Loading...
Search for:
subsonic-flow
0.009 seconds
DSMC simulation of subsonic flow through nanochannels and micro/nano backward-facing steps
, Article International Communications in Heat and Mass Transfer ; Volume 38, Issue 10 , 2011 , Pages 1443-1448 ; 07351933 (ISSN) ; Roohi, E ; Sharif University of Technology
2011
Abstract
In this study, we use direct simulation Monte Carlo method to simulate subsonic flow in nanochannels and micro/nanoscale backward-facing (BF) step considering a wide range of Knudsen number regimes. The nanochannel flow simulation indicates that the nanoscale flow through the nanochannel resembles unique features such as encountering negative pressure deviation behavior and observing flat velocity profiles at higher Knudsen number regimes. On the other hand, the micro/nano BF step flow simulations demonstrate that the length of separation region considerably decreases as the flow becomes more rarefied and approaches the transition regime. Meanwhile, the variations in the flow properties are...
Comparison of the unsteady loads of an airfoil in the pitching and plunging motions
, Article 2006 ASME Joint U.S.- European Fluids Engineering Division Summer Meeting, FEDSM2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2 FORUMS , 2006 , Pages 977-985 ; 0791847500 (ISBN); 9780791847503 (ISBN) ; Seddighi, M ; Rasi, F ; Sharif University of Technology
American Society of Mechanical Engineers
2006
Abstract
A series of experiments were conducted on an oscillating airfoil in subsonic flow. The model was oscillated in two types of motions, pitch and plunge, at different velocities, and reduced frequencies. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The imposed variables of the experiment were reduced frequency, mean incident angle, amplitude of motion, and free stream velocity as well as the surface grit roughness. The unsteady aerodynamic loads were calculated using surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different type of...
Comparison of the unsteady loads of an airfoil in the pitching and plunging motions
, Article 2006 2nd ASME Joint U.S.-European Fluids Engineering Summer Meeting, FEDSM 2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2006 , 2006 ; 0791837831 (ISBN); 9780791837832 (ISBN) ; Seddighi, M ; Rasi, F ; Sharif University of Technology
2006
Abstract
A series of experiments were conducted on an oscillating airfoil in subsonic flow. The model was oscillated in two types of motions, pitch and plunge, at different velocities, and reduced frequencies. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The imposed variables of the experiment were reduced frequency, mean incident angle, amplitude of motion, and free stream velocity as well as the surface grit roughness. The unsteady aerodynamic loads were calculated using surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different type of...
Experimental investigation of Pressure Distribution over Delta Wing in
Sub/supersonic Speed
,
M.Sc. Thesis
Sharif University of Technology
;
Soltani, Mohammad Reza
(Supervisor)
Abstract
Flow characteristics analysis over a wing, is one of the pioneer challenges in super and sub-sonic flow near flying objects. Taking into account of growing rate of low aspect ratio utilization, usually called Delta wings, investigation of vortex behavior over this wings is highly noticeable. In addition, the lack of research in this branch of Aerodynamics inside the country, considering it’s critical application, has doubled the importance of doing research in this filled. Experimental researches on super-sonic flow over a Delta wing is limited and there are not much accurate researches about vortexes in this category of wings. In this work, the main effort is to investigate the phenomena in...
Investigation of Energy Harvesting from a Fluttering Plate in Subsonic Flow via Piezoelectric Materials
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firoozabadi, Rouhollah (Supervisor)
Abstract
One can use the vibrational energy available in environment to harvest energy via piezoelectric materials, for various applications and this research field has received growing attention by researchers over the last years. This research motivation is, harvesting electrical energy from a fluttering plate in 2D axial flow via piezoelectric materials. For this purpose, a nonlinear Euler-Bernoulli beam model is used to model structure, an incompressible 2D vortex lattice method is used to model the aerodynamics, and coupled linear piezoelectric electro-mechanical equations is used to model piezoelectric materials. The structure is considered into axial flow, and flow speed gradually increases,...
