Fully turbulent flows of viscoplastic fluids in a rectangular duct

Two-component stratified flow in a horizontal rectangular duct has been investigated experimentally. The working fluids were a transparent white mineral oil and water, the viscosity ratio being approximately 30. The tests encompassed a variety of flow regimes including laminar-laminar, laminar-turbulent, and turbulent-turbulent. In addition, a variety of conditions at the interface between the component flows was encountered and investigated. The experimental results for flow and pressure drop are found to be quite insensitive to the shape of the interface and even to the presence of very small waves, when both flow components are laminar. This finding extends the range of validity of flat-interface laminar flow theory. The conditions for the existence of various flow regimes are quantitatively characterized. It was demonstrated that interfacial waves could occur even when both component flows were laminar, and that laminar and turbulent flows could coexist in the separate layers. Results from depth-probe surveys and photographic visualization of the flow are also presented.

Download Full-text

Developing Heat Transfer and Friction in a Ribbed Rectangular Duct With Flow Separation at Inlet

Journal of Heat Transfer ◽

10.1115/1.2911319 ◽

1992 ◽

Vol 114 (3) ◽

pp. 565-573 ◽

Cited By ~ 40

Author(s):

Tong-Miin Liou ◽

Jenn-Jiang Hwang

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Turbulent Flows ◽

Local Heat Transfer ◽

Local Heat ◽

Equal Mass ◽

Rectangular Duct ◽

Entry Length ◽

A Value ◽

Semi Empirical

The local heat transfer and pressure drop characteristics of developing turbulent flows in a rectangular duct with an abrupt-contraction entrance and repeated square-rib pairs on the two opposite walls have been investigated experimentally. Both entrance-region and periodic-fully-developed-region results were obtained. Laser holographic interferometry was employed in the local and average heat transfer measurements. The Reynolds number was varied from 5.0 × 103 to 5.0 × 104; the rib pitch-to-height ratios were 10, 15, and 20; and the rib height-to-duct height ratio was kept at a value of 0.13. The results allowed the entry length to be determined and the regions susceptible to hot spots to be located. Semi-empirical heat transfer and friction correlations for the periodic fully developed region were developed. Moreover, performance comparisons between the ribbed and smooth ducts were made under two types of constraint, namely equal mass flow rate and equal pumping power. Finally, the effect of thermal entry length on the length mean Nusselt number was also investigated. The results showed that the length mean Nusselt number ratio was a function of only the duct length and independent of PR and Re, and could be further correlated by an equation of the form Num/Nup = 1 + 1.844/(X/De).

Download Full-text

Modified partially averaged Navier–Stokes model for turbulent flow in passages with large curvature

Modern Physics Letters B ◽

10.1142/s0217984920502395 ◽

2020 ◽

Vol 34 (23) ◽

pp. 2050239

Author(s):

Weixiang Ye ◽

Xianwu Luo ◽

Ying Li

Keyword(s):

Turbulent Flow ◽

Turbulent Flows ◽

Turbulence Model ◽

Navier Stokes ◽

Small Scale ◽

Bounded Region ◽

Rectangular Duct ◽

Reynolds Stresses ◽

Curvature Effects ◽

Text Model

This study presents a partially averaged Navier–Stokes model, MSST PANS, based on a modified SST [Formula: see text] turbulence model to predict turbulent flows with large streamline curvature. The model was validated for turbulent flow in a [Formula: see text] curved rectangular duct (Re = 224,000) to assess the MSST PANS capabilities. The predictions are compared against flow simulations for the same curved rectangular duct using four turbulence models including the standard [Formula: see text] model, SST [Formula: see text] model, [Formula: see text] PANS model and SST [Formula: see text] PANS model. Comparisons among those numerical results and available experimental data show that the MSST PANS model more accurately predicts the velocity components in all three directions, especially in the wall-bounded region than the other models. The study also shows the advantages of the MSST PANS model for predicting the Reynolds stresses, vorticity, and smaller scale turbulent structures in the wall-bounded region not only qualitatively but quantitatively. Furthermore, the MSST PANS model requires fewer computations than the SST PANS model, indicating that this turbulence model, which takes large streamlines curvature effects into consideration, is an effective alternative for capturing the small-scale turbulence flow structures. This turbulence model is expected to be very useful for engineering applications, especially for flows in turbomachinery.

