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Article
Publication date: 11 July 2019

Van Luc Nguyen, Tomohiro Degawa and Tomomi Uchiyama

This paper aims to provide discussions of a numerical method for bubbly flows and the interaction between a vortex ring and a bubble plume.

Abstract

Purpose

This paper aims to provide discussions of a numerical method for bubbly flows and the interaction between a vortex ring and a bubble plume.

Design/methodology/approach

Small bubbles are released into quiescent water from a cylinder tip. They rise under the buoyant force, forming a plume. A vortex ring is launched vertically upward into the bubble plume. The interactions between the vortex ring and the bubble plume are numerically simulated using a semi-Lagrangian–Lagrangian approach composed of a vortex-in-cell method for the fluid phase and a Lagrangian description of the gas phase.

Findings

A vortex ring can transport the bubbles surrounding it over a distance significantly depending on the correlative initial position between the bubbles and the core center. The motion of some bubbles is nearly periodic and gradually extinguishes with time. These bubble trajectories are similar to two-dimensional-helix shapes. The vortex is fragmented into multiple regions with high values of Q, the second invariant of velocity gradient tensor, settling at these regional centers. The entrained bubbles excite a growth rate of the vortex ring's azimuthal instability with a formation of the second- and third-harmonic oscillations of modes of 16 and 24, respectively.

Originality/value

A semi-Lagrangian–Lagrangian approach is applied to simulate the interactions between a vortex ring and a bubble plume. The simulations provide the detail features of the interactions.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 9
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 11 February 2019

Van Luc Nguyen, Tomohiro Degawa and Tomomi Uchiyama

This study aims to provide discussions of the numerical method and the bubbly flow characteristics of an annular bubble plume.

Abstract

Purpose

This study aims to provide discussions of the numerical method and the bubbly flow characteristics of an annular bubble plume.

Design/methodology/approach

The bubbles, released from the annulus located at the bottom of the domain, rise owing to buoyant force. These released bubbles have diameters of 0.15–0.25 mm and satisfy the bubble flow rate of 4.1 mm3/s. The evolution of the three-dimensional annular bubble plume is numerically simulated using the semi-Lagrangian–Lagrangian (semi-LL) approach. The approach is composed of a vortex-in-cell method for the liquid phase and a Lagrangian description of the gas phase.

Findings

First, a new phenomenon of fluid dynamics was discovered. The bubbly flow enters a transition state with the meandering motion of the bubble plume after the early stable stage. A vortex structure in the form of vortex rings is formed because of the inhomogeneous bubble distribution and the fluid-surface effects. The vortex structure of the flow deforms as three-dimensionality appears in the flow before the flow fully develops. Second, the superior abilities of the semi-LL approach to analyze the vortex structure of the flow and supply physical details of bubble dynamics were demonstrated in this investigation.

Originality/value

The semi-LL approach is applied to the simulation of the gas–liquid two-phase flows.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 May 1956

P.R. Payne

ALL the theories relating to the nature of the airflow through a helicopter rotor which have been reviewed in the first three parts of this paper relate to vertical…

Abstract

ALL the theories relating to the nature of the airflow through a helicopter rotor which have been reviewed in the first three parts of this paper relate to vertical velocities only; that is, to the downwards acceleration of the air whereby rotor thrust is generated. But since a practical rotor blade also experiences in‐plane forces it is evident that in‐plane movements of the air in the slipstream must also occur. In point of fact the slipstream rotation behind the propeller of a single engined aeroplane of conventional design is an important factor in its design, particularly when considering take‐off conditions.

Details

Aircraft Engineering and Aerospace Technology, vol. 28 no. 5
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 24 February 2020

Yadav Krishna Kumar Rajnath, Akshoy Ranjan Paul and Anuj Jain

The purpose of air-intake duct used in combat aircrafts is to decelerate the inlet flow and concurrently raise the static pressure recovery at the compressor inlet…

Abstract

Purpose

The purpose of air-intake duct used in combat aircrafts is to decelerate the inlet flow and concurrently raise the static pressure recovery at the compressor inlet. Because of side-slip movement during sharp maneuvers of the aircrafts, the airflows ingested into twin air-intake ducts are not same and symmetric at its two inlets but are asymmetric in nature. The asymmetric inlet flow conditions at the twin air-intakes thus caused instabilities and deteriorated aerodynamic performance of aircraft components such as compressors and other downstream components. This study aims to investigate the flow control in a twin air-intake with asymmetric inflows.

Design/methodology/approach

The continuity and momentum equations are solved with second-order upwind scheme for computing finite-volume method-based unsteady computational fluid dynamics simulation.

Findings

Performance parameters are deteriorated with the increase of inflow asymmetry in the twin air-intake duct. Slotted synthetic jets are used to manage flow separation, thereby increasing aerodynamic performance of the air-intake. A variety of vortical structures are generated from the rectangular slots, convected downstream of the twin air-intake. The use of slotted synthetic jets increases static pressure recovery by 64 per cent whereas reducing total pressure loss coefficient by 63 per cent, distortion coefficient by 58 per cent and swirl coefficient by 55 per cent which is an indicative of better aerodynamic performance of twin air-intake.

Originality/value

The study stresses the need of robust flow control technique to improve the performance of combat air-intake system under extreme maneuvering conditions. The results can be useful in designing air-intake satisfying the stealth features for modern combat aircrafts.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 3
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 1 February 1940

J.A.J. Bennett

THAT the rotaplane rotor is essentially a windmill has hitherto been regarded as self‐evident. It will be shown in the following analysis that, when the profile drag is…

Abstract

THAT the rotaplane rotor is essentially a windmill has hitherto been regarded as self‐evident. It will be shown in the following analysis that, when the profile drag is sufficiently small, only part of the rotor is in the “windmill brake” state. This part receives more torque from the air than can be expended in profile drag and therefore the rotaplane rotor at zero torque must be partly an airscrew in the “vortex ring” state.

