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Article
Publication date: 20 June 2019

Mohamed Arif Raj Mohamed, Ugur Guven and Rajesh Yadav

The purpose of this paper is to achieve an optimum flow separation control over the airfoil using passive flow control method by introducing bio-inspired nose near the…

Abstract

Purpose

The purpose of this paper is to achieve an optimum flow separation control over the airfoil using passive flow control method by introducing bio-inspired nose near the leading edge of the NACA 2412 airfoil.

Design/methodology/approach

Two distinguished methods have been implemented on the leading edge of the airfoil: forward facing step, which induces multiple accelerations at low angle of attack, and cavity/backward facing step, which creates recirculating region (axial vortices) at high angle of attack.

Findings

The porpoise airfoil (optimum bio-inspired nose airfoil) delays the flow separation and improves the aerodynamic efficiency by increasing the lift and decreasing the parasitic drag. The maximum increase in aerodynamic efficiency is 22.4 per cent, with an average increase of 8.6 per cent at all angles of attack.

Research limitations/implications

The computational analysis has been done for NACA 2412 airfoil at low subsonic speed.

Practical implications

This design improves the aerodynamic performance and increases structural strength of the aircraft wing compared to other conventional high-lift devices and flow-control devices.

Originality/value

Different bio-inspired nose designs which are inspired by the cetacean species have been analysed for NACA 2412 airfoil, and optimum nose design (porpoise airfoil) has been found.

Details

Aircraft Engineering and Aerospace Technology, vol. 91 no. 7
Type: Research Article
ISSN: 1748-8842

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Article
Publication date: 11 January 2020

Adrián Vazquez Gonzalez, Andrés Meana-Fernández and Jesús Manuel Fernández

The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF…

Abstract

Purpose

The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan.

Design/methodology/approach

A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region.

Findings

It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes.

Research limitations/implications

Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy.

Originality/value

The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 10
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 30 October 2018

Jesús Manuel Fernandez Oro, Andrés Meana-Fernández, Monica Galdo Vega, Bruno Pereiras and José González Pérez

The purpose of this paper is the development of a CFD methodology based on LES computations to analyze the rotor–stator interaction in an axial fan stage.

Abstract

Purpose

The purpose of this paper is the development of a CFD methodology based on LES computations to analyze the rotor–stator interaction in an axial fan stage.

Design/methodology/approach

A wall-modeled large eddy simulation (WMLES) has been performed for a spanwise 3D extrusion of the central section of the fan stage. Computations were performed for three different operating conditions, from nominal (Q_N) to off-design (85 per cent Q_N and 70 per cent Q_N) working points. Circumferential periodic conditions were introduced to reduce the extent of the computational domain. The post-processing procedure enabled the segregation of unsteady deterministic features and turbulent scales. The simulations were experimentally validated using wake profiles and turbulent scales obtained from hot-wire measurements.

Findings

The transport of rotor wakes and both wake–vane and wake–wake interactions in the stator flow field have been analyzed. The description of flow separation, particularly at off-design conditions, is fully benefited from the LES performance. Rotor wakes impinging on the stator vanes generate a coherent large-scale vortex shedding at reduced frequencies. Large pressure fluctuations in the stagnation region on the leading edge of the vanes have been found.

Research limitations/implications

LES simulations have shown to be appropriate for the assessment of the design of an axial fan, especially for specific operating conditions for which a URANS model presents a lower performance for turbulence description.

Originality/value

This paper describes the development of an LES-based simulation to understand the flow mechanisms related to the rotor–stator interaction in axial fan stages.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 March 1993

SHIN FANN and WEN‐JEI YANG

A numerical study is performed to investigate flow instability phenomena in a square channel with steady, laminar throughflow. The channel rotates around an axis…

Abstract

A numerical study is performed to investigate flow instability phenomena in a square channel with steady, laminar throughflow. The channel rotates around an axis perpendicular to the channel longitudinal axis. The flow field extends from the channel entrance to a distance of 120 to 600Dh. The range of Reynolds number is Re = 300−2000. The inlet flow velocity is assumed uniform. Surface vorticity intensity is introduced to indicate the variation of vortices. It is revealed that at intermediate Reynolds numbers (680 > Re > 300), the flow is characterized by three vortex patterns: at slow rotation there is one vortex pair; at intermediate rotation a secondary vortex, in addition to the original vortex, emerges near the trailing wall and then breaks down downstream; and at rapid rotation the secondary vortex does not exist with the flow being restabilized to form a single‐pair vortex pattern. At low Reynolds numbers (Re ≤ 300), the flow exhibits a single‐pair vortex pattern, while at high Reynolds numbers (Re ≥ 680), the flow experiences the emergence and breakdown of a secondary vortex, but no restabilization is found with an increase in the rotational speed. It is also disclosed that the variation of the vortices is related to the distance from the inlet.

