scholarly journals Analytical Velocity Study in a Conical Diffuser with Screw Tape Inserts

2018 ◽  
Vol 153 ◽  
pp. 06003
Author(s):  
Ehan Sabah Shukri
Keyword(s):  
Reynolds Number ◽  
Numerical Analysis ◽  
Boundary Conditions ◽  
Velocity Distribution ◽  
Numerical Simulations ◽  
Swirling Flow ◽  
Working Fluid ◽  
Aspect Ratios ◽  
Conical Diffuser ◽  
Better Than

A study is made to enhance the rate of velocity distribution in a conical diffuser. In this work, a numerical analysis on screw tape inserts in a conical diffuser is presented. In the numerical simulations, the swirling flow was introduced by using rectangular screw tape placed inside the inner test wall of the conical diffuser. Screw tape with different aspect ratios (AS) 2.5, 3.5, 4.5, 6.5 and 7.5 was analysed. The simulations were carried out with constant inlet condition considering the flow turbulent and incompressible with inlet Reynolds number 3.2 × 105. The simulations were performed using air as a working fluid. The results obtained from the conical diffuser with screw tape inserts are compared with those without screw tape (plain conical diffuser). On the basis of the same inlet boundary conditions for the screw tape in the conical diffuser and the plain conical diffuser, it was found that the velocity distribution performance of screw tape inserts with different AS is better than plain conical diffuser. It is also observed that the screw tape with AS 3.5 offered the best velocity distribution rate.

scholarly journals Flow Characteristics of the Entrance Region with Roughness Effect within Rectangular Microchannels

Micromachines ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 30
Author(s):  
Haiwang Li ◽  
Yujia Li ◽  
Binghuan Huang ◽  
Tiantong Xu
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Stokes Equations ◽  
Critical Role ◽  
Flow Characteristics ◽  
Entrance Region ◽  
Working Fluid ◽  
Asymmetric Distribution ◽  
Rectangular Microchannels ◽  
Aspect Ratios

We conducted systematic numerical investigations of the flow characteristics within the entrance region of rectangular microchannels. The effects of the geometrical aspect ratio and roughness on entrance lengths were analyzed. The incompressible laminar Navier–Stokes equations were solved using finite volume method (FVM). In the simulation, hydraulic diameters ( D h ) ranging from 50 to 200 µm were studied, and aspect ratios of 1, 1.25, 1.5, 1.75, and 2 were considered as well. The working fluid was set as water, and the Reynolds number ranged from 0.5 to 100. The results showed a good agreement with the conducted experiment. Correlations are proposed to predict the entrance lengths of microchannels with respect to different aspect ratios. Compared with other correlations, these new correlations are more reliable because a more practical inlet condition was considered in our investigations. Instead of considering the influence of the width and height of the microchannels, in our investigation we proved that the critical role is played by the aspect ratio, representing the combination of the aforementioned parameters. Furthermore, the existence of rough elements obviously shortens the entrance region, and this effect became more pronounced with increasing relative roughness and Reynolds number. A similar effect could be seen by shortening the roughness spacing. An asymmetric distribution of rough elements decreased the entrance length compared with a symmetric distribution, which can be extrapolated to other irregularly distributed forms.

Reconstruction of numerical inlet boundary conditions using machine learning: Application to the swirling flow inside a conical diffuser

2021 ◽  
Vol 33 (8) ◽  
pp. 085132
Author(s):  
Pedro Véras ◽  
Guillaume Balarac ◽  
Olivier Métais ◽  
Didier Georges ◽  
Antoine Bombenger ◽  
...  
Keyword(s):  
Machine Learning ◽  
Boundary Conditions ◽  
Swirling Flow ◽  
Conical Diffuser

Nusselt Number as Composite Functions of Aspect Ratio and Wall Inclination in Parallelogram Microchannels with Three Types of Thermal Boundary Conditions

2016 ◽  
Vol 33 (4) ◽  
pp. 521-533 ◽  
Author(s):  
T.-M. Liou ◽  
H. Wang ◽  
S.-P. Chan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Boundary Conditions ◽  
Simple Algorithm ◽  
Working Fluid ◽  
Constant Wall Temperature ◽  
Time Saving ◽  
Thermal Boundary Conditions ◽  
Aspect Ratios ◽  
New Findings

