Search for: turbulence
Total 420 records
Effects of pulsation on grid-generated turbulence, Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 123, Issue 4 , 2001 , Pages 948-958 ; 00982202 (ISSN) ; Jerphanion, I ; Magaud, F ; Souhar, M ; Sharif University of Technology
The effects of low frequency, large amplitude sinusoidal pulsation on grid-generated turbulence (PGGT) were experimentally studied. Two-component hot wire anemometry technique was used. Pulsation did not change homogeneous, isotropic character of grid-generated turbulence. © 2001 by ASME
New turbulence modeling for air/water stratified flow, Article Journal of Ocean Engineering and Science ; Volume 5, Issue 1 , 2020 , Pages 55-67 ; Ghofrani, M. B ; Sharif University of Technology
Shanghai Jiaotong University 2020
The prediction of interfacial turbulence characteristics is one of the still challenging of two-phase stratified flow. The evaluation of some important parameters such as interfacial heat transfer coefficient based on turbulence kinetic energy and turbulence dissipation rate in some models, intensifies the importance of turbulence flow correct simulation. High gradient of velocity and turbulence kinetic energy at the interface of two-phase stratified flow leads to a major overestimation or underestimation of flow characteristics without any special treatment. Consideration of a source function of turbulence eddy frequency at the interface is one of the common solution employed in past...
Markov properties of electrical discharge current fluctuations in plasma, Article Journal of Statistical Physics ; Volume 143, Issue 1 , 2011 , Pages 148-167 ; 00224715 (ISSN) ; Movahed, M. S ; Khorram, S ; Rahimi Tabar, M. R ; Sharif University of Technology
Using the Markovian method, we study the stochastic nature of electrical discharge current fluctuations in the Helium plasma. Sinusoidal trends are extracted from the data set by the Fourier-Detrended Fluctuation analysis and consequently cleaned data is retrieved. We determine the Markov time scale of the detrended data set by using likelihood analysis. We also estimate the Kramers-Moyal's coefficients of the discharge current fluctuations and derive the corresponding Fokker-Planck equation. In addition, the obtained Langevin equation enables us to reconstruct discharge time series with similar statistical properties compared with the observed in the experiment. We also provide an exact...
Experiments on pulsation effects in turbulent flows, Part I: Investigation on Simple Shear Flows, Article Scientia Iranica ; Volume 10, Issue 2 , 2003 , Pages 238-247 ; 10263098 (ISSN) ; Hajilouy, A ; Farshchi, M ; Souhar, M ; Sharif University of Technology
Sharif University of Technology 2003
This article describes the results of experimental observations in pulsating Simple Shear Flows (SSF). A uniform-mean-gradient shear flow was generated within the test section of an open circuit wind tunnel. Transverse arrays of honeycomb channels with differing resistances were used to generate shear flow at low shear rates (less than 20 s-1). A set of rotating vanes pulsated the flow field at 8.5 Hz and 18 Hz. Instantaneous velocity was measured by employing a two-component hot wire anemometry technique. The experimental credibility of the facility was established in stationary SSF. In pulsating flows the pulsation effects on mean shear rate, the kinetic energy of turbulence, Reynolds...
Experiments on pulsation effects in turbulent flows, Part II: Investigation on grid-generated turbulence, Article Scientia Iranica ; Volume 10, Issue 2 , 2003 , Pages 248-251 ; 10263098 (ISSN) ; Hajilouy, A ; Farshchi, M ; Souhar, M ; Sharif University of Technology
Sharif University of Technology 2003
In this paper, pulsating grid-generated turbulence is studied. A two-component hot wire anemometry technique is used. The pulsation effects on characterizing lenght scales and the statistical description of fluctuations are studied in comparison with their stationary counterparts. No significant change in the character of the turbulent flow with pulsation is observed
Experimental investigation of turbulence specifications of 3-D density currents, Article 2007 5th Joint ASME/JSME Fluids Engineering Summer Conference, FEDSM 2007, San Diego, CA, 30 July 2007 through 2 August 2007 ; Volume 1 SYMPOSIA, Issue PART A , August , 2007 , Pages 789-796 ; 0791842886 (ISBN); 9780791842881 (ISBN) ; Afshin, H ; Baghaer Poor, A ; Sharif University of Technology
The present study investigates the turbulence characteristic of density current experimentally. The 3D Acoustic-Doppler Velocimeter (ADV) was used to measure the instantaneous velocity and characteristics of the turbulent flow. The courses of experiment were conducted in a three-dimensional channel for different discharge flows, concentrations, and bed slopes. Results are expressed at various distances from the inlet, for all flow rates, slopes and concentrations as the distribution of turbulence energy, Reynolds stress and the turbulent intensity. It was concluded that the maximum turbulence intensity happens in both the interface and near the wall. Also it was observed that turbulence...
