Search results

1 – 10 of over 4000
To view the access options for this content please click here
Article
Publication date: 18 September 2019

Shiyu Feng, Chenchen Wang, Xiaotian Peng, Yan Yan, Yang Deng and Jun Chen

The purpose of this paper is to analyze the effects of the PRD geometric parameters, including the area and aspect ratio, on the discharge and force characteristics of…

Abstract

Purpose

The purpose of this paper is to analyze the effects of the PRD geometric parameters, including the area and aspect ratio, on the discharge and force characteristics of pressure relief process under various plenum compartment pressures and Mach numbers.

Design/methodology/approach

Under various plenum compartment pressures and Mach numbers, the effect of the area and aspect ratio on the discharge and force characteristics of the PRD are numerically investigated via a three-dimensional steady Reynolds-averaged Navier–Stokes equations solver based on structured grid technology.

Findings

When the aspect ratio remains constant, the discharge coefficient CD, thrust coefficient CT and moment coefficient CM are not affected by the PRD. When the area is constant, the aspect ratio dramatically impacts the discharge and force characteristics because the aspect ratio increases, the discharge coefficient CD of the PRD decreases, and the thrust coefficient CT and the moment coefficient CM both increase. When the aspect ratio is 2, the discharge coefficient CD decreases by 14.7 per cent, the thrust coefficient CT increases by 10-15 per cent, and the moment coefficient CM increases by 10-23 per cent compared with when the aspect ratio is 1.

Practical implications

This study provides detailed data and conclusions for nacelle PRD researchers and actual engineering applications.

Originality/value

On the basis of considering the influence of operating conditions on the discharge and force characteristics of the nacelle PRD, the impact of geometric parameters, including the area and aspect ratio on the discharge and force characteristics is comprehensively considered.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 2
Type: Research Article
ISSN: 1748-8842

Keywords

To view the access options for this content please click here
Article
Publication date: 27 May 2021

Wenchao Zhang

This paper aims to study the breakdown, oscillation and vanishing of the discharge channel and its influence on crater formation with simulation and experimental methods…

Abstract

Purpose

This paper aims to study the breakdown, oscillation and vanishing of the discharge channel and its influence on crater formation with simulation and experimental methods. The experiment results verified the effect of the oscillating characteristics of the discharge channel on the shape of the crater.

Design/methodology/approach

A mathematical model that considers the magnetohydrodynamics (MHD) and the discharge channel oscillation was established. The micro process of discharging based on magnetic-fluid coupling during electrical discharge machining (EDM) was simulated. The breakdown, oscillation and vanishing stage of the discharge channel were analyzed, and the crater after machining was obtained. Finally, a single-pulse discharge experiment during EDM was conducted to verify the simulation model.

Findings

During the breakdown of the discharge channel, the electrons move towards the center of the discharge channel. The electrons at the end diverge due to the action of water resistance, making the discharge channel appear wide at both ends and narrow in the middle, showing the pinch effect. Due to the mutual attraction of electrons and positive ions in the channel, the transverse oscillation of the discharge channel is shown on the micro level. Therefore, the position of the discharge point on the workpiece changes. The longitudinal oscillation in the discharge channel causes the molten pool on the workpiece to be ejected due to the changing pressure. The experimental results show that the shape of the crater is similar to that in the simulation, which verifies the correctness of the simulation results and also proves that the crater generated by the single pulse discharge is essentially the result of the interaction between transverse wave and longitudinal wave.

Originality/value

In this paper, the simulation of the discharge breakdown process in EDM was carried out, and a new mathematical model that considers the MHD and the discharge channel oscillation was established. Based on the MHD module, the discharge breakdown, oscillation and vanishing stages were simulated, and the velocity field and pressure field in the discharge area were obtained.

