Sharif Digital Repository

The present study provides a comparison between the flow pattern around two circular piers in tandem and a single pier set up on a moderately rough flat bed in a laboratory flume. Velocities are measured by an Acoustic Doppler Velocimeter (ADV). The contours of the time-averaged velocity components, Reynolds shear stresses, turbulence intensities and turbulence kinetic energy at different planes are presented. Streamlines and vectors are used to study the flow features. The analysis of power spectra around the piers is also presented. The results show that the presence of downstream pier changes the flow structure to a great extent, particularly in the near-wake region. Within the gap... 

The present study provides the experimental results of the flow pattern around two-circular piers positioned in side-by-side arrangement. The experiments were performed for two bed configurations (with and without a scour hole). Velocities were measured by an Acoustic Doppler Velocimeter (ADV). Flat bed and scour hole were frozen by synthetic glue to facilitate the performance of the experiments. The contours and distributions of the time-averaged velocity components, turbulence intensities, turbulence kinetic energy, and Reynolds stresses at different horizontal and vertical planes are presented. Streamlines and velocity vectors obtained from time-averaged velocity fields are used to show... 

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... 

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,... 

Experiments are performed to evaluate the impact of trip wires on the turbulence intensity in a few low speed wind tunnels. Trip wires of different sizes are installed at different positions in the contraction section of four different wind tunnels and measurements are made at various free stream velocities. The results indicate that the pressure distributions are altered compared to the clean condition. Trip wires move the adverse pressure gradient toward the inlet of the contraction section. Consequently, the turbulence intensity in the test section of the wind tunnels is reduced and the flow uniformity is improved considerably. Frequency and statistical analysis are performed and the... 

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... 

In this paper, three-dimensional turbulent flow field around a complex bridge pier placed on a rough fixed bed is experimentally investigated. The complex pier foundation consists of a column, a pile cap, and a 2×4 pile group. All of the elements are exposed to the approaching flow. An acoustic-Doppler velocimeter was used to measure instantaneously the three components of the velocities at different horizontal and vertical planes. Profiles and contours of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses, as well as velocity vectors are presented and discussed at different vertical and horizontal planes. The approaching... 

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,... 

In this work, we numerically study the effects of turbulence intensity at the fuel and oxidizer stream inlets on the soot aerosol nano-particles formation in a kerosene fuel-based combustor. In this regard, we study the turbulence intensity effects specifically on the thermal performance and nanoparticulate soot aerosol emissions. To construct our computer model, we simulate the soot formation and oxidation using the Polycyclic Aromatic Hydrocarbons PAHs-inception and the hydroxyl concept, respectively. Additionally, the soot nucleation process is described using the phenyl route, in which the soot inception is described based on the formations of tworinged and three-ringed aromatics from... 

In case of unexpected ruptures in high pressure tanks, choking phenomenon occurs in the cracked area which fluid velocity gets sonic and its pressure exceeds atmospheric pressure. Afterward, pressure of discharged gas quickly changes by crossing through compression and expansion shock waves. The main aim of this study was numerical simulation and investigation of this flow in a 3-step process: (a) Detailed analysis of numerical method, (b) Qualitative and quantitative analysis of velocity, pressure, temperature and turbulence intensity, in order to propose safety strategies and (c) parametric studies on the effects of tank pressure and nozzle geometry on flow structure. In numerical... 

Subsonic wind tunnel experiments were conducted to study the effect of tripped boundary layer on the pressure distribution in the contraction region of the tunnel. Measurements were performed by installing trip strip 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 and pressure distribution. The reduction in the free stream turbulence and reduction of the wall static pressure distribution deferred signified with the location of the trip strip  

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... 

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... 

A numerical study has been performed to investigate the flow and heat transfer characteristics of fluid flow through heat exchanger tubes fitted with perforated conical rings. The holes are circular, and the number of holes N is ranged from 0 to 10. The influences of perforated conical ring diameter ratios D2/D1=0.4,0.5and0.6 and the hole diameter ratios d/D=0.06,0.1and0.14 on average Nusselt number, friction factor and thermal performance factor are reported. This analysis is performed in the turbulent flow regime 4000⩽Re⩽14,000 and the governing equations are solved by using (RNG) k-∊ model. Due to strong turbulent intensity, perforated conical rings lead to more flow perturbation and... 

In this study, factors affecting the noise generation by instability waves in a subsonic jet with acoustic Mach number of 0.5 are investigated using linear stability analysis. The base flow required for instability analysis is obtained by modeling the jet stream based on the k-ϵ turbulence model and using the empirical coefficients suggested by Thies and Tam [1]. The resulting base flow profiles are used to solve the linear instability equation, which governs the pressure perturbation for obtaining the eigenvalues and eigenfunctions. The results of linear instability analysis for phase and amplitude of pressure fluctuations are compared against the existing experimental data, which... 

In this study, factors affecting the noise generation by instability waves in a subsonic jet with acoustic Mach number of 0.5 are investigated using linear stability analysis. The base flow required for instability analysis is obtained by modeling the jet stream based on the k-ϵ turbulence model and using the empirical coefficients suggested by Thies and Tam [1]. The resulting base flow profiles are used to solve the linear instability equation, which governs the pressure perturbation for obtaining the eigenvalues and eigenfunctions. The results of linear instability analysis for phase and amplitude of pressure fluctuations are compared against the existing experimental data, which... 

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... 

Large-eddy simulations are carried out for a particle-laden vertical turbulent channel flow at Reynolds number of 180 based on friction velocity and channel half-width. To minimize the numerical and aliasing errors, a fourth-order compact finite-volume method in space and a fourth-order Runge-Kutta method in time along with a dynamic Smagorinsky model with explicit filter-grid size ratio 2 have been used to solve the filtered equations of the carrier flow. Heavy, small particle motion is governed by drag, gravitational, and Saffman lift forces in the Lagrangian frame. These particle equations are integrated in time using a second-order Adams-Bashforth method. The effect of subgrid-scale...