Computation of turbulent flow over highly curved configuration using a conventional two-equation turbulence model, Article 45th AIAA Aerospace Sciences Meeting 2007, Reno, NV, 8 January 2007 through 11 January 2007 ; Volume 9 , 2007 , Pages 6262-6275 ; 1563478900 (ISBN); 9781563478901 (ISBN) ; Taeibi Rahni, M ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc 2007
A new procedure for simulating turbulent flow in three-dimensional arbitrary geometries is presented. Finite volume method using physical covariant velocities on a staggered grid arrangement was used in this investigation. This work is an extension of previous successful work to three-dimensional cases. The ability of the new algorithm was tested using a conventional two-equation turbulence model on a highly separated turbulent flow test case. The low Reynolds number k-ω turbulence model of Wilcox was utilized to evaluate its capability in modeling highly curved flows. Turbulent flow over a three-dimensional hill, which is appropriate in assessment of ability of turbulence models in...
Multiscale probability distribution of pressure fluctuations in fluidized beds, Article Journal of Statistical Mechanics: Theory and Experiment ; Volume 2012, Issue 7 , 2012 ; 17425468 (ISSN) ; Sahimi, M ; Rahimi Tabar, M. R ; Peinke, J ; Sharif University of Technology
Analysis of flow in fluidized beds, a common chemical reactor, is of much current interest due to its fundamental as well as industrial importance. Experimental data for the successive increments of the pressure fluctuations time series in a fluidized bed are analyzed by computing a multiscale probability density function (PDF) of the increments. The results demonstrate the evolution of the shape of the PDF from the short to long time scales. The deformation of the PDF across time scales may be modeled by the log-normal cascade model. The results are also in contrast to the previously proposed PDFs for the pressure fluctuations that include a Gaussian distribution and a PDF with a power-law...
Fully developed turbulence in the view of horizontal visibility graphs, Article Journal of Statistical Mechanics: Theory and Experiment ; Volume 2015, Issue 8 , Agu , 2015 ; 17425468 (ISSN) ; Rahimi Tabar, M. R ; Peinke, J ; Sharif University of Technology
Institute of Physics Publishing 2015
We employ the horizontal visibility algorithm to map the velocity and acceleration time series in turbulent flows with different Reynolds numbers, onto complex networks. The universal nature of velocity fluctuations in high Reynolds turbulent Helium flow is found to be inherited in the corresponding network topology. The degree distributions of the acceleration series are shown to have stretched exponential forms with the Reynolds number dependent fitting parameter. Furthermore, for acceleration time series, we find a transitional behavior in terms of the Reynolds number in all network features which is in agreement with recent empirical studies
Experimental investigation of turbulence specifications of turbidity currents, Article Journal of Applied Fluid Mechanics ; Volume 3, Issue 1 , 2010 , Pages 63-73 ; 17353572 (ISSN) ; Afshin, H ; Bagherpour, A ; Sharif University of Technology
The present study investigates the turbulence characteristic of turbidity current experimentally. The three-dimensional Acoustic-Doppler Velocimeter (ADV) was used to measure the instantaneous velocity and characteristics of the turbulent flow. The experiments were conducted in a three-dimensional channel for different discharge flows, concentrations, and bed slopes. Results are expressed at various distances from the inlet, for all flow rates, slopes and concentrations as the distribution of turbulence energy, Reynolds stress and the turbulent intensity. It was concluded that the maximum turbulence intensity happens in both the interface and near the wall. Also, it was observed that the...
3-D simulation of turbulent density, 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) ; Firoozabadi, B ; Afshin, H ; Ghasvari Jahromi, H ; Sharif University of Technology
Density current is a dense fluid, which is continuously released from a source and spreads down a sloping surface inside a lighter, motionless fluid. A low-Reynolds number k-ε model (Launder and Sharma, 1974) has been used to simulate the behavior of 3-D density currents. Density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. The model has been verified with the experimental data sets. Although the k-ε Launder and Sharma model is applied here to a conservative density current, it seems the analysis is valid in general for turbidity current laden with fine particles. Copyright © 2006 by ASME
Finite element volume analysis of propane preheated air flame passing through a minichannel, Article ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels, ICNMM 2014, Collocated with the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting ; 2014 ; Ghafourizadeh, M ; Schneider, G. E ; Sharif University of Technology
A hybrid finite-element-volume FEV method is extended to simulate turbulent non-premixed propane air preheated flame in a minichannel. We use a detailed kinetics scheme, i.e. GRI mechanism 3.0, and the flamelet model to perform the combustion modeling. The turbulence-chemistry interaction is taken into account in this flamelet modeling using presumed shape probability density functions PDFs. Considering an upwind-biased physics for the current reacting flow, we implement the physical influence upwinding scheme PIS to estimate the cell-face mixture fraction variance in this study. To close the turbulence closure, we employ the two-equation standard κ-ε turbulence model incorporated with...
Power spectrum and FFT-based signal analysis in turbulence measurements, Article World Academy of Science, Engineering and Technology ; Volume 40 , 2009 , Pages 275-278 ; 2010376X (ISSN) ; Tamadonfar, P ; Soltani, M. R ; Ghorbanian, K ; Masdari, M ; Sharif University of Technology
In this research, the employment of an innovative but simple and cost effective method for turbulent reduction in a low speed wind tunnel is investigated and the effect of this turbulence reduction on the Power Spectrum and FFT-Based signals that obtained from Hot-wire Anemometry is studied. These terms represents the amount of power contained in the signals. Several situations are studied in this paper. One of these situations is when there are four screens in the settling chamber of the wind tunnel and after that by adding the trip strip in the contraction region of the wind tunnel the tests were repeated. In the next stage, three screens were removed from the settling chamber of the wind...
