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Article
Publication date: 29 June 2020

Chaoyue Wang, Fujun Wang, Changliang Ye, Benhong Wang and Zhichao Zou

Tip leakage vortex flow (TLV) is a common flow phenomenon in the axial-flow hydraulic machinery. High-efficiency simulation of TLV is still not an easy task because of the…

Abstract

Purpose

Tip leakage vortex flow (TLV) is a common flow phenomenon in the axial-flow hydraulic machinery. High-efficiency simulation of TLV is still not an easy task because of the complex turbulent vortex-cavitation interactions. As an important basis of CFD, turbulence model directly affects the efficient computation of TLV. The purpose of this paper is to evaluate the newly developed MST turbulence model in predicting the TLV flows.

Design/methodology/approach

By using the MST turbulence model and the ZGB cavitation model, numerical simulations of the TLV generated by a NACA0009 hydrofoil were performed under the cavitation-free and cavitation conditions, and the results were compared with the available experimental data.

Findings

The important features of TLV are well captured by the MST-based simulation scheme, and the problem of under-predicting the cavitating TLV tube is well solved. Turbulent viscosity is reasonably adjusted in the TLV core regions, and the LES-like mode is activated, which is beneficial to obtain more turbulent information on the same URANS grids. The requirements of grid size and time step of the MST model are much lower than that of the LES method, thereby weighing a good balance between the simulation accuracy and computation cost.

Originality/value

The MST turbulence model is suitable for the high-efficiency simulation of the TLV flows, which can lay a good foundation for efficient engineering computations of the cavitating TLV in the axial-flow hydraulic machinery.

Details

Engineering Computations, vol. 38 no. 1
Type: Research Article
ISSN: 0264-4401

Keywords

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Article
Publication date: 14 July 2020

Ahmad Fikri Mustaffa and Vasudevan Kanjirakkad

This paper aims to understand the aerodynamic blockage related to near casing flow in a transonic axial compressor using numerical simulations and to design an optimum…

Abstract

Purpose

This paper aims to understand the aerodynamic blockage related to near casing flow in a transonic axial compressor using numerical simulations and to design an optimum casing groove for stall margin improvement using a surrogate optimisation technique.

Design/methodology/approach

A blockage parameter (Ψ) is introduced to quantify blockage across the blade domain. A surrogate optimisation technique is then used to find the optimum casing groove design that minimises blockage at an axial location where the blockage is maximum at near stall conditions.

Findings

An optimised casing groove that improves the stall margin by about 1% can be found through optimisation of the blockage parameter (Ψ).

Originality/value

Optimising for stall margin is rather lengthy and computationally expensive, as the stall margin of a compressor will only be known once a complete compressor map is constructed. This study shows that the cost of the optimisation can be reduced by using a suitably defined blockage parameter as the optimising parameter.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

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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

Keywords

Content available
Article
Publication date: 9 November 2018

Wantanee Phanprasit, Kanchanok Songpek, Vorakamol Boonyayothin and Dusit Sujirarat

The purpose of this paper is to explore inhalation levels and dermal exposure to toluene among printing workers who wore no personal protective equipment; it is conducted…

Abstract

Purpose

The purpose of this paper is to explore inhalation levels and dermal exposure to toluene among printing workers who wore no personal protective equipment; it is conducted in a plastic bag factory. Using a charcoal cloth pad (CCP) as a dermal sampler to assess skin permeation of liquid toluene is also investigated.

Design/methodology/approach

In total, 27 stationary air samples as well as urine and dermal samples were collected over 9 days from 11 printing workers. Six pieces of CCP were wrapped on each of the workers’ fingers for the dermal sample collection. Air samples were collected and analyzed according to NIOSH No. 1501, and 65 post-shift urine samples were collected and analyzed using gas chromatography equipped with headspace sampler (GC-HS/FID). Multiple linear regression was employed to analyze the association between the studied variables.

Findings

The mean (SD) urinary toluene (UTol) level was 13.42 (9.72) ug/L. Toluene on the CCP (TolCCP) was a meaningful predictor for UTol (p-value=0.027) with r and r2 values of 0.441 and 0.195, respectively. The r and r2 of the model using the toluene time-weighted average concentrations in air were 0.739 and 0.546, respectively. The absorbed dose of toluene determined from the TolCCP ranged from 1.05 to 91.94 mg, accounting for 12.3 percent of the threshold limit value (TLV).

Originality/value

Dermal exposure was insignificant when workers wore respirators, but when not, dermal absorption could contribute to the overall uptake and exposure above the TLV. Appropriate gloves should be assigned to the workers to reduce dermal exposure to toluene.

Details

Journal of Health Research, vol. 33 no. 1
Type: Research Article
ISSN: 2586-940X

Keywords

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Article
Publication date: 30 August 2019

Fujuan Tong, Wenxuan Gou, Lei Li, Zhufeng Yue, Wenjing Gao and Honglin Li

In order to improve the engine reliability and efficiency, an effective way is to reform the turbine blade tip conformation. The paper aims to discuss this issue.

Abstract

Purpose

In order to improve the engine reliability and efficiency, an effective way is to reform the turbine blade tip conformation. The paper aims to discuss this issue.

Design/methodology/approach

The present research provides several novel tip-shaping structures, which are considered to control the blade tip loss. Four different tip geometries have been studied: flat tip, squealer tip, flat tip with streamwise ribs and squealer tip with streamwise ribs. The tip heat transfer and leakage flow are both analyzed in detail, for example the tip heat transfer coefficient, tip flow and local pressure distributions.