AbstractIn this study, attention is focused on the numerical simulations of laminar fluid flow and heat transfer in straight smooth-walled parallelogram channels with various aspect ratios (α) and inclined angles (θ). The Reynolds number (Re), characterized by the channel hydraulic diameter and the working fluid of water, is fixed at 100. The examinedαandθrange from 1 to 10 and 45° to 90°, respectively. Their effects on the thermal fluid features are explored under three thermal boundary conditions: constant wall temperature (TBC), constant axial heat transfer rate with constant peripheral temperature (H1BC), and constant wall heat flux (H2BC). The SIMPLE algorithm is employed for velocity–pressure coupling with the algebraic multigrid method, while the second-order upwind scheme is utilized for spatial discretization in pressure term; the momentum and energy equations are solved with a QUICK scheme; Least Squares Cell-Based Gradient Evaluation is applied for predicting scalar values at the cell faces and for computing secondary diffusion terms and velocity derivatives. One of the new findings is that there exists a critical value ofθ= 70° below which the Nusselt number under H2BC increases with increasingαwhereas beyond which the trend reverses, a result distinct from those computed with TBC and H1BC. Moreover, TBC is found to be a time-saving alternative to H1BC. Furthermore, both Nusselt numbers under the three thermal boundary conditions and friction factor timesReare successfully and compactly correlated with α andθto offer useful reference for designing micro-cooling channels.

scholarly journals PIV-Measurements of Centrifugal Instabilities in a Rectangular Curved Duct with a Small Aspect Ratio

Fluids ◽  
2021 ◽  
Vol 6 (5) ◽  
pp. 184
Author(s):  
Afshin Goharzadeh ◽  
Peter Rodgers
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Velocity Distribution ◽  
Channel Wall ◽  
Secondary Flows ◽  
Working Fluid ◽  
Measured Velocity ◽  
Outer Channel ◽  
Dean Vortices ◽  
Curved Duct

In this study, experimental measurements were undertaken using non-intrusive particle image velocimetry (PIV) to investigate fluid flow within a 180° rectangular, curved duct geometry of a height-to-width aspect ratio of 0.167 and a curvature of 0.54. The duct was constructed from Plexiglas to permit optical access to flow pattern observations and flow velocity field measurements. Silicone oil was used as working fluid because it has a similar refractive index to Plexiglas. The measured velocity fields within the Reynolds number ranged from 116 to 203 and were presented at the curved channel section inlet and outlet, as well as at the mid-channel height over the complete duct length. It was observed from spanwise measurements that the transition to unsteady secondary flows generated the creation of wavy structures linked with the formation of Dean vortices close to the outer channel wall. This flow structure became unsteady with increasing Reynolds number. Simultaneously, the presence of Dean vortices in the spanwise direction influenced the velocity distribution in the streamwise direction. Two distinct regions defined by a higher velocity distribution were observed. Fluid particles were accelerated near the inner wall of the channel bend and subsequently downstream near the outer channel wall.

scholarly journals Slip Velocity Distribution in a Parallel Plate Channel on Asymmetric Thermal Boundary Condition

2016 ◽  
Vol 35 ◽  
pp. 113-126
Author(s):  
Md Tajul Islam
Keyword(s):  
Boundary Conditions ◽  
Velocity Distribution ◽  
Parallel Plate ◽  
Control Volume ◽  
Navier Stokes ◽  
Working Fluid ◽  
Slip Boundary Conditions ◽  
Cross Sectional ◽  
Slip Boundary ◽  
Knudsen Numbers

Steady, laminar and fully developed flows in parallel plate microchannel with asymmetric thermal wall conditions are solved by control volume technique. In order to examine the influence of Reynolds number and Knudsen number on the velocity distributions, a series of simulations are performed for different Reynolds and Knudsen numbers. Nitrogen gas is used as working fluid and we assume the fluid as continuum but employ the slip boundary conditions on the walls. The Navier-Stokes and energy equations are solved simultaneously. The results are found in good agreement with those predicted by analytical solutions in 2D continuous flow model employing first order slip boundary conditions. It is concluded that the rarefaction flattens the velocity distribution. If the product of Reynolds numbers and Knudsen numbers is fixed, the cross sectional average velocity is fixed for incompressible flow.GANIT J. Bangladesh Math. Soc.Vol. 35 (2015) 113-126

