Xianbei Huang, Yaojun Li, Zhuqing Liu and Wei Yang
The purpose of this paper is to obtain a better understanding of the rotor–stator interaction in the vaneless region of a centrifugal pump.
Abstract
Purpose
The purpose of this paper is to obtain a better understanding of the rotor–stator interaction in the vaneless region of a centrifugal pump.
Design/methodology/approach
A third-order sub-grid scale (SGS) model containing the rotation rate tensor named the dynamic cubic non-linear model (DCNM) is used for simulating the flow field in a centrifugal pump with a vaned diffuser. The pressure coefficient and velocity distributions are compared with the experimental data. Focusing on the vaneless region, the pressure pulsation, Reynolds stress pulsation and Reynolds stress transport equation are analyzed.
Findings
The comparison of the calculation results with the experimental data indicates that the DCNM can accurately capture the distributions of pressure and velocity in the vaneless region. Based on the instantaneous pressure signals, the pressure pulsation is analyzed to show that in the vaneless region, the dominant frequency near the impeller is twice the blade passing frequency, whereas it is equal to the blade passing frequency near the diffuser. Further exploration of the Reynolds stress pulsation shows the correlation between the two variables. Additionally, the extreme low frequency of Reynolds stress near the diffuser is found to be related to the rotation instability. To explore the turbulence characteristics in the vaneless region, the Reynolds stress transportation equation is studied. In the vaneless region, the rotation term of the Reynolds stress transport equation is negligible compared to the production term, although the rotation instability is obvious near the diffuser. The production of the Reynolds stress plays the role of redistributing the energy from the uu component to the vv component, except for the region near the impeller outlet.
Originality/value
The third-order SGS model DCNM has proved to be promising in simulating the rotor–stator interaction. The analysis of the rotation instability and the Reynolds stress transport equation shed light on the further understanding of the rotor–stator interaction.
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Kaiwen Pang, Xianbei Huang, Zhuqing Liu, Yaojun Li, Wei Yang and Jiaxing Lu
This study aims to research the prediction performance of the bifurcation approach with different base models in different kinds of turbulent flows with rotation and curvature.
Abstract
Purpose
This study aims to research the prediction performance of the bifurcation approach with different base models in different kinds of turbulent flows with rotation and curvature.
Design/methodology/approach
The k−ω and Shear-Stress Transport (SST) k−ω models are modified by using the complete eddy viscosity coefficient expression, and the latter is modified by using two sets of model coefficients. The two bifurcation models were tested in three cases: rotating channel flow with system rotation, Taylor–Couette flow with wall rotation and curvature effect and swirling flow through an abrupt axisymmetric expansion with inlet swirling flow.
Findings
In these flows, the bifurcation approach can significantly improve the prediction performance of the base model in the fluctuation velocity. The deviation of the BSkO model is slightly superior to the BkO model by about 2% in the Taylor–Couette flow. The prediction effect of the root-mean-square (RMS) velocity of the BSkO model increases by about 4–5% as the number of grids increases about 2.37 times, and the best is the Large Eddy Simulation (LES) grid used. Finally, compared with the SST k−ω model, the average iteration time of the SST with curvature correction (SST-CC), bifurcation k−ω (BkO) and bifurcation SST k−ω (BSkO) models increased by 27.7%, 86.9% and 62.3%, respectively.
Originality/value
This study is helpful to understand further the application of the bifurcation method in the turbulence model.
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Kaiwen Pang, Yaojun Li, Wei Yang and Zhuqing Liu
This study aims to develop and validate a new cavitation model that considers thermodynamic effects for high-temperature water flows.
Abstract
Purpose
This study aims to develop and validate a new cavitation model that considers thermodynamic effects for high-temperature water flows.
Design/methodology/approach
The Rayleigh–Plesset equation and “B-factor” method proposed by Franc are used to construct a new cavitation model called “thermodynamic Zwarte–Gerbere–Belamri” (TZGB) by introducing the thermodynamic effects into the original ZGB model. Furthermore, the viscous term of the Rayleigh–Plesset equation is considered in the TZGB model, and the model coefficients are formulated as a function of temperature. Cavitating flows around the NACA0015 hydrofoil under different water temperatures (25°C, 50°C and 70°C) at the angle of attack of 5° are calculated.
Findings
Results of the investigated temperatures show good agreement with the available experimental data. Given that the thermodynamic and viscosity effects are included in the TZGB model and the model coefficients are treated as a function of temperature, the TZGB model shows better performance in predicting the pressure coefficient distribution and length of cavity than the original ZGB cavitation model and other models do. The TZGB model aims to determine the thermodynamic and viscosity effects and perform better than the other models in predicting the mass transfer rate, particularly in high-temperature water.
Originality/value
The TZGB model shows potential in predicting the cavitating flows at high temperature and the computational cost of this model is similar to that of the original ZGB model.
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Xianbei Huang, Baoyun Qiu, Qiang Guo, Zhuqing Liu, Wei Yang and Yaojun Li
Construct a new sub-grid scale (SGS) model which can improve the efficiency and maintain comparative accuracy comparing to the existing dynamic cubic non-linear SGS model (DCNM).
Abstract
Purpose
Construct a new sub-grid scale (SGS) model which can improve the efficiency and maintain comparative accuracy comparing to the existing dynamic cubic non-linear SGS model (DCNM).
Design/methodology/approach
The polynomial constitutive relation between the SGS stress tensor and both strain and rotation rate is selected as a basement. Simplification is achieved by eliminating the solid-body rotation term and adopting the assumption proposed by Kosovic. A dynamic procedure is applied to calculate three model coefficients in the new model. The new model (named dynamic simplified Lund model) and DCNM are applied to the rotating channel flow and the internal flow in a centrifugal pump impeller to examine the performance.
Findings
The new model is as accurate as DCNM but decreases 25 per cent computational resources. The ability of capturing rotation effect and reflecting backscatter is verified through cases. In addition, good numerical stability is shown during the calculation.
Research limitations/implications
More benchmark and engineering cases should be used to get further confidence on the new model.
Practical implications
The new model is promising in