Details

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

Keywords

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Article
Publication date: 16 August 2019

Kaddour Touil and Adel Ghenaiet

The purpose of this paper is to characterize the blade–row interaction and investigate the effects of axial spacing and clocking in a two-stage high-pressure axial turbine.

Abstract

Purpose

The purpose of this paper is to characterize the blade–row interaction and investigate the effects of axial spacing and clocking in a two-stage high-pressure axial turbine.

Design/methodology/approach

Flow simulations were performed by means of Ansys-CFX code. First, the effects of blade–row stacking on the expansion performance were investigated by considering the stage interface. Second the axial spacing and the clocking positions between successive blade–rows were varied, the flow field considering the frozen interface was solved, and the flow interaction was assessed.

Findings

The axial spacing seems affecting the turbine isentropic efficiency in both design and off-design operating conditions. Besides, there are differences in aerodynamic loading and isentropic efficiency between the maximum efficiency clocking positions where the wakes of the first-stage vanes impinge around the leading edge of the second-stage vanes, compared to the clocking position of minimum efficiency where the ingested wakes pass halfway of the second-stage vanes.

Research limitations/implications

Research implications include understanding the effects of stacking, axial spacing and clocking in axial turbine stages, improving the expansion properties by determining the adequate spacing and locating the leading edge of vanes and blades in both first and second stages with respect to the maximum efficiency clocking positions.

Practical implications

Practical implications include improving the aerodynamic design of high-pressure axial turbine stages.

Originality/value

The expansion process in a two-stage high-pressure axial turbine and the effects of blade–row spacing and clocking are elucidated thoroughly.

Details

Aircraft Engineering and Aerospace Technology, vol. 91 no. 8
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 6 July 2015

Nader Pourmahmoud, Masoud Rashidzadeh and Amir Hassanzadeh

The purpose of this paper is to investigate the effect of convergent nozzles on the thermal separation inside a vortex tube, using a three-dimensional (3D) computational…

Abstract

Purpose

The purpose of this paper is to investigate the effect of convergent nozzles on the thermal separation inside a vortex tube, using a three-dimensional (3D) computational fluid dynamics (CFD) model as predicting tool.

Design/methodology/approach

The 3D finite volume formulation with the standard k-ε turbulence model has been used to carry out all the computations. Six different nozzles for convergence angle have been utilized β=0, 2, 4, 6, 8 and 10°. All other geometrical parameters were considered fixed at the experimental condition, i.e. main tube and chamber sizes and 294.2 K of gas temperature at inlets.

Findings

The numerical results present that there is an optimum convergence angle for obtaining the highest efficiency and β=2° is the optimal candidate under the simulations. It can be pointed that, some numerical data are validated by the available experimental results which show good agreement.

Practical implications

It is a useful and simple design of nozzle injectors to achieve the maximum cooling capacity.

Originality/value

In the work with assuming the advantages of using convergent nozzles on the energy separation and their considerable role on the creation of maximum cooling capacity of machine, the shape of nozzles was concentrated. This research believes that choosing an appropriate convergence angle is one of the important physical parameters. So far, an effective investigation toward the optimization of convergent nozzles has not been done but the importance of this subject can be regarded as an interesting research theme; so that the machine would operate in the way that the maximum cooling effect or the maximum refrigeration capacity is provided.

Details

Engineering Computations, vol. 32 no. 5
Type: Research Article
ISSN: 0264-4401

Keywords

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Article
Publication date: 7 March 2016

Frank Holzäpfel, Anton Stephan, Tobias Heel and Stephan Körner

From pilot reports, field measurements and numerical simulations, it is known that wake vortices may persist within the glide path in ground proximity, leading to an…

Abstract

Purpose

From pilot reports, field measurements and numerical simulations, it is known that wake vortices may persist within the glide path in ground proximity, leading to an increased encounter risk. This paper aims to investigate wake vortex behaviour during final approach and landing to understand why landings can be safe nevertheless. Further, it is investigated whether and to which extent the installation of plate lines beyond the runway tails may further accelerate wake vortex decay and thus improve safety by reducing the number of wake vortex encounters.