Download Full-text

The Unsteady Boundary Layer in a Shock Tube

Proceedings of the Institution of Mechanical Engineers ◽

10.1243/pime_proc_1976_190_031_02 ◽

1976 ◽

Vol 190 (1) ◽

pp. 287-296 ◽

Cited By ~ 5

Author(s):

B. E. L. Deckker ◽

M. E. Weekes

Keyword(s):

Boundary Layer ◽

Shock Wave ◽

Turbulent Flows ◽

Three Dimensional ◽

Rectangular Duct ◽

Unsteady Boundary Layer ◽

High Quality ◽

Schlieren System ◽

Theoretical Predictions ◽

Laminar And Turbulent Flows

SYNOPSIS The unsteady boundary layer behind a moving shock wave in a rectangular duct 7.62 cm wide × 5.08 cm high has been studied using a high quality schlieren system. Growth of the boundary layer has been compared with the results of calculations for laminar and turbulent flows. The experimental results indicate that three dimensional effects are present which cause, in some cases, very early transition from laminar to turbulent flow. Agreement with theory is satisfactory only in the case of the weakest shock wave examined although the trends in growth rates generally conform to theoretical predictions.

Download Full-text

A Model for Calculating Turbulent Friction and Heat Transfer Coefficients of a Rectangular Duct With Angled Ribs on Two Opposite Walls

Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration ◽

10.1115/94-gt-183 ◽

1994 ◽

Author(s):

Le T. Tran

Keyword(s):

Heat Transfer ◽

Turbulent Flows ◽

Rectangular Duct ◽

Transfer Coefficients ◽

Turbulent Friction ◽

Circular Duct ◽

Law Of The Wall ◽

Heat Transfer Coefficients ◽

Rough Walls ◽

Wide Range

A new model is presented in this paper to calculate the pressure drop and the heat transfer coefficient for a rectangular duct with two smooth walls and two rough walls. Ribs on the rough walls may be at an angle with the main flow and are distributed in a repeated pattern. The model is based on the law-of-the-wall theory, which is known to give satisfactory results for turbulent flows in a circular duct or a channel, and for two-dimensional boundary layer flows. When the theory is applied to a rectangular duct, it gives simplified relationships between the friction, heat transfer coefficients, the flow Reynolds number, and geometry parameters, which include the rib angle, rib height, the rib pitch, and the duct aspect ratio. Comparisons with experimental data show that the present model gives satisfactory results for a wide range of Reynolds numbers and geometry parameters. A Prandtl number dependence is retained for applications involving fluids other than air.

Download Full-text

Symmetric and Asymmetric Turbulent Flows in a Rectangular Duct With a Pair of Ribs

Journal of Fluids Engineering ◽

10.1115/1.3243566 ◽

1988 ◽

Vol 110 (4) ◽

pp. 373-379 ◽

Cited By ~ 14

Author(s):

T.-M. Liou ◽

C.-F. Kao

Keyword(s):

Boundary Layer ◽

Reynolds Number ◽

Turbulent Flows ◽

Laser Doppler Velocimetry ◽

Boundary Layer Thickness ◽

Critical Reynolds Number ◽

Doppler Velocimetry ◽

Rectangular Duct ◽

Reattachment Length ◽

Mean Velocity

Laser-Doppler velocimetry (LDV) measurements are presented of mean velocity and turbulence intensity for turbulent flows past a pair of ribs in a rectangular duct of aspect ratio 2. The Reynolds number based on the duct hydraulic diameter was varied in the range of 2.0 × 103 to 7.6 × 104. The experiments cover ribs with rib height to duct height ratios from 0.13 to 0.33 and with rib width to height ratios from 1 to 10. The critical rib height above which and the critical Reynolds number below which the flow patterns become asymmetric were determined from the results. In addition, the effects of the rib width and boundary layer thickness on the formation and the size of the separation bubbles on the top surface of the ribs as well as on the reattachment length behind the ribs were documented. Furthermore, the degree of turbulence enhancement was compared between the asymmetric and the symmetric flows.

Download Full-text