Findings

The results show that the squealer seal and streamwise rib can reduce the tip heat transfer and leakage loss, especially for the squealer tip with streamwise ribs. The tip and near-tip flow patterns at the different locations of axial chord reflect that both the squealer seal and streamwise rib structure can control the tip leakage flow loss. In addition, the analysis of the aerodynamic parameters (the static pressure and turbine efficiency) also indicates that the squealer tip with streamwise ribs obtains the highest adiabatic efficiency with an increase of 2.34 percent, compared with that of the flat tip case.

Originality/value

The analysis of aerothermal and dynamic performance can provide a reference for the blade tip design and treatment.

Details

Multidiscipline Modeling in Materials and Structures, vol. 15 no. 6
Type: Research Article
ISSN: 1573-6105

Keywords

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Article
Publication date: 1 April 1988

G. Messner

Wherever solvents and solvent containing systems are employed, protection for people and the environment is a vital factor in the way that they are used. The paper…

Abstract

Wherever solvents and solvent containing systems are employed, protection for people and the environment is a vital factor in the way that they are used. The paper addresses the following: Minimum contamination of the environment (air and water) by solvent emission; adherence to existing occupational safety laws: process technology and equipment that ensure high safety levels, and non polluting waste disposal.

Details

Circuit World, vol. 15 no. 1
Type: Research Article
ISSN: 0305-6120

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Article
Publication date: 1 April 1975

W. MacLeod Ross

Many potentially hazardous materials and processes are employed in the manufacture of printed circuits and printed circuit assemblies. This article draws attention to…

Abstract

Many potentially hazardous materials and processes are employed in the manufacture of printed circuits and printed circuit assemblies. This article draws attention to these and lists the salient properties of those most commonly employed. Methods of assisting in the assurance of the safety of personnel handling and processing these materials are suggested. It is stressed that it is important always to know exactly what is being handled and how it is being modified by process operations. Finally, suggestions are made with regard to the availability of information and assistance and the need for communication with, and education of, all personnel concerned.

Details

Circuit World, vol. 2 no. 1
Type: Research Article
ISSN: 0305-6120

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Article
Publication date: 13 September 2011

Robert Bogue

The purpose of this paper is to review recent developments in the sensing of electromagnetic radiation (EMR) with wavelengths longer than those of visible light.

Abstract

Purpose

The purpose of this paper is to review recent developments in the sensing of electromagnetic radiation (EMR) with wavelengths longer than those of visible light.

Design/methodology/approach

Following a short introduction, this paper discusses recent research into the sensing of infra‐red (IR), terahertz (THz) and microwave radiation.

Findings

It is shown that novel sensors are being developed for all of these classes of EMR. Improved IR sensors are attracting strong interest from the military, novel THz sensor developments reflect the growing uses of this radiation and research into cosmology and astronomy are driving the development of highly sensitive microwave sensors.

Originality/value

The paper provides a technical review of recent research into sensing IR, THz and microwave radiations.

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Article
Publication date: 1 August 1992

Mark Hinnebusch

I promised that this month I would demonstrate a Z39.50 connection by emulating the two systems, showing the messages the protocol data units (PDUs) generated by each…

Abstract

I promised that this month I would demonstrate a Z39.50 connection by emulating the two systems, showing the messages the protocol data units (PDUs) generated by each system. Before doing this, however, I need to digress to discuss syntaxes. In order for two systems to communicate, they not only need to agree on what will be sent but also on how this information will be represented. OSI protocols in general, and Z39.50 in particular, specify information representation by defining a “transfer syntax.” A transfer syntax consists of a humanly representable definition of the information, called the “abstract syntax,” and specification of the rules used to encode the abstract syntax into a format manageable by machines.

Details

Academic and Library Computing, vol. 9 no. 8
Type: Research Article
ISSN: 1055-4769

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Article
Publication date: 1 April 1989

K. Johnson and T.J. Crawford

The Materials and Processes Research Laboratory of the Electronics Manufacturing Productivity Facility (EMPF) is undertaking a research project to examine the use of…

Abstract

The Materials and Processes Research Laboratory of the Electronics Manufacturing Productivity Facility (EMPF) is undertaking a research project to examine the use of solvents in a vapour decreasing process. Fourteen solvents are included in this project. During the research, it was found that the concentration of the denaturant Methanol (MEOH) in the trichlorotrifluoroethane/ethanol (TCF/ethanol) mixture in the vapour degreaser boil sump was being depleted. The fresh material had a concentration of 0 · 35 percent MEOH by volume but the test data showed that this concentration dropped to levels between 0·19 and 0·11 percent MEOH. MEOH depletion in trichlorotrifluoroethane/methanol (TCE/methanol) azeotrope was also detected. The alcohol depletion that was discovered is a concern because when one component of an azeotrope breaks down, the entire azeotrope is affected and the constant boiling feature is no longer present. MEOH separation may also be a flammability hazard and may decrease the Threshold Limit Value (TLV) of the solvent because of MEOH toxicity. It was determined that the MEOH depletion was caused by the molecular sieve or desiccant adsorbing the alcohol. Recommendations are offered to minimise the flammability hazard associated with a MEOH‐adsorbing molecular sieve.

Details

Circuit World, vol. 16 no. 1
Type: Research Article
ISSN: 0305-6120

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