Direct Numerical Simulation of Turbulent Flow and Heat Transfer in a Square Duct Roughened with Transverse Or V-shaped Ribs

Direct Numerical Simulation of Turbulent Flow and Heat Transfer in a Square Duct Roughened with Transverse Or V-shaped Ribs
Author: Seyyed Vahid Mahmoodi Jezeh
Publisher:
Total Pages: 0
Release: 2021
Genre:
ISBN:
GET BOOK

Download Direct Numerical Simulation of Turbulent Flow and Heat Transfer in a Square Duct Roughened with Transverse Or V-shaped Ribs Book in PDF, Epub and Kindle

This integrated thesis documents a series of complementary numerical investigations aimed at an improved understanding of turbulent flows and heat transfer in a square duct with ribs of different shapes mounted on one wall. Direct numerical simulation (DNS) is used to accurately resolve the spatial and temporal scales of the simulated flows. The first DNS investigates the turbulent flow in a ribbed square duct of different blockage ratios. The results are compared with those of a smooth duct flow. It is observed that an augmentation of the blockage ratio concurrently generates stronger turbulent secondary flow motions, which drastically alter the turbulent transport processes between the sidewall and duct center, giving rise to high-degrees of non-equilibrium states. The dynamics of coherent structures are studied by examining characteristics of the instantaneous velocity field, swirling strength, spatial two-point auto-correlations, and velocity spectra. The impact of the blockage ratio on the turbulent heat transfer is investigated in the second numerical study. The results show that owing to the existence of the ribs and confinement of the duct, organized secondary flows appear as large streamwise-elongated vortices, which have profound influences on the transport of momentum and thermal energy. This study also shows that the spatial distribution and magnitude of the drag and heat transfer coefficients are highly sensitive to the rib height. The final study focuses on a comparison of highly-disturbed turbulent flows in a square duct with inclined and V-shaped ribs mounted on one wall. The turbulence field is highly sensitive to not only the rib geometry but also the boundary layers developed over the side and top walls. Owing to the difference in the pattern of the cross-stream secondary flow motions of these two ribbed duct cases, the flow physics in the inclined rib case is significantly different from the V-shaped rib case. It is found that near the leeward and windward faces of the ribs, the mean inclination angle of turbulence structures in the V-shaped rib case is greater than that of the inclined rib case, which subsequently enhances momentum transport between the ribbed bottom wall and the smooth top wall.

Direct Numerical Simulation of Turbulent Flow and Heat Transfer in a Square Duct at Low Reynolds Number

Direct Numerical Simulation of Turbulent Flow and Heat Transfer in a Square Duct at Low Reynolds Number
Author: M. Piller
Publisher:
Total Pages: 8
Release: 2001
Genre:
ISBN:
GET BOOK

Download Direct Numerical Simulation of Turbulent Flow and Heat Transfer in a Square Duct at Low Reynolds Number Book in PDF, Epub and Kindle

In this paper, we present the results from Direct Numerical Simulations of turbulent, incompressible flow through a square duct, with an imposed temperature difference between two opposite walls, while the other two walls are assumed perfectly insulated. The mean flow is sustained by an imposed, mean pressure gradient. The most interesting feature, characterizing this geometry, consists in the presence of turbulence-sustained mean secondary motions in the cross-flow plane. In this study, we focus on weak turbulence, in that the Reynolds number, based on bulk velocity and hydraulic diameter, is about 4450. Our results indicate that secondary motions do not affect dramatically the global parameters, like friction factor and Nusselt number, in comparison with the plane-channel flow. This issue is investigated by looking at the distribution of the various contributions to the total heat flux, with particular attention to the mean convective term, which does not appear in the plane channel flow.

The Influences of V-shaped Ribs and Spanwise System Rotation on a Turbulent Square Duct Flow

The Influences of V-shaped Ribs and Spanwise System Rotation on a Turbulent Square Duct Flow
Author: Xingjun Fang
Publisher:
Total Pages: 0
Release: 2015
Genre:
ISBN:
GET BOOK

Download The Influences of V-shaped Ribs and Spanwise System Rotation on a Turbulent Square Duct Flow Book in PDF, Epub and Kindle

In this thesis, the effects of surface-mounted V-shaped ribs and spanwise system rotations on fully-developed turbulent square duct flows were investigated using the particle image velocimetry (PIV) measurement, large-eddy simulation (LES) and direct numerical simulation (DNS). The PIV measurements were conducted in a water channel, and three different angled V-shaped (60°, 45° and 30°) and perpendicular (90°) ribs were considered. As a complement for the PIV experiments, LES was also used to simulate the measured cases under the same experimental conditions. To perform LES, a parallel finite volume method (FVM) code adopting the generalized curvilinear coordinate system was developed. The first- and second-order moments of the turbulence flows obtained from LES were validated against the PIV measurement data. Both the PIV and LES results showed that strong secondary flows in the pattern of a pair of counter-rotating streamwise-elongated vortices exist in all three V-shaped rib cases. The impacts of rib geometry on turbulent coherent structures were investigated using vortex identifiers, temporal autocorrections, spatial two-point autocorrelations, and velocity spectra. To study the effects of system rotations on turbulent square duct flows, DNS was performed for the turbulent flows confined within a square duct subjected to at a wide range of spanwise system rotations. The DNS was conducted using a modified open-source parallel spectral-element method (SEM) code. The influences on turbulent duct flows by the system rotation were investigated by analyzing the transport equations of Reynolds stresses and vorticity correlations. Turbulent structures under different system rotations were also systematically studied using the energy spectra, autocorrelations of vorticity fluctuations, and linear stochastic estimation. It was observed that in response to the system rotation, secondary flows appear as streamwise counter-rotating vortices. At sufficiently high rotation numbers, a Taylor-Proudman region appears and complete laminarization is almost reached near the top and sidewalls. It was also observed that the Coriolis force dominates the transport of Reynolds stresses and turbulent kinetic energy, and forces the spectra of streamwise and vertical velocities to synchronize within a wide range of streamwise length scales.

