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Thermal study of the internal flow in a circular tube with vibrational ball turbulators
, Article International Journal of Heat and Mass Transfer ; Volume 196 , 2022 ; 00179310 (ISSN) ; Aghlichanche, A ; Ataelahi, A ; Mohammadi, O ; Shafii, M. B ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
Flow turbulators have promising heat transfer applications. Here, the novel design proposed in our previous study (vibrational ball turbulators, VBTs, mounted on an elastic wire inside a circular tube) is investigated experimentally from heat transfer and thermal performance standpoints. The effects of diameter (Y) and longitudinal distance (pitch, X) ratios of VBTs, the Reynolds number, and the axial tension of the wire (σ0) on the average Nusselt number (Nu), the average Nusselt number ratio (Nu divided by that of a plain tube, Nup), the friction factor ratio (f/fp), and a parameter called the thermal performance factor (η=(Nu/Nup)/(f/fp)1/3) are studied. Different ball diameter (Y=0.3,...
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...
Investigation of flame structure and precessing vortex core instability of a gas turbine model combustor with different swirler configurations
, Article Physics of Fluids ; Volume 34, Issue 8 , 2022 ; 10706631 (ISSN) ; Asadi, B ; Beige, A. A ; Sharif University of Technology
American Institute of Physics Inc
2022
Abstract
Numerical simulation of a dual-swirl gas turbine model combustor is performed under cold and reacting flow conditions using a three-dimensional unsteady Reynolds-averaged Navier-Stokes approach. A multi-species chemical mechanism is used in this study for the analysis of the numerous radicals participating in the ignition process and the flame structure. The other objective of this study is to investigate the flow field under different injector configurations, including both co-rotating and counter-rotating swirler arrangements, different swirl intensities, and vane areas. A comparison of the results with experimental data shows that the predicted velocity and temperature profiles follow the...
Analytical and numerical biaxial bending analysis of deepwater riser due to vortex-induced vibration
, Article Journal of Marine Science and Technology (Japan) ; Volume 27, Issue 1 , 2022 , Pages 492-507 ; 09484280 (ISSN) ; Komachi, Y ; Sharif University of Technology
Springer Japan
2022
Abstract
Previous studies of analysis and prediction of marine risers responses usually focus on vortex-induced vibration (VIV) of cross-flow (CF) direction rather than in-line (IL). Recent studies show that responses of IL direction tend to dominate in some cases. Responses of long riser due to biaxial bending of IL and CF VIV are investigated. Closed-form formulas are derived for estimating maximum normal stress due to the biaxial moment of CF/IL VIV and relations for estimating biaxial stress using CF values are presented. Analytical results are compared with numerical results of the time domain model and a good correlation is observed. It is shown that for tension and bending-controlled modes of...
Plasma actuator effects on the flow physics of dynamic stall for a vertical axis wind turbine
, Article Physics of Fluids ; Volume 34, Issue 7 , 2022 ; 10706631 (ISSN) ; Ebrahimi, A ; Sharif University of Technology
American Institute of Physics Inc
2022
Abstract
Darrieus type vertical axis wind turbines have several advantages over other wind turbines for local electricity generation in urban environments. However, the main aerodynamic challenge is the negative impacts of the dynamic stall phenomenon on the turbine performance. This study numerically scrutinizes the effects of plasma actuators on the dynamic stall control and performance improvement of a Darrieus turbine. For this sake, unsteady Reynolds-averaged Navier-Stokes equations are solved using a pressure-based finite volume method. The Suzen-Hoang plasma actuator model is employed to calculate the body forces attributed to the plasma actuator. First, the dynamic stall characteristics of...