On the effect of inflow conditions in simulation of a turbulent round jet, Article Archive of Applied Mechanics ; Volume 81, Issue 10 , 2011 , Pages 1439-1453 ; 09391533 (ISSN) ; Saemi, S. D ; Maddahian, R ; Farhanieh, B ; Sharif University of Technology
This paper investigates the impact of the inflow conditions on simulations of a round jet discharging from a wall into a large space. The fluid dynamic characteristics of a round jet are studied numerically. A numerical method based on the control volume approach with collocated grid arrangement is employed. The k-ε model is utilized to approximate turbulent stresses by considering six different inlet conditions. The velocity field is presented, and the rate of decay at the jet centerline is determined. The results showed that inflow conditions had a strong influence on the jet characteristics. This paper also investigates both sharp-edged and contoured nozzles. The effects of velocity,...
Numerical simulation of turbid-density current using v2̄ - f turbulence model, Article 2005 ASME International Mechanical Engineering Congress and Exposition, IMECE 2005, Orlando, FL, 5 November 2005 through 11 November 2005 ; Volume 261 FED , 2005 , Pages 619-627 ; 08888116 (ISSN); 0791842193 (ISBN); 9780791842195 (ISBN) ; Firoozabadi, B ; Farhanieh, B ; Sharif University of Technology
The deposition behavior of fine sediment is an important phenomenon, and yet unclear to engineers concerned about reservoir sedimentation. An elliptic relaxation turbulence model (v2̄ - f model) has been used to simulate the motion of turbid density currents laden whit fine solid particles. During the last few years, the v2̄ - f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proved that the v2̄ - f model to be superior to other RANS methods in many fluid flows where complex flow features are present. Due to low Reynolds number turbulence of turbidity current,(its critical Reynolds...
Oil-soluble drag-reducing polymers [electronic resource], Article Journal of polymer materials ; December 1994, Volume 11, Number 4; Page(s) 239 To 247 ; Pourjavadi, A ; Nadali, M ; Sharif University of Technology
This article reviews the oil-soluble polymeric drag-reducing agents (DRAs) with an outlook to their large-scale application in petroleum industry. A general discussion on mechanism of the DR phenomenon and mechanical degradation of the drag reducers in turbulent flow is offered with an emphasis on the molecular parameters. Furthermore, low charge density associating polymers, as a new class of oil-soluble flow improvers, are described
Computational Simulation of Flow over a Cylinder in Ground Effect, Using PANS, Article Life Science Journal ; Volume 10, Issue SUPPL 8 , 2013 , Pages 195-202 ; 10978135 (ISSN) ; Salimi, M ; Taeibi Rahni, M ; Mahdavimanesh, M ; Sharif University of Technology
Recently, very large eddy simulation approach has attracted a great deal of attention among researchers. This approach can be thought of as an intermediate approach in flow field filtering view point compared with Direct Numerical Simulation and Reynolds-Averaged Navier-Stokes. One famous method to this approach is Partially Averaged Navier-Stokes. Early studies have demonstrated the capability of this technique in flow prediction; however, this method still needs to be evaluated under more flow conditions to ensure its reliable performance. In this study, the performance of PANS k-ω method in the simulation of turbulent flow around a cylinder with square cross section close to a flat...
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
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,...
Control of separation in the concave portion of contraction to improve the flow quality, Article Aeronautical Journal ; Volume 113, Issue 1141 , 2009 , Pages 177-182 ; 00019240 (ISSN) ; Soltani, M.R ; Manshadi, M.D ; Mirzaei, M ; Sharif University of Technology
Subsonic wind tunnel experiments were conducted to study the effect of forced transition on the pressure distribution in the concave portion of contraction. Further more, the effect of early transition on the turbulence level in the test section of the wind tunnel is studied. Measurements were performed by installing several trip strips at two different positions in the concave portion of the contraction. The results show that installation of the trip strips, have significant effects on both turbulence intensity and on the pressure distribution. The reduction in the free stream turbulence as well as the wall static pressure distribution varied significantly with the location of the trip...
Fractal analysis of discharge current fluctuations, Article Journal of Statistical Mechanics: Theory and Experiment ; Volume 2009, Issue 3 , 2009 ; 17425468 (ISSN) ; Sadegh Movahed, M ; Khorram, S ; Sobhanian, S ; Rahimi Tabar, M. R ; Sharif University of Technology
Institute of Physics Publishing 2009
We use multifractal detrended fluctuation analysis (MF-DFA) to study the electrical discharge current fluctuations in plasma and show that it has multifractal properties and behaves as a weak anti-correlated process. Comparison of the MF-DFA results for the original series with those for the shuffled and surrogate series shows that correlation of the fluctuations is responsible for the multifractal nature of the electrical discharge current. © 2009 IOP Publishing Ltd. and SISSA