Effect of Surface Roughness on Aerodynamic Performance of Turbine Rear Structure

2019 ◽  
Author(s):  
Srikanth Deshpande ◽  
Isak Jonsson ◽  
Valery Chernoray
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Reynolds Number ◽  
Numerical Analysis ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Aerodynamic Performance ◽  
Axial Thrust ◽  
Low Pressure Turbine ◽  
Effect Of Surface

Abstract A turbine rear structure (TRS) is typically used to deswirl the flow from the low pressure turbine (LPT) and hence maximize the axial thrust. It is important to study the effect of surface roughness on aerodynamic performance of TRS. Numerical simulations with surface roughness are performed and results are compared with the data from experiments. Comparisons show that the trends between the numerical analysis and the experiments are in line with one another. Further understanding of numerical analysis shows that, at higher Reynolds number, the effect of surface roughness is more significant when compared to the effects at low-Reynolds number. An attempt has been made to study the transition behavior in the presence of surface roughness. Since boundary layer measurements are planned for the rig, this numerical study provides good inputs in order to plan instrumentation.

scholarly journals A New RANS Correction to Account for Varying Viscosity Effects

2021 ◽  
Author(s):  
Victor Coppo Leite ◽  
Elia Merzari
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Design Parameters ◽  
Working Fluid ◽  
Production Term ◽  
High Heat Transfer ◽  
Proposed Model ◽  
Varying Viscosity

Abstract It has previously been shown that by increasing the Reynolds number across a channel by spatially varying the viscosity does not cause an immediate change in the size of turbulent structures and a delay is in fact observed in both wall shear and friction Reynolds number (Coppo Leite, V, & Merzari, E., Proceedings of the ASME 2020 FEDSM, p. V003T05A019). Furthermore, it is also shown that depending on the length in which the flow condition changes, turbulence bursts are observed in the turbulence field. For the present work we propose a new version of the standard Reynolds Averaged Navier Stokes (RANS) k–τ model that includes some modifications in the production term in order to account for these effects. The new proposed model may be useful for many engineering applications as turbulent flows featuring temperature gradients and high heat transfer rates are often seen in heat exchangers, combustion chambers and nuclear reactors. In these applications, thermal and viscous properties of the working fluid are important design parameters that depend on temperature; hence it is likely to observe strong gradients on these scalars’ fields. To accomplish our goal, the modifications for the k–τ model are implemented and tested for a channel flow with spatial varying viscosity in the streamwise direction. The numerical simulations are performed using Nek5000, a spectral-element code developed at Argonne National Laboratory (ANL). Finally, the results considering a turbulence channel using the proposed model are compared against data obtained using Direct Numerical Simulations from the earlier work.

Swirling Flow of a Viscoelastic Fluid in a Cylindrical Casing

2005 ◽  
Vol 128 (1) ◽  
pp. 88-94 ◽  
Author(s):  
Motoyuki Itoh ◽  
Masahiro Suzuki ◽  
Takahiro Moroi
Keyword(s):  
Viscoelastic Fluid ◽  
Power Law ◽  
Velocity Component ◽  
Swirling Flow ◽  
Rotating Disk ◽  
Circumferential Velocity ◽  
Working Fluid ◽  
Velocity Measurements ◽  
Aspect Ratios ◽  
Cylindrical Casing

The swirling flow of a viscoelastic fluid in a cylindrical casing is investigated experimentally, using aqueous solutions of 0.05–1.0wt.% polyacrylamide as the working fluid. The velocity measurements are made using laser Doppler anemometer. The aspect ratios H∕R (H: axial length of cylindrical casing; R: radius of rotating disk) investigated are 2.0, 1.0, and 0.3. The Reynolds numbers Re0 based on the zero shear viscosity and the disk-tip velocity are between 0.36 and 50. The velocity measurements are mainly conducted for the circumferential velocity component. The experimental velocity data are compared to the velocity profiles obtained by numerical simulations using Giesekus model and power-law model. It is revealed that at any aspect ratios tested the dimensionless circumferential velocity component Vθ′ decreases with increasing Weissenberg number We. Both the Giesekus and power-law models could predict the retardation of circumferential velocity fairly well at small We. The extent of the inverse flow region, where the fluid rotates in the direction opposite to the rotating disk, is clarified in detail.

Sign in / Sign up

Export Citation Format

Share Document