Waste heat recovery of the turbocharged engine employing vortex tube for improving transient cold start
, Article Journal of Mechanical Science and Technology ; Volume 36, Issue 2 , 2022 , Pages 1015-1024 ; 1738494X (ISSN) ; Chitsaz, I ; Hanani, S. K ; Monemi, M ; Sharif University of Technology
Korean Society of Mechanical Engineers
2022
Abstract
Most of the vehicle pollutants during emission tests are raised from catalyst inefficiency during cold start. Catalysts usually convert harmful emissions only when their temperature reaches around 250 °C to 350 °C. In this research, the vortex tube is implemented to recover the waste heat energy of exhaust gas during the cold start to improve catalyst heating. The experiments are conducted on the turbocharged direct-injection gasoline engine to extract the boundary conditions of numerical simulations. Numerical simulations are performed to evaluate the effects of different hot exhaust mass fractions on the flow regime and waste heat recovery. The results reveal that the level of turbulence...
Design Optimization of Pouring basin in the Shape Casting Process
, M.Sc. Thesis Sharif University of Technology ; Davami, Parviz (Supervisor) ; Tavakoli, Rohollah (Supervisor)
Abstract
The pouring basin is a main part in the gating system. The formation of a vortical flow is a big problem occurs during the discharge of melt from the pouring basin. The vortex formation can enter the floating slag and inclusion into the mold. In the case that the vortex is more stronger, a fully air core to the sprue forms and leads to entraining of the air to the mold. These phenomena can decrease the casting quality significantly. Therefore preventing of the vortex is necessary to produce a sound cast. In this study the mechanism of vortex formation is investigated and several solutions are presented to avoid its detrimental effects. For this purpose discharge of a tank is simulated...
Numerical Simulation of Flow and Thermal Field of Film Cooling using Fan-Shaped and Antivortex Holes
, M.Sc. Thesis Sharif University of Technology ; Mazaheri, Karim (Supervisor)
Abstract
In present study physics film cooling with two rows fan shape’s holes with RSM turbulence model is simulated. At the first, structure of flow in film cooling with fan shape’s holes is identified, Then effective flow parameters and geometry parameters in film cooling problem with 2 rows fan shape’s holes is investigated. As the result of present study, four transverse arrangements for arrangement is leading to optimum effectiveness is introduced. The continuing effects of trench in cylindrical and fan-shaped holes are investigated. Finally, the efficiency of film cooling cylindrical and fan-shaped holes compared with the anti vortex holes . The results show fan-shaped holes in the high...
Numerical Investigation of Bidirectional Swirl Flow’s Structure in Vortex Engine
, M.Sc. Thesis Sharif University of Technology ; Saidi, Mohammad Hasan (Supervisor)
Abstract
Numerical investigation of flow field and determination of velocity components in swirl flow are novel and important subjects in combustion chamber of swirl flow. The exact understanding of vortex phenomena and flow structures in vortex engine results in better design and control in terms of stability, geometry, cooling, and combustion efficiency. Although, numerical approaches are computationally complex, they are worthwhile and efficient. The aim of this work is to study the velocity field in a bidirectional swirl flow within the combustion chamber using numerical approaches. The investigation of flow field has been performed in the cold chamber. Four different models (RSM and LES) have...
Effect of Air by Oxygen Enrichmenton Burning Rate of Polyethylen in Vortex Ramjet
, M.Sc. Thesis Sharif University of Technology ; Ghafoorian, Akbar (Supervisor) ; Ghorbanian, Kaveh (Supervisor) ; Saeedi, Mohammad Hassan (Co-Advisor) ; Mozaffari, Ali Asghar (Co-Advisor)
Abstract
Bidirectional axial vortex flow and air enriched with oxygen are used in order to increase solid fuel burning rate in both subsonic and supersonic ramjet engines experimentally. Vortex flow enhances combustion by causing erosive burning on the surface of the solid fuel. Air enriched by oxygen increases the combustion temperature. Therefore, they make the usage of subsonic ramjet engines possible for applications in which a low thrust is need for a long duration. An experimental ramjet engine with the capability of simulating subsonic and supersonic flight conditions was designed and fabricated. Polyethylene and oxygen enriched air are used as solid fuel and oxidizer respectively. ...