Details

Aircraft Engineering and Aerospace Technology, vol. 12 no. 2
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 June 1949

W.J. Duncan

THE paper reviews the problem of the influence of the walls of a closed tunnel in increasing the velocity in the neighbourhood of a model under test. It is shown that, for…

Abstract

THE paper reviews the problem of the influence of the walls of a closed tunnel in increasing the velocity in the neighbourhood of a model under test. It is shown that, for a perfect fluid, considerations of continuity suffice to establish an exact value of the mean interference velocity for any cross‐section of the tunnel. This mean interference velocity is expressed in terms of the perturbation velocity which would be caused by the same model in the absence of the walls. The linearized theory of subsonic compressible flow is applied and it is shown that the interference velocity for a small two or three dimensional model is increased in proportion to l/β3, where β=√(l—M2) and M is the Mach number. Interference caused by a body with a long parallel middle body, the influence of the wake from a model and of the boundary layer on the tunnel walls are briefly considered.

Details

Aircraft Engineering and Aerospace Technology, vol. 21 no. 6
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 10 December 2019

Eric Goncalves Da Silva and Philippe Parnaudeau

The purpose of this paper is to quantify the relative importance of the multiphase model for the simulation of a gas bubble impacted by a normal shock wave in water. Both…

Abstract

Purpose

The purpose of this paper is to quantify the relative importance of the multiphase model for the simulation of a gas bubble impacted by a normal shock wave in water. Both the free-field case and the collapse near a wall are investigated. Simulations are performed on both two- and three-dimensional configurations. The main phenomena involved in the bubble collapse are illustrated. A focus on the maximum pressure reached during the collapse is proposed.

Design/methodology/approach

Simulations are performed using an inviscid compressible homogeneous solver based on different systems of equations. It consists in solving different mixture or phasic conservation laws and a transport-equation for the gas volume fraction. Three-dimensional configurations are considered for which an efficient massively parallel strategy was developed. The code is based on a finite volume discretization for which numerical fluxes are computed with a Harten, Lax, Van Leer, Contact (HLLC) scheme.

Findings

The comparison of three multiphase models is proposed. It is shown that a simple four-equation model is well-suited to simulate such strong shock-bubble interaction. The three-dimensional collapse near a wall is investigated. It is shown that the intensity of pressure peaks on the wall is drastically increased (more than 200 per cent) in comparison with the cylindrical case.

Research limitations/implications

The study of bubble collapse is a key point to understand the physical mechanism involved in cavitation erosion. The bubble collapse close to the wall has been addressed as the fundamental mechanism producing damage. Its general behavior is characterized by the formation of a water jet that penetrates through the bubble and the generation of a blast wave during the induced collapse. Both the jet and the blast wave are possible damaging mechanisms. However, the high-speed dynamics, the small spatio-temporal scales and the complicated physics involved in these processes make any theoretical and experimental approach a challenge.

Practical implications

Cavitation erosion is a major problem for hydraulic and marine applications. It is a limiting point for the conception and design of such components.

Originality/value

Such a comparison of multiphase models in the case of a strong shock-induced bubble collapse is clearly original. Usually models are tested separately leading to a large dispersion of results. Moreover, simulations of a three-dimensional bubble collapse are scarce in the literature using such fine grids.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 22 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 June 1958

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United…

Abstract

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.

Details

Aircraft Engineering and Aerospace Technology, vol. 30 no. 6
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 1 March 1997

M. Konstantinov

Presents the numerical investigations of interaction of several coaxial vortex rings in inviscid fluid. For the solution of non‐linear system of ordinary differential…

Abstract

Presents the numerical investigations of interaction of several coaxial vortex rings in inviscid fluid. For the solution of non‐linear system of ordinary differential equations chooses the method of extrapolation with variable step and order. Controls the accuracy of calculations by the conditions of conservation of the first integrals and also by the comparison of numerical results with the known analytical solutions. Discusses the problems of order and chaos, and presents examples of mixing of fluid particles by interaction of two and three vortex rings.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 7 no. 2/3
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 1 October 1963

I.M. Hall

THE development of undergraduate teaching in Aeronautical Engineering at Manchester University has followed a different pattern from that in most other Universities in…

Abstract

THE development of undergraduate teaching in Aeronautical Engineering at Manchester University has followed a different pattern from that in most other Universities in this country. Although Osborne Reynolds carried out his famous experiments in the Engineering Department at Manchester, the teaching of Aeronautical Engineering grew out of Mathematics rather than out of Engineering. For a large proportion of the past 80 years the Chair of Applied Mathematics has been held by men eminent in the field of Fluid Mechanics: Lamb, Goldstein and Lighthill must surely be names well‐known to every aeronautical engineer. It was due to the initiative of Professor S. Goldstein that a separate Department of Fluid Mechanics was set up in 1946 under the direction of Mr W. A. Mair. At first it was natural that the emphasis should be on experimental work to complement the theoretical work carried out in the Mathematics Department. Later, however, although close relations with the Mathematics Department were still maintained, the Mechanics of Fluids Department developed into a separate entity making both theoretical and experimental contributions to fundamental knowledge.

Details

Aircraft Engineering and Aerospace Technology, vol. 35 no. 10
Type: Research Article
ISSN: 0002-2667

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