Journal of Thermophysics and Heat Transfer

Journal of Thermophysics and Heat Transfer
Author:
Publisher:
Total Pages: 996
Release: 2006
Genre: Heat
ISBN:
GET BOOK

Download Journal of Thermophysics and Heat Transfer Book in PDF, Epub and Kindle

This journal is devoted to the advancement of the science and technology of thermophysics and heat transfer through the dissemination of original research papers disclosing new technical knowledge and exploratory developments and applications based on new knowledge. It publishes papers that deal with the properties and mechanisms involved in thermal energy transfer and storage in gases, liquids, and solids or combinations thereof. These studies include conductive, convective, and radiative modes alone or in combination and the effects of the environment.

Applied Mechanics Reviews

Applied Mechanics Reviews
Author:
Publisher:
Total Pages: 338
Release: 1987
Genre: Mechanics, Applied
ISBN:
GET BOOK

Download Applied Mechanics Reviews Book in PDF, Epub and Kindle

Gas Turbine Heat Transfer and Cooling Technology, Second Edition

Gas Turbine Heat Transfer and Cooling Technology, Second Edition
Author: Je-Chin Han
Publisher: CRC Press
Total Pages: 892
Release: 2012-11-27
Genre: Science
ISBN: 1439855684
GET BOOK

Download Gas Turbine Heat Transfer and Cooling Technology, Second Edition Book in PDF, Epub and Kindle

A comprehensive reference for engineers and researchers, Gas Turbine Heat Transfer and Cooling Technology, Second Edition has been completely revised and updated to reflect advances in the field made during the past ten years. The second edition retains the format that made the first edition so popular and adds new information mainly based on selected published papers in the open literature. See What’s New in the Second Edition: State-of-the-art cooling technologies such as advanced turbine blade film cooling and internal cooling Modern experimental methods for gas turbine heat transfer and cooling research Advanced computational models for gas turbine heat transfer and cooling performance predictions Suggestions for future research in this critical technology The book discusses the need for turbine cooling, gas turbine heat-transfer problems, and cooling methodology and covers turbine rotor and stator heat-transfer issues, including endwall and blade tip regions under engine conditions, as well as under simulated engine conditions. It then examines turbine rotor and stator blade film cooling and discusses the unsteady high free-stream turbulence effect on simulated cascade airfoils. From here, the book explores impingement cooling, rib-turbulent cooling, pin-fin cooling, and compound and new cooling techniques. It also highlights the effect of rotation on rotor coolant passage heat transfer. Coverage of experimental methods includes heat-transfer and mass-transfer techniques, liquid crystal thermography, optical techniques, as well as flow and thermal measurement techniques. The book concludes with discussions of governing equations and turbulence models and their applications for predicting turbine blade heat transfer and film cooling, and turbine blade internal cooling.

Direct Numerical Simulation of Turbulent Flows in a Rectangular Duct of Different Aspect Ratios

Direct Numerical Simulation of Turbulent Flows in a Rectangular Duct of Different Aspect Ratios
Author: Jiaxin Yan
Publisher:
Total Pages: 0
Release: 2018
Genre:
ISBN:
GET BOOK

Download Direct Numerical Simulation of Turbulent Flows in a Rectangular Duct of Different Aspect Ratios Book in PDF, Epub and Kindle

Direct numerical simulations are performed to investigate turbulent flows in a rectangular duct of aspect ratio varying from 1.0 to 3.0 at a fixed low Reynolds number 150. Persistent secondary flows of Prandtl's second kind are observed in the corners of the ducts. As the aspect ratio increases, streamwise vortices near the top and bottom walls extend towards to the central vertical plane of ducts. Particularly, the displacement of vortex cores near the top/bottom wall can be described as a function of the distance to the sidewall. Detailed analyses of turbulence statistics including the mean flow, turbulent kinetic energy, turbulent intensities, Reynolds stress budgets, and pre-multiplied one-dimensional energy spectrum are conducted to understand the aspect ratio effects on the flow physics. In the duct of aspect ratio 3.0, hairpin flow structures are present in the central regions of the duct, and their characteristics are similar to those exhibited in the plane channel flows. Furthermore, as indicated by the energy spectra, a spanwise quasi-homogeneous region spans over approximately 270 wall units in the central region of the rectangular duct.