of the groove, creates vortices in them that causes a remarkable reduction in velocity gradient followed by a skin...
Video images and undulatory movement equation of pangasius sanitwongsei's caudal fin of steady swimming fish
, Article International Journal of Design and Nature and Ecodynamics ; Vol. 9, issue. 2 , 2014 , pp. 95-108 ; ISSN: 1755-7445 ; Abbaspour, M ; Sharif University of Technology
Abstract
Experimental hydrodynamics imaging of four Pangasius sanitwongsei were considered. A quantitative characterization of caudal fin is presented in this article. Steady swimming of four P. sanitwongsei with different total length was studied experimentally and taped by high-speed digital video, and undulatory movement of each fish at different velocity was revealed. The pattern of body undulatory movement of the fish was drawn from the video images. Three main factors that determine the fish swimming behavior are Reynolds number, Strouhal number and shape. In this study, Lf/L was chosen as a characteristic of shape, where Lf was the distance from the start of the head to the end of the head....
Modeling active micromixers with multiple microstirrers using smoothed particle hydrodynamics
, Article Scientia Iranica ; Vol. 21, issue. 4 , 2014 , pp. 1390-1402 ; ISSN: 10263098 ; Pishevar, A ; Saidi, M. S ; Sharif University of Technology
Abstract
The smoothed particle hydrodynamics method is used to explore the effects of design parameters on the mixing efficiency of two types of active micromixer. First, the complex flow field and the mixing process of two separated fluids in a square mixing chamber with nine symmetric microstirrers are simulated. The influence of design parameters, such as the microstirrer rotation arrangement and the angular velocity of the microstirrer, on the mixing performance, is investigated. The mixing index parameter on ten control points is calculated and the average mixing index is compared for different cases. Simulations illustrate that the rotation arrangement of microstirrers is a key parameter in the...
Stochastic nature of series of waiting times
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 87, Issue 6 , 2013 ; 15393755 (ISSN) ; Aghamohammadi, C ; Dashti Naserabadi, H ; Salehi, E ; Behjat, E ; Qorbani, M ; Khazaei Nezhad, M ; Zirak, M ; Hadjihosseini, A ; Peinke, J ; Tabar, M. R. R ; Sharif University of Technology
2013
Abstract
Although fluctuations in the waiting time series have been studied for a long time, some important issues such as its long-range memory and its stochastic features in the presence of nonstationarity have so far remained unstudied. Here we find that the "waiting times" series for a given increment level have long-range correlations with Hurst exponents belonging to the interval 1/2
Numerical investigation on the effect of the size and number of stages on the tesla microvalve efficiency
, Article Journal of Mechanics ; Volume 29, Issue 3 , 2012 , Pages 527-534 ; 17277191 (ISSN) ; Kolahdouz, E. M ; Shirani, E ; Shafii, M. B ; Sharif University of Technology
2012
Abstract
In the present study, the effect of the number of stages of Tesla Micro-Valve (TMV), as well as the dependency of Reynolds number, Re, on the valve performance has been analyzed. For this purpose, different layouts include one to four-stage with different sizes are investigated numerically. The main criterion for evaluation of valves performance is diodicity, Di. Unsteady and steady flow in valve have been simulated and compared. It is shown that although there are some difference but the trend is similar for both responses. Finally, 2-D and steady state computations of the fluid flow have been utilized that reveal a strong dependence of Di on Re and pressure drop, ΔP. The results showed...
Effects of cylinder diameters, reynolds number and distance between two-tandem cylinders on the wake profile and turbulence intensity
, Article ASME-JSME-KSME 2011 Joint Fluids Engineering Conference, AJK 2011 ; Volume 1, Issue PARTS A, B, C, D , 2011 , Pages 3441-3447 ; 9780791844403 (ISBN) ; Jafarian, M. M ; Khoshnevis, A ; Sharif University of Technology
Abstract
A series of experimental and numerical investigations on two tandem cylinders wake have been studied. The velocity profile and turbulence intensity have been acquired by a single one dimensional Hot Wire anemometer. The two cylinders were mounted in a tandem manner in the horizontal mid plane of the working section. The effect of the upstream cylinder diameter, Reynolds number and the distance between the cylinders on the wake profile and turbulence intensity on the downstream cylinder was investigated, while the Reynolds number ranged between1.5× (10)∧4 ∼ 3×(10)∧4. The upstream cylinder diameter (d) was 10, 20 and 25 mm, while the downstream cylinder diameter (D) was 25 mm, corresponding to...
SPH simulation of interacting solid bodies suspended in a shear flow of an Oldroyd-B fluid
, Article Journal of Non-Newtonian Fluid Mechanics ; Volume 166, Issue 21-22 , November , 2011 , Pages 1239-1252 ; 03770257 (ISSN) ; Fatehi, R ; Manzari, M. T ; Sharif University of Technology
2011
Abstract
An explicit weakly compressible SPH method is introduced to study movement of suspended solid bodies in Oldroyd-B fluid flows. The proposed formulation does not need further stabilizing treatments and can be efficiently employed to study particulate flows with Deborah to Reynolds number ratios up to around 10. A modified boundary treatment technique is also presented which helps to deal with the movement of solid particles in the flow. The technique is computationally efficient and gives an improved evaluation of fluid-solid interaction forces.A number of test cases are solved to show performance of the proposed method in simulating particulate viscoelastic flows containing circular and...