Details

Multidiscipline Modeling in Materials and Structures, vol. 17 no. 4
Type: Research Article
ISSN: 1573-6105

Keywords

To view the access options for this content please click here
Article
Publication date: 1 September 1998

Richard B. Parent and Simon Verdun‐Jones

This study examines the underlying reasons for the police use of deadly force and potential deadly force, in the Province of British Columbia, Canada, during the period…

Abstract

This study examines the underlying reasons for the police use of deadly force and potential deadly force, in the Province of British Columbia, Canada, during the period 1980‐94. Within this context, interactional violence and the phenomenon of victim‐precipitated homicide are examined in relation to the police use of deadly force. This study analyzes 58 separate documented incidents in which municipal and Royal Canadian Mounted Police officers, within the Province of British Columbia, have been confronted by a potentially lethal threat. In 27 of these incidents, the police responded by discharging their firearms and killing a total of 28 people. The remaining 31 cases that were examined reflect incidents in which the police responded with less‐lethal force. Through the examination of police investigations, verdict‐at‐coroner’s‐inquest reports, BC Police Commission data and interviews with police officers, this study reveals that, in roughly half of the cases examined (N = 28), the police reacted to a potentially lethal threat of victim‐precipitated homicide. These are incidents in which despondent individuals suffering from suicidal tendencies, mental illness, or extreme substance abuse, acted in a calculated and deliberate manner so as to force the police to use potential or deadly force. The study recommends that police personnel within the Province of British Columbia should be given further alternatives to the standard‐issue firearm, when responding to potentially lethal threats. Non‐lethal tools of compliance should be made readily available to the operational police officer with a view to providing alternatives to the traditional use of deadly force. In addition, the training of police personnel should emphasize non‐violent strategies in dealing with irrational individuals who are suicidal, mentally disordered and/or intoxicated.

Details

Policing: An International Journal of Police Strategies & Management, vol. 21 no. 3
Type: Research Article
ISSN: 1363-951X

Keywords

To view the access options for this content please click here
Article
Publication date: 2 October 2017

Qiang Ma and Zhenqian Chen

The paper aims to discuss the mass transfer of gas mixtures under the influence of electrohydrodynamic (EHD) flow induced by direct current (DC) corona discharge of…

Abstract

Purpose

The paper aims to discuss the mass transfer of gas mixtures under the influence of electrohydrodynamic (EHD) flow induced by direct current (DC) corona discharge of wire-to-plane electrode, using a coupled numerical model.

Design/methodology/approach

A coupled numerical method is developed in this paper. Lattice Boltzmann model of binary gas mixtures coupled with the Coulomb force as an external force is introduced to predict the gas flow and species transport affected by EHD flow. Meanwhile, the distributions of electric field and space charge density during DC corona discharge are obtained using the finite difference method and the method of characteristics.

Findings

The numerical results of mass transfer effected by EHD flow reveal that the high electric field intensity is observed near the surface of corona wire, which causes the higher Coulomb force to form the EHD flow pattern of anticlockwise vortex. The EHD vortex flow plays a considerable role in the mass transport enhancement of gas species emit from the plane electrode, and the significant difference of the local Sherwood number is presented along the direction parallel to plane electrode. In addition, the enhance effectiveness with the different applied voltage is assessed, and the influencing mechanism of enhancement is investigated in this work.

Originality/value

The proposed numerical model will be useful in the study of mass transfer and fluid flow effected by EHD.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 10
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 6 August 2019

Mohammad Haji Mohammadi and Joshua R. Brinkerhoff

Turbomachinery, including pumps, are mainly designed to extract/produce energy from/to the flow. A major challenge in the numerical simulation of turbomachinery is the…

Abstract

Purpose

Turbomachinery, including pumps, are mainly designed to extract/produce energy from/to the flow. A major challenge in the numerical simulation of turbomachinery is the inlet flow rate, which is routinely treated as a known boundary condition for simulation purposes but is properly a dependent output of the solution. As a consequence, the results from numerical simulations may be erroneous due to the incorrect specification of the discharge flow rate. Moreover, the transient behavior of the pumps in their initial states of startup and final states of shutoff phases has not been studied numerically. This paper aims to develop a coupled procedure for calculating the transient inlet flow rate as a part of the solution via application of the control volume method for linear momentum. Large eddy simulation of a four-blade axial hydraulic pump is carried out to calculate the forces at every time step. The sharp interface immersed boundary method is used to resolve the flow around the complex geometry of the propeller, stator and the pipe casing. The effect of the spurious pressure fluctuations, inherent in the sharp interface immersed boundary method, is damped by local time-averaging of the forces. The developed code is validated by comparing the steady-state volumetric flow rate with the experimental data provided by the pump manufacturer. The instantaneous and time-averaged flow fields are also studied to reveal the flow pattern and turbulence characteristics in the pump flow field.