Numerical and Experimental Investigation of Swirl and Preheat Effects in a Double-Swirl Gas Turbine Model Combustor
, M.Sc. Thesis Sharif University of Technology ; Mardani, Amir (Supervisor)
Abstract
High swirl combustors with circulative structures in the flow field, have a highly flame stability with a wide range of operating conditions. In this study, Sharif Gas Turbine Model Combustor (SGTMC) which is a double high swirl burner, was investigated experimentally and numerically. In experimental studies, SGTMC with different settings of swirlers is investigated in terms of flame lean blow-out(LBO), wall temperature, the exhaust gas composition and pollutant and also flame geometry parameters. Setting of burner are changed by variations in air fraction between inner and outer air inlets or swirlers’ vanes degrees and flow rotation directions. The results indicate that the concentrations...
Numerical Simulation of A Vortex Cooled Combustion Chamber
,
M.Sc. Thesis
Sharif University of Technology
;
Farshchi, Mohammad
(Supervisor)
Abstract
The aim of the present research is to investigate the combustion chamber cooling with vortex method in presence of kerosene and liquid oxygen as propellants. For this purpose, a part of oxidizer is entered into the cylindrical combustion chamber tangentially (from bottem of the chamber), and creates a vortex flow (outer vortex). With motion of created outer vortex along the wall and eventually hit its top wall (the head of the chamber), secondary vortex (inner vortex) occurs along the center line, with a downward direction (opposite to the primary vortex). The fuel and other part of the oxidizer injection is also carried in the head of chamber, so by mixing the fuel and oxidizer that happens...
Effect of Superhydrophobic Materials Application on the Car Body to Reduce Drag
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Khodaygan, Saeed ($item.subfieldsMap.e)
Abstract
Considering the importance of environmental issues and the limitation of fuel supplies in the world, car issues have become one of the most important debates of the day. The methods used to reduce fuel consumption and emissions of greenhouse gases are primarily aimed at changing vehicle structure to reduce drag. An external body shape has been developed to reduce drag forces over the years. Due to the existence of limitations in the actual conditions of the theory, such as the beauty and convenience production, other methods should be examined. In this study, the structure of superhydrophobic properties materials with the emphasis on innovation has been considered. In order to investigate...
Experimental Separation of Gas Condensate by Vortex Tube Cascade and Validation of Simulation Results
, M.Sc. Thesis Sharif University of Technology ; Farhadi, Fathollah (Supervisor)
Abstract
The aim of this study is to survey the ability of vortex tube cascade for separating heavy components of a gas mixture. For this purpose, three vortex tubes based on previous experiences have been manufactured. Also, a helical double pipe heat exchanger has been designed and constructed. Because of the vortex tube’s ability in developing thermal separation, the effect of thermophysical parameters like feed’s temperature, inlet and outlet pressure of air on the thermal separation performance were evaluated. The recommended correlations for estimating outlet temperature of hot and cold flows, have been validated against experimental data. Moreover, various arrangements of vortex tubes to...
Vibration Analysis of Tension Leg Platform’s Tendon
, M.Sc. Thesis Sharif University of Technology ; Tabeshpour, Mohammad Reza (Supervisor) ; Mehdigholi, Hamid (Co-Advisor)
Abstract
Tension leg platforms (TLPs) are well-known structures for oil exploitation in deep water. Tethers are one of the most important component of these structures. Nonlinear response of TLP tethers under the combined action of wave and current was investigated in the present issue. Both the quadratic damping due to fluid resistance and parametric excitation due to top tension variations are included in the mathematical model. Only the vortex-induced transverse oscillations under lock on conditions were examined. A fourth order runge-kutta method was used to solve the equations of motion of tendons. The effects of surge motion coupling on the heave motion, the effects of tendon's oscillation on...