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,...
Experimental study of parameters affecting the nusselt number of generator rotor and stator
, Article Heat Transfer Engineering ; Volume 31, Issue 3 , 2010 , Pages 243-249 ; 01457632 (ISSN) ; Nili Ahmadabadi, M ; Hashemi, A ; Sharif University of Technology
2010
Abstract
In this research, the parameters affecting the Nusselt number of a generator rotor and stator under varying heat transfer rate are experimentally studied. In spite of the stator having no grooves, the rotor has four large triangular grooves. The temperature and then heat transfer rate of the rotor and stator are experimentally measured in three longitudinal and two angular positions. First, the effect of axial Reynolds number and rotor rotational speed on the rotor and stator Nusselt number with constant heat transfer rate ratio is studied. The range of the axial Reynolds number and rotational speed used is from 4000 to 30,000 and from 300 to 1500 rpm, respectively. Next, the effect of...
Numerical modeling of ureagenesis in a microfluidic channel mimicking a liver lobule
, Article 2015 22nd Iranian Conference on Biomedical Engineering, ICBME 2015, 25 November 2015 through 28 November 2015 ; 2015 , Pages 54-59 ; 9781467393515 (ISBN) ; Firoozabadi, B ; Saidi, M. S ; Firoozbakhsh, K ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
Ammonia detoxification is one of the main functions of the liver results in production of urea. In this study ammonia elimination and urea production was simulated in a microchannel mimicking the hepatic porto central axis. Navier- Stockes equations along with convection equations were solved for the related species in the entire domain. Since the Reynolds number was small (~1) the fluid flow regime was laminar. Urea cycle was modeled regarding its four main enzymes. Twelve rate equations were also solved in order to obtain the concentration of each metabolites participating in urea cycle. Concentration of the urea reached its maximum ca. 1.2e-5 M at the end of the channel which is in good...
Numerical investigation of wall curvature effects on heat transfer and film cooling effectiveness
, Article Heat Transfer Research ; Volume 47, Issue 6 , 2016 , Pages 559-574 ; 10642285 (ISSN) ; Taiebi Rahni, M ; Xie, G ; Asadi, M ; Sharif University of Technology
Begell House Inc
2016
Abstract
In this research, the problems of adiabatic film-cooling the flat, convex, and concave surfaces are investigated numerically. Two different radii of curvature and one row of vertical injection holes are considered. The Navier-Stokes equations are solved using a fine nonuniform multiblock staggered curvilinear grid and the SIMPLE-based finite volume method. The blowing rates are 0.5 and 1.0 and the mainstream Reynolds number is 10,000. The obtained results indicated that at a low blowing ratio, the cooling effectiveness enhances over the convex surface and reduces over the concave surface compared to the flat surface case. In comparison with the low blowing ratio, the curvature effects at a...
Numerical simulations of turbulent flow around side-by-side circular piles with different spacing ratios
, Article International Journal of River Basin Management ; Volume 15, Issue 2 , 2017 , Pages 227-238 ; 15715124 (ISSN) ; Ataie Ashtiani, B ; Dashtpeyma, H ; Sharif University of Technology
Taylor and Francis Ltd
2017
Abstract
Numerical simulations of the turbulent flow around single and side-by-side piles at different spacing ratios (centre-to-centre distance to the pile diameter) with flow Reynolds number of 105 on the fixed flat-bed are presented. The calculations are performed using the computational fluid dynamics model, FLOW-3D, which solves the Navier–Stokes equations in three dimensions with a finite-volume method. The numerical results of time-averaged flow patterns around single and side-by-side piles are validated using the available experimental measurements. At the downstream of the single pile, dimensionless vortex shedding frequency (Strouhal number) is estimated as 0.22. The maximum values of bed...
Using approximate similitude to design dynamic similar models
, Article Aerospace Science and Technology ; Volume 94 , 2019 ; 12709638 (ISSN) ; Hajipouzadeh, P ; Sharif University of Technology
Elsevier Masson SAS
2019
Abstract
This research deals with the analysis of approximate similitude between the dynamic similar models and the full-scale prototype of an aircraft. Due to physical and technical constraints, a full dynamic similarity is not practically possible and previous works have all neglected one or two similarity criteria like Mach or Reynolds numbers for the sake of Froude number similarity. In this work, it is shown that Mach number has an important effect on aerodynamic characteristics and dynamic response of an aircraft and that neglecting it makes the generalization of the scale-model test data invalid for the full-scale prototype. In order to address this problem, a measurable quantity named...