Design/methodology/approach

The authors use control volume analysis for linear momentum to simulate the discharge rate as part of the solution in a large eddy simulation of an axial hydraulic pump. The linear momentum balance equation is used to update the inlet flow rate. The sharp interface immersed boundary method with dynamic Smagorinsky sub-grid stress model and a proper wall model is used.

Findings

The steady-state volumetric flow rate has been computed and validated by comparing to the flow rate specified by the manufacturer at the simulation conditions, which shows a promising result. The instantaneous and time averaged flow fields are also studied to reveal the flow pattern and turbulence characteristics in the pump flow field.

Originality/value

An approach is proposed for computing the volumetric flow rate as a coupled part of the flow solution, enabling the simulation of turbomachinery at all phases, including the startup/shutdown phase. To the best of the authors’ knowledge, this is the first large eddy simulation of a hydraulic pump to calculate the transient inlet flow rate as a part of the solution rather than specifying it as a fixed boundary condition. The method serves as a numerical framework for simulating problems incorporating complex shapes with moving/stationary parts at all regimes including the transient start-up and shut-down phases.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 2 August 2013

Imran Halimi Bin Ibrahim and Martin Skote

For the past decade, plasma actuators have been identified as a subset in the realm of active flow control devices. As research into plasma actuators continues to mature…

Abstract

Purpose

For the past decade, plasma actuators have been identified as a subset in the realm of active flow control devices. As research into plasma actuators continues to mature, computational modelling is needed to complement the investigation of the actuators. This paper seeks to address these issues.

Design/methodology/approach

In this study, the Suzen‐Huang model is chosen because of its ability to simulate both the charge density and Lorentz body force. Its advantages and limitations have been identified with a parametric study of two constants used in the modelling: the Debye length (λD) and the maximum charge density value (ρc* ). By varying the two scalars, the effects of charge density, body force and induced velocity are examined.

Findings

The results show that the non‐dimensionalised body force (Fb*) is nonlinearly dependent on Debye length. However, a linear variation of Fb* is observed with increasing values of maximum charge density. The optimized form of the Suzen‐Huang model shows better agreement in the horizontal velocity profile but still points to inaccuracy when compared to vertical velocity profile.

Originality/value

The results indicate that the body force still has to be modelled more extensively above the encapsulated electrode, so that the horizontal and vertical components of induced velocities are accurately obtained.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 23 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 8 March 2011

Yong Lu, Wei Zhang, Yuan‐yang Zhao, Zhi‐zhong Wang and Peng‐cheng Shu

The balanced vane pump is a common transmission component in hydraulic systems. Since the physicochemical properties of water and seawater are different from that of…

Abstract

Purpose

The balanced vane pump is a common transmission component in hydraulic systems. Since the physicochemical properties of water and seawater are different from that of mineral oil, some problems can occur, for instance, poor lubrication, more leakage, and more corrosion. The paper aims to demonstrate the technical feasibility for the water hydraulic vane pump.

Design/methodology/approach

The material combinations were selected based on related research in literature. The volumetric efficiency and suction performance were measured in the current experiment. The relations between gap clearances and leakage flow, the contact and the friction forces between a vane tip and a cam contour were simulated based on mathematic models.

Findings

The soft‐hard material combinations in the prototype pump show preferable friction characteristics during tests. The axial clearances are the main channels of leakage flow. Pin type vane pump can reduce the contact force of the vane tip.

Originality/value

This paper outlines some key problems of the water hydraulic vane pump, such as the friction pair material,the structure, and the contact force of the vane tip by means of testing the basic performance of pump and mathematic model.

Details

Industrial Lubrication and Tribology, vol. 63 no. 2
Type: Research Article
ISSN: 0036-8792

Keywords

To view the access options for this content please click here
Article
Publication date: 1 March 1991

S. ABDEL‐SATTAR

In this paper, the electrical parameters of the duct electrostatic precipitators with bundle wires, as discharge electrodes, are calculated and reported. Variation of…