Recommendations on performance of parallel DSMC algorithm in solving subsonic nanoflows
, Article Applied Mathematical Modelling ; Volume 36, Issue 5 , May , 2012 , Pages 2314-2321 ; 0307904X (ISSN) ; Darbandi, M ; Sharif University of Technology
2012
Abstract
We investigate the efficiency of a parallel direct simulation Monte Carlo (PDSMC) algorithm in solving the rarefied subsonic flow through a nanochannel. We use MPI library to transfer data between the processors. It is observed that PDSMC solver shows ideal speed up if sufficient workload is provided for each of processors. Additionally, this study shows that the computational time and speed up of the extended PDSMC solver do not depend (or slightly depend) on the number of cells. In contrary, increasing the total number of particles would result in a better efficiency of the PDSMC
A new approach to investigate unsteady aerodynamic phenomena
, Article Scientia Iranica ; Volume 12, Issue 4 , 2005 , Pages 379-391 ; 10263098 (ISSN) ; Davari, A. R ; Sharif University of Technology
Sharif University of Technology
2005
Abstract
A new approach, based on a Generalized Regression Neural Network (GRNN), has been proposed to predict the unsteady forces and moments of two different models; a 70° swept delta wing in subsonic incompressible flow and a standard fighter model (SDM) in a compressible flow regime, both undergoing sinusoidal pitching motion. Extensive wind tunnel results were used for training the network and verification of the values predicted by this approach. GRNN was trained by the aforementioned experimental data and, subsequently, was used as a prediction tool to determine the unsteady longitudinal forces and moment of the two models under various conditions. Further, it was applied to extend the...
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...
Experimental study on correlation between turbulence and sound in a subsonic wind tunnel
, Article Acta Mechanica Sinica/Lixue Xuebao ; Volume 26, Issue 4 , 2010 , Pages 531-539 ; 05677718 (ISSN) ; Ghorbanian, K ; Soltani, M. R ; Sharif University of Technology
Abstract
In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon, and the results indicate that the trip strip has significant effects on sound reduction. The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction. Furthermore, the effect of monopole, dipole and quad- rupole sources of aerodynamic noise...
Application of screens and trips in enhancement of flow characteristics in subsonic wind tunnels
, Article Scientia Iranica ; Volume 17, Issue 1 B , 2010 , Pages 1-12 ; 10263098 (ISSN) ; Ghorbanian, K ; Manshadi, M. D ; Sharif University of Technology
2010
Abstract
Subsonic wind tunnel experiments were conducted to study the turbulence level in the test section. Measurements were performed by introducing trip strip and/or damping screens on the flow field. The results indicated that the introduction of trip strips not only reduced the turbulence intensity compared to cases without it, but also flattened the variations. Further, the experiments which investigated the impact of the damping screens indicated a similar reduction in turbulence intensity; the pattern, however, remained the same. Furthermore, the results for cases wherein both trip strips as well as damping screens were placed on the contraction and in the settling chamber, respectively,...
A high-order accurate unstructured spectral difference lattice Boltzmann method for computing inviscid and viscous compressible flows
, Article Aerospace Science and Technology ; Volume 98 , 2020 ; Ghaffarian, A ; Sharif University of Technology
Elsevier Masson SAS
2020
Abstract
In the present work, the spectral difference lattice Boltzmann method (SDLBM) is implemented on unstructured meshes for the solution methodology to be capable of accurately simulating the compressible flows over complex geometries. Both the inviscid and viscous compressible flows are computed by applying the unstructured SDLBM. The compressible form of the discrete Boltzmann–BGK equation with the Watari model is considered and the solution of the resulting system of equations is obtained by applying the spectral difference method on arbitrary quadrilateral meshes. The accuracy and robustness of the unstructured SDLBM for simulating the compressible flows are demonstrated by simulating four...
DSMC solution of supersonic scale to choked subsonic flow in micro to nano channels
, Article 6th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM2008, Darmstadt, 23 June 2008 through 25 June 2008 ; Issue PART A , 2008 , Pages 985-993 ; 0791848345 (ISBN); 9780791848340 (ISBN) ; Darbandi, M ; Mirjalili, V ; ASME ; Sharif University of Technology
2008
Abstract
In this study, the supersonic and choked subsonic flows through micro/nano channels are investigated using direct simulation Monte Carlo (DSMC) method. The supersonic case is simulated at different Knudsen numbers covering slip to transition flow regimes, while the effects of inlet Mach and back pressure are studied in details. The inlet/outlet pressure boundary conditions are suitably implemented benefiting from the basics of characteristics theory. A behavior similar to the one predicted by the Fanno theory is observed here; i.e., the supersonic flow velocity decelerates up to a choking condition where any further increase in Knudsen number is impossible unless strong normal/oblique shocks...
Design and Optimization of a Subsonic Wind Tunnel Profile with Two Test Sections using CFD
, M.Sc. Thesis Sharif University of Technology ; Darbandi, Masoud (Supervisor)
Abstract
In this project, we are willing to analyze and design a subsonic wind tunnel WT configuration for the Aerospace Engineering Department in Sharif University of Technology. This WT will be an open-circuit "suck down" type, whose entry is open to the atmosphere (laboratory) and three axial fans downstream of its test section. In addition to three parallel fans, we are expected to design two simultaneous small and large size test sections for it. The small and large sections would have an area about 1.4 and 4 m2and maintain a maximum air velocity of 100 and 50 m/s, respectively. So, our design is faced with two main complexities. In one hand, we are to manage the air flow through these two test...