Simulation of Cooling System for ER24PC Locomotive Diesel Engine and Investigation of the Effect of Ambient Condition on the Cooling System Performance
, M.Sc. Thesis Sharif University of Technology ; Saeedi, Mohammad Hassan (Supervisor) ; Kazemzadeh Hannani, Siamak (Co-Advisor)
Abstract
Nowadays, computer simulations have an important role in the investigation of the thermal performance of the systems. In this thesis, a software program was developed for simulation of cooling system of an ER24PC Locomotive diesel engine. For this purpose, the C + + programming language is applied. One of the most important components in the cooling system is the radiator. In order to model the radiator, a relationship must be used to determine the heat transfer coefficient for coolant side and air side of the radiator. This relationship can be based on experimental, analytical, or numerical solutions. Offset strip fins are used in radiator of ER24PC locomotives. With application of...
Design and Performance Analysis of a Reversible Axial Flow Fan and Study of Symmetric Profile Effects
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Farhanieh, Bijan (Co-Advisor)
Abstract
Smoke must be exhausted, as the first action, in probable fire in subways, underground transportation systems and mines in order to survive people exposed to it. To achieving this purpose, the axial fan should be used to move the smoke to the exit lines. These fans should be had same performances in suction and discharge directions (main and reverse directions). This means flow rate should be the same at main and reverse directions. Therefore, fully reversible axial flow fans should be used in emergency ventilations. The fully reversible axial flow fans have same efficiencies in suction and discharge directions. The symmetric profiles should be used in manufacturing of the blades of these...
Simulation of Drag Reduction via Microgrooves Using Lattice Boltzmann Method
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Arghavani, Jamal (Supervisor)
Abstract
Nowadays, the lattice Boltzmann method has been widely used by scientists and engineers as an alternative to conventional numerical solvers for the Naiver-Stokes equations. The drag force decrease on the surfaces in industrial applications special in transport industries has always been of special importance. In the current research, the effects of the drag decrease has been investigated by making some rectangular grooves on the millimeter and micrometer scale on a flat surface that has been under external laminar flow of a single-phase fluid with the uniform type. Making grooves on the surfaces usually lead to change the contact area from the solid-fluid to fluid-fluid in the grooves area....
An Experimental Investigation of Unsteady Flow Over a Delta Wing in Supersonic Regime
, M.Sc. Thesis Sharif University of Technology ; Soltani, Mohammad Reza (Supervisor)
Abstract
Focusing on unsteady flow field over delta wings due to vacuity of researches in this branch on one hand and requiring of modern aircrafts designers to this science on the other hand, expresses necessity of accomplishing present investigation. Scrutiny of pressure distribution of low aspect ratio wings in unsteady state and determination of aerodynamic characteristics of these wings in variant conditions, can be beneficial to plan aircrafts need to fly with high maneuverability in high speeds. This issue becomes important when in supersonic regime, with respect to emerged shock waves and vortices, develop complicated pressure distributions on the wing surface in unsteady state that affect...
Theoretical and Experimental Modeling of Vortex Engine in Ramjet Application
, M.Sc. Thesis Sharif University of Technology ; Ghafourian, Akbar (Supervisor) ; Saeedi, Mohsen (Supervisor) ; Mozaffari, Ali Asghar (Supervisor)
Abstract
Heat transfer to combustion chamber walls is an unwanted phenomenon. Reduction of this heat transfer by using bidirectional swirl flow, as proved in past studies, can result in time and cost saving methods in design and fabrication of combustion chambers. Bidirectional Swirl flow, existing in vortex engine, maintains the chamber wall cool. This characteristic of such flow field, among with many other advantages for it, makes researchers more interested in studying the propulsion of it as well as its other applications. Bidirectional swirl flow in liquid fuel ramjet engines has the proven advantage of keeping the combustion chamber walls cool and in solid fuel ramjet engines in increasing the...