Abstract

In this paper, the electrical parameters of the duct electrostatic precipitators with bundle wires, as discharge electrodes, are calculated and reported. Variation of mobility for both ions and particles in the space surrounding the energized subwires is taken into consideration. The method used is based on numerically solving the main set of equations, defining the ionized field surrounding the subwires of the bundle wire‐duct electrostatic precipitators (BWDEP) with the presence of dust particles. This method predicts the electrical performance in the BWDEP irrespective of the number of subwires per bundle. The corona onset voltage around the periphery of each subwire of the bundled discharge electrodes of the duct electrostatic precipitators is determined. It changes from point to point at the subwire surface. The effects of different numbers of subwires per bundled electrode, as well as the subwires arrangement, on the electrical performance of the BWDEP are also reported and discussed in this paper. The present findings are correlated to the physics of the electrical corona discharge.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 10 no. 3
Type: Research Article
ISSN: 0332-1649

To view the access options for this content please click here
Article
Publication date: 29 April 2021

Günsu Merin Abbas and Ipek Gursel Dino

Biocontaminants represent higher risks to occupants' health in shared spaces. Natural ventilation is an effective strategy against indoor air biocontamination. However…

Abstract

Purpose

Biocontaminants represent higher risks to occupants' health in shared spaces. Natural ventilation is an effective strategy against indoor air biocontamination. However, the relationship between natural ventilation and indoor air contamination requires an in-depth investigation of the behavior of airborne infectious diseases, particularly concerning the contaminant's viral and aerodynamic characteristics. This research investigates the effectiveness of natural ventilation in preventing infection risks for coronavirus disease (COVID-19) through indoor air contamination of a free-running, naturally-ventilated room (where no space conditioning is used) that contains a person having COVID-19 through building-related parameters.

Design/methodology/approach

This research adopts a case study strategy involving a simulation-based approach. A simulation pipeline is implemented through a number of design scenarios for an open office. The simulation pipeline performs integrated contamination analysis, coupling a parametric 3D design environment, computational fluid dynamics (CFD) and energy simulations. The results of the implemented pipeline for COVID-19 are evaluated for building and environment-related parameters. Study metrics are identified as indoor air contamination levels, discharge period and the time of infection.

Findings

According to the simulation results, higher indoor air temperatures help to reduce the infection risk. Free-running spring and fall seasons can pose higher infection risk as compared to summer. Higher opening-to-wall ratios have higher potential to reduce infection risk. Adjacent window configuration has an advantage over opposite window configuration. As a design strategy, increasing opening-to-wall ratio has a higher impact on reducing the infection risk as compared to changing the opening configuration from opposite to adjacent. However, each building setup is a unique case that requires a systematic investigation to reliably understand the complex airflow and contaminant dispersion behavior. Metrics, strategies and actions to minimize indoor contamination risks should be addressed in future building standards. The simulation pipeline developed in this study has the potential to support decision-making during the adaptation of existing buildings to pandemic conditions and the design of new buildings.

Originality/value

The addressed need of investigation is especially crucial for the COVID-19 that is contagious and hazardous in shared indoors due to its aerodynamic behavior, faster transmission rates and high viral replicability. This research contributes to the current literature by presenting the simulation-based results for COVID-19 as investigated through building-related and environment-related parameters against contaminant concentration levels, the discharge period and the time of infection. Accordingly, this research presents results to provide a basis for a broader understanding of the correlation between the built environment and the aerodynamic behavior of COVID-19.

Details

Engineering, Construction and Architectural Management, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 0969-9988

Keywords

To view the access options for this content please click here
Article
Publication date: 1 April 1972

J.D. IBBOTT BSc CEng MIEE

AFTER BRIEFLY considering the surface areas of aircraft for which lightning strikes are a major factor in the selection of constructional materials, a review is made of…

Abstract

AFTER BRIEFLY considering the surface areas of aircraft for which lightning strikes are a major factor in the selection of constructional materials, a review is made of published information concerning the effects of lightning on these various materials. The materials are considered under three headings: metallic, non‐conducting (e.g. glass‐fibre‐reinforced‐plastics) and semi‐conducting (e.g. carbon‐fibre‐reinforced plastics). Simulated lightning current tests are the main source of information and the review is primarily concerned with the results of such tests. To aid assessment of the relevance of the test currents that have been used, an outline of the current characteristics of lightning discharges is also given.

Details

Aircraft Engineering and Aerospace Technology, vol. 44 no. 4
Type: Research Article
ISSN: 0002-2667

1 – 10 of over 4000