Aeroelastic stability and response of composite swept wings in subsonic flow using indicial aerodynamics
, Article Journal of Vibration and Acoustics, Transactions of the ASME ; Volume 135, Issue 5 , 2013 ; 10489002 (ISSN) ; Farsadi, T ; Haddadpour, H ; Sharif University of Technology
2013
Abstract
In this study, the aeroelastic stability and response of an aircraft swept composite wing in subsonic compressible flow are investigated. The composite wing was modeled as an anisotropic thin-walled composite beam with the circumferentially asymmetric stiffness structural configuration to establish proper coupling between bending and torsion. Also, the structural model consists of a number of nonclassical effects, such as transverse shear, material anisotropy, warping inhibition, nonuniform torsional model, and rotary inertia. The finite state form of the unsteady aerodynamic loads have been modeled based on the indicial aerodynamic theory and strip theory in the subsonic compressible flow....
Effects of wing geometry on wing-body-tail interference in subsonic flow
, Article Scientia Iranica ; Volume 18, Issue 3 B , 2011 , Pages 407-415 ; 10263098 (ISSN) ; Soltani, M. R ; Askari, F ; Pajuhande, H. R ; Sharif University of Technology
Abstract
Extensive wind tunnel tests were performed on several wing- body-tail combinations in subsonic flow to study the effects of wing geometric parameters on the flow field over the tail. For each configuration, tail surface pressure distribution, as well as the velocity contour at a plane perpendicular to the flow direction behind the wing was measured. The results show a strong effect of wing to tail span ratio, as well as wing aspect ratio, on the flowfield downstream of the wing. For low sweep wings, as those considered here, wing and body interference effects on the tail are associated with the wing tip vortex and nose-body vortex
Study of gas flow in micronozzles using an unstructured dsmc method
, Article Proceedings of the 7th International Conference on Nanochannels, Microchannels, and Minichannels 2009, ICNMM2009, 22 June 2009 through 24 June 2009, Pohang ; Issue PART A , 2009 , Pages 417-424 ; 9780791843499 (ISBN) ; Darbandi, M ; Mirjalili, V ; ASME ; Sharif University of Technology
Abstract
The current research uses an unstructured direct simulation Monte Carlo (DSMC) method to numerically investigate supersonic and subsonic flow behavior in micro convergent-divergent nozzle over a wide range of rarefied regimes. The current unstructured DSMC solver has been suitably modified via using uniform distribution of particles, employing proper subcell geometry, and benefiting from an advanced molecular tracking algorithm. Using this solver, we study the effects of back pressure, gas/surface interactions (diffuse/specular reflections), and Knudsen number, on the flow field in micronozzles. We show that high viscous force manifesting in boundary layers prevents supersonic flow formation...
Aeroelastic instability analysis of a turbomachinery cascade with magnetorheological elastomer based adaptive blades
, Article Thin-Walled Structures ; Volume 130 , 2018 , Pages 71-84 ; 02638231 (ISSN) ; Navazi, H. M ; Haddadpour, H ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
Torsional aeroelastic analysis of a turbomachinery cascade comprised of three-layered sandwich blades embedded with Magnetorheological Elastomer (MRE) core layer is carried out in this paper. The MRE material is used as a constrained damping layer between two elastic skins in order to investigate its effects on the aeroelastic stability of a blade cascade. To formulate the structural dynamic of the blades, torsional theory of rectangular laminated plates is used and the unsteady Whitehead's aerodynamic theory is employed to model the aerodynamic loadings. Assumed modes method and the Lagrange's equations are used to derive the governing equations of motion of the coupled aeroelastic system....
Direct simulation Monte Carlo solution of subsonic flow through micro/nanoscale channels
, Article Journal of Heat Transfer ; Volume 131, Issue 9 , 2009 , Pages 1-8 ; 00221481 (ISSN) ; Darbandi, M ; Mirjalili, V ; Sharif University of Technology
2009
Abstract
We use a direct simulation Monte Carlo (DSMC) method to simulate gas heating/cooling and choked subsonic flows in micro/nanoscale channels subject to either constant wall temperature or constant/variable heat flux boundary conditions. We show the effects of applying various boundary conditions on the mass flow rate and the flow parameters. We also show that it is necessary to add a buffer zone at the end of the channel if we wish to simulate more realistic conditions at the channel outlet. We also discuss why applying equilibrium-based Maxwellian distribution on molecules coming from the channel outlet, where the flow is nonequilibrium, will not disturb the DSMC solution. The current...