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Article
Publication date: 1 June 2006

Gong Hee Lee and Je Hyun Baek

To investigate the effect of aspect ratio on the quantitative analogy between developing laminar flows in orthogonally rotating straight ducts and stationary curved ducts

Abstract

Purpose

To investigate the effect of aspect ratio on the quantitative analogy between developing laminar flows in orthogonally rotating straight ducts and stationary curved ducts

Design/methodology/approach

A fractional step method is used to obtain the numerical solution of the governing equations by decoupling the solution of the momentum equations from the solution of the continuity equation. In order to clarify the similarity of the two flows, dimensionless parameters KLR and Rossby number, Ro, in a rotating straight duct were used as a set corresponding to Dean number, KLC, and curvature ratio, λ, in a stationary curved duct.

Findings

Under the condition that the aspect ratio was larger than one and that the magnitude of Ro or λ was large enough to satisfy the “asymptotic invariance property” the quantitative analogy between the two flows was established clearly.

Research limitations/implications

As the aspect ratio decreased below one, the difference between the secondary flow intensities of these two flows increased, and therefore, the analogy between the two flows was not as evident as that for the larger aspect ratios.

Practical implications

Based on this methodology, the characteristics of the developing flow in orthogonally rotating ducts of higher aspect ratio can be predicted by considering the flow in stationary curved ducts, and vice versa.

Originality/value

The results obtained in this study will suggest an optimal criterion for the application of this approach to the flow similarity analysis in rectangular ducts with arbitrary aspect ratios.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 16 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 May 2002

Gong Hee Lee and Je Hyun Baek

A numerical study of a quantitative analogy of fully developed turbulent flow in a straight square duct rotating about an axis perpendicular to that of the duct and a stationary…

Abstract

A numerical study of a quantitative analogy of fully developed turbulent flow in a straight square duct rotating about an axis perpendicular to that of the duct and a stationary curved duct of square cross‐section was carried out. In order to compare the two flows, the dimensionless parameters KTR=Re1/4/√Ro and the Rossby number, Ro=wmdh, in the rotating straight duct flow corresponded to KTC=Re1/4/√λ and the curvature ratio, λ=R/dh, in the stationary curved duct flow, so that they had the same dynamical meaning as those parameters for fully developed laminar flow. For the large values of Ro or λ, the flow field satisfied the “asymptotic invariance property”; there were strong quantitative similarities between the two flows, such as in the flow patterns and friction factors for the same values of KTR and KTC. Based on these similarities, it is possible to predict the flow characteristics in rotating ducts by considering the flow in stationary curved ducts, and vice versa.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 12 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 12 October 2012

Fotios Papadopoulos, Ioannis Valakos and Ioannis K. Nikolos

The purpose of this paper is to design an S‐duct intake for unmanned aerial vehicles (UAVs) applications with good efficiency in a wide range of operating conditions.

Abstract

Purpose

The purpose of this paper is to design an S‐duct intake for unmanned aerial vehicles (UAVs) applications with good efficiency in a wide range of operating conditions.

Design/methodology/approach

A fully‐parametric 3‐D CAD model of the intake was constructed in order to produce different intake configurations, within specific geometric constraints, and to study the influence of geometry variation on efficiency. O‐type blocking methodology was adopted in order to construct the block‐structured mesh of hexahedral elements, used in the simulations. The commercial CFD code ANSYS‐CFX was used to compute the flow field inside the flow domain of each case considered. The Reynolds averaged Navier‐Stokes (RANS) equations are discretized using an implicit, vertex‐based finite volume method, combined with the shear stress transport (SST) two‐equation turbulence model and an automatic wall treatment.

Findings

By shortening the axial length the flow separation after the first turning becomes more pronounced and the losses are increasing. For very long ducts the increased internal wall area leads to increased wall friction and, consequently, to increased loss production.

Originality/value

The adoption of Gerlach‐shaped profiles for the design of the S‐duct resulted in a low pressure loss level for the optimal shape, although more uniform distribution of total pressure losses resulted for ducts longer than the optimal one, which should be taken into account in the design process.