Design/methodology/approach

A hybrid numerical simulation approach is used to investigate vortex evolution from roll-up until final decay during the landing manoeuvre. The simulations are complemented by field measurement data accomplished at Munich Airport and at Special Airport Oberpfaffenhofen.

Findings

During touchdown, the so-called end effects trigger pressure disturbances and helical vortex structures that appear to ensure vortex decay rates in ground proximity needed to guarantee the required safety targets of aviation. Light detection and ranging (LIDAR) measurements indicate that vortex decay indeed can be accelerated by a plate line installed on the ground surface. The lifetime of the most safety relevant, long-lived and strongest vortices can be reduced by one-third.

Practical implications

The installation of plate lines beyond the runway tails may improve safety by reducing the number of wake vortex encounters and increase the efficiency of wake vortex advisory systems.

Originality/value

The novel numerical simulation technique and the acquired insights into the wake vortex phenomena occurring during landing as well as the demonstration of the functionality of the patented plate line provide high originality and value for both science and operational application.

Details

Aircraft Engineering and Aerospace Technology: An International Journal, vol. 88 no. 2
Type: Research Article
ISSN: 1748-8842

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Article
Publication date: 1 December 2002

S.Z. Shuja, B.S. Yilbas and M.O. Budair

The vortex shedding from a rectangular cylinder improves the heat transfer rates. Introducing a ground effect in such a flow system alters the shedding frequency, which in…

Abstract

The vortex shedding from a rectangular cylinder improves the heat transfer rates. Introducing a ground effect in such a flow system alters the shedding frequency, which in turn enables to vary the cooling rates of the cylinder. In the present study a laminar flow passing over a rectangular cylinder with a ground effect is considered. The flow and energy equations are solved numerically using a control volume approach. Strouhal and Stanton number variations due to gap height are computed and the influence of Strouhal number on Stanton number variation behind the cylinder is examined. The study is extended to include the predictions of entropy generation in the solution domain. It is found that shedding frequency increases as gap height reduces and further reduction in gap height results in diminishing of vortex shedding, in which case confined flow is developed in the gap. Heat transfer rates improve when Strouhal number is maximum. In the case of confined flow situation, heat transfer rates enhance substantially in the region close to the top corner of the cylinder, in which case, non‐uniform cooling of the surface is resulted.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 12 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 April 1992

SHIN FANN, WEN‐JEI YANG and S. MOCHIZUKI

A theoretical study is performed on three‐dimensional, heat transfer and fluid flow in radially rotating heated channels with steady, laminar throughflow. Consideration is…

Abstract

A theoretical study is performed on three‐dimensional, heat transfer and fluid flow in radially rotating heated channels with steady, laminar throughflow. Consideration is given to the channel of different geometry. Both the rotational speed and throughflow rate are varied. The flow is hydrodynamically and thermally developing, with a constant wall heat flux. The velocity‐vorticity method is employed in the formulation and numerical results are obtained by means of a finite‐difference technique. The Nusselt number, friction factor, and temperature and velocity distributions are determined, and the role of the Coriolis force on the entrance‐region transport phenomena is investigated. Results are compared with the existing literature.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 2 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 January 1986

J.I. Ramos

A mathematical model has been developed to study incompressible, isothermal, turbulent, confined, swirling flows. The model solves the conservation equations of mass…

Abstract

A mathematical model has been developed to study incompressible, isothermal, turbulent, confined, swirling flows. The model solves the conservation equations of mass, momentum, and two additional equations for the turbulent kinetic energy and the rate of dissipation of turbulent kinetic energy. The numerical predictions show a recirculation zone in the form of a one‐celled toroidal vortex at the combustor centreline. High levels of turbulence characterize the recirculation zone. The length, diameter and maximum velocity of the recirculation zone first decrease and then increase as the magnitude of the outer swirl number is first decreased from counter‐swirl to zero and then increased to co‐swirl flow conditions. Counter‐swirl produces steeper velocity gradients at the inter‐jet shear layer and promotes faster mixing than co‐swirl. The numerical results also indicate that the mass of the recirculation zone first decreases and then increases as the outer swirl number is first decreased from counter‐swirl to zero and then increased to co‐swirl conditions. The diameter, maximum velocity and mass of the recirculation zone are monotonically increasing functions of the inner jet swirl number. The recirculation zone length, diameter and mass are almost independent of the Reynolds number and outer‐to‐inner jet axial velocity ratio.

Details

Engineering Computations, vol. 3 no. 1
Type: Research Article
ISSN: 0264-4401

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