Details

Aircraft Engineering and Aerospace Technology, vol. 84 no. 6
Type: Research Article
ISSN: 0002-2667

Keywords

Article
Publication date: 1 September 2000

Jenn Jiang Hwang and Wei‐Jyh Wang

Deals with the flow reversal in a buoyancy‐opposed rotating duct that causes heat transfer deterioration. An active technique of trailing‐wall transpiration is adopted to check…

Abstract

Deals with the flow reversal in a buoyancy‐opposed rotating duct that causes heat transfer deterioration. An active technique of trailing‐wall transpiration is adopted to check whether it can avoid the flow separation and subsequently improves the heat transfer deterioration. Finite‐difference method is employed to solve the three‐dimensional Navier‐Stokes equations and the energy equation. Periodic conditions are used between the entrance and exit of a typical two‐pass duct for the closure of the elliptic problem. The predicted results reveal that fluid withdrawal through the trailing wall can avoid the flow separation from the leading wall of the radial‐outward duct (ROD) and thus eliminate local hot spots. In addition, the trailing‐wall suction not only increases the peripherally averaged heat transfer but also reduces the friction loss in the ROD. In the radial‐inward duct (RID), both the peripherally averaged heat transfer and peripherally averaged friction factor are augmented by trailing‐wall injection and are degraded by the trailing‐wall suction.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 10 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 15 July 2021

Yang Liu, Qingwei Gong, Yongning Bian and Qinghui Suo

Hydrodynamic forces and efficiency of bare propeller and ducted propellers with a wide range of advance ratio (J) and attack angle (θ) are examined. The thrust and torque…

Abstract

Purpose

Hydrodynamic forces and efficiency of bare propeller and ducted propellers with a wide range of advance ratio (J) and attack angle (θ) are examined. The thrust and torque coefficients and the efficiency are presented and discussed in detail. The present results give a reliable guidance to the improvement of the hydrodynamic characteristics of ducted propellers.

Design/methodology/approach

The effect of a duct on the hydrodynamic performance of the KP458 propeller is numerically investigated in this study. Finite volume method (FVM)-based simulations are performed for a wide range of advance ratio J (0 ≤ J ≤ 0.75) and attack angle θ of the duct (15° ≤ θ ≤ 45°). A cubic computational domain is employed in this study, and the moving reference frame (MRF) approach is adopted to handle the rotation of the propeller. Turbulence is accounted for with the RNG k-ε model. The present numerical results are first compared against available experimental data and a good agreement is achieved.

Findings

The simulation results demonstrate that the hydrodynamic forces and efficiency increases and decreases with J, respectively, at the same attack angle. In addition, it is demonstrated that the hydrodynamic forces and efficiency are both improved due to the presence of the duct, which eventually leads a better hydrodynamic performance at high advance ratios. It is further revealed that as the attack angle increases, the pressure difference between the suction- and pressure-surfaces of the propeller is also augmented, which results in a larger thrust. The wake field is more uniform at θ = 30°, suggesting that a higher efficiency can be obtained.

Originality/value

The present study aims to investigate the effect of a duct on the KP458 propeller subjected to uniform inbound flow. The relationship between the uniform incoming flow and the attack angle of the duct is mainly focused, and the design of the ducted propellers for any ship hull can be improved according to this relationship.

Details

Engineering Computations, vol. 39 no. 2
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 September 2000

Esa Utriainen and Bengt Sundén

A three‐dimensional numerical study was conducted to assess the hydraulic and heat transfer performance of a primary surface type heat exchanger surface, called the trapezoidal…

Abstract

A three‐dimensional numerical study was conducted to assess the hydraulic and heat transfer performance of a primary surface type heat exchanger surface, called the trapezoidal cross wavy (TCW) duct. This duct is similar to the ducts being used in compact recuperators manufactured by Solar Turbines Inc. The governing equations, i.e. the mass conservation equation, Navier‐Stokes equations and the energy equation, are solved numerically by a finite volume method for boundary fitted coordinates. Periodic boundary conditions are imposed in the main flow direction. In this particular case laminar convective flow and heat transfer prevail. Owing to the complex geometry a complicated secondary flow pattern appears in the cross‐sectional planes. Details of the recuperator ducts and the numerical method, as well as relevant results, are presented. The overall results are also compared with corresponding results (i.e. Nu numbers, friction factors) of straight ducts with various cross‐sectional shapes.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 10 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 June 2001

Jung‐Chul Shin

The potential flow field for the transitional region in a constant radius, two‐dimensional duct was studied. The potential velocity and pressure profiles in various duct

Abstract

The potential flow field for the transitional region in a constant radius, two‐dimensional duct was studied. The potential velocity and pressure profiles in various duct geometries with different turning angles and duct heights were investigated. A generalized solution of potential flow in a transitional bend was obtained.

Details

Aircraft Engineering and Aerospace Technology, vol. 73 no. 3
Type: Research Article
ISSN: 0002-2667

Keywords

Article
Publication date: 1 July 1996

T. BO and H. IACOVIDES

This article examines the influence of centrifugal buoyancy on the hydrodynamic and thermal behaviour in fully developed flow through an orthogonally rotating duct of aspect ratio…

Abstract

This article examines the influence of centrifugal buoyancy on the hydrodynamic and thermal behaviour in fully developed flow through an orthogonally rotating duct of aspect ratio 2:1. A series of computations have been performed at rotation numbers ranging from 0 to 0.2, for constant‐density flows (no buoyancy) and also for different levels of outward and inward buoyancy. The resulting comparisons reveal that for a Reynolds number of 32,500, rotational buoyancy effects become significant at Rayleigh number values greater than 107. In outward flows, buoyancy is found to strengthen the effects of the Coriolis force on the mean motion and, by raising turbulence levels, buoyancy also enhances wall heat transfer along both the pressure and the suction side of the rotating duct. In inward flows, it is found that strong buoyancy can reverse the direction of the Coriolis‐induced secondary motion, which causes a strong rise in wall heat transfer along the suction side and a similarly significant fall in heat transfer along the pressure side. The computed effects on heat transfer are in qualitative agreement with the findings of a number of experimental studies. For both inward and outward flows, at a constant Reynolds number, the modifications of centrifugal buoyancy on the side‐averaged levels of heat transfer correlate reasonably well with the rotational Rayleigh number.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 6 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 16 April 2018

Eero Immonen

This paper aims to design an optimal shape for an annular S-duct, considering both energy losses and exit flow uniformity, starting from a given baseline design. Moreover, this…

Abstract

Purpose

This paper aims to design an optimal shape for an annular S-duct, considering both energy losses and exit flow uniformity, starting from a given baseline design. Moreover, this paper seeks to identify the design factors that affect the optimal annular S-duct designs.

Design/methodology/approach

The author has carried out computational fluid dynamic (CFD)-based shape optimization relative to five distinct numerical objectives, to understand their interrelations in optimal designs. Starting from a given baseline S-duct design, they have applied control node-induced shape deformations and high-order polynomial response surfaces for modeling the functional relationships between the shape variables and the numerical objectives. A statistical correlation analysis is carried out across the optimal designs.

Findings

The author has shown by single-objective optimization that the two typical goals in S-duct design, energy loss minimization and exit flow uniformity, are mutually contradictory. He has presented a multi-objective solution for an optimal shape, reducing the total pressure loss by 15.6 per cent and the normalized absolute radial exit velocity by 34.2 per cent relative to a baseline design. For each of the five numerical objectives, the best optimization results are obtained by using high-order polynomial models.

Research limitations/implications

The methodology is applicable to axisymmetric two-dimensional geometry models.

Originality/value

This paper applies a recently introduced shape optimization methodology to annular S-ducts, and, it is, to the author’s knowledge, the first paper to point out that the two widely studied design objectives for annular S-ducts are contradictory. This paper also addresses the value of using high-order polynomial response surface models in CFD-based shape optimization.

Details

Engineering Computations, vol. 35 no. 2
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 1 January 2014

Tareq Salameh and Bengt Sunden

– The aim of this paper is to study two-dimensional numerical simulations of the flow and temperature fields inside the bend (turn) part of a U-duct.

Abstract

Purpose

The aim of this paper is to study two-dimensional numerical simulations of the flow and temperature fields inside the bend (turn) part of a U-duct.

Design/methodology/approach

Several turbulence models based on two and five equations were used to solve the momentum and energy equations inside the bend (turn) part of the U-duct. For two-equation models, both the renormalization group and realizable k-ɛ turbulence models were implemented. The five-equation model used is a Reynolds stress model with different wall boundary conditions. Standard, non-equilibrium and enhanced wall functions were used in parallel with the two- and five-equation models to treat the turbulent flow near the duct walls.

Findings

Several turbulence models were used to simulate the flow and temperature fields along the bend part of a U-duct with different inlet and thermal boundary conditions. The numerical results indicate that the renormalization and realizable k-ɛ turbulence models with standard wall function treatment gave the best results when compared with experimental data obtained for similar conditions.

Research limitations/implications

For heat transfer analysis, two different thermal boundary conditions, i.e. constant wall temperature and constant heat flux at the wall are implemented. The results are calculated for Reynolds number equal 20,000.

Practical implications

The results can be used in designing heat exchangers, piping and duct systems, and internal passage cooling of gas turbine blades.

Originality/value

The numerical results obtained here concentrate on the detailed investigation of flow and temperature field at the outer wall of the bend part. Different boundary conditions at the inlet and the outer bend walls of the U-duct were applied to study how these boundary conditions affect the flow and temperature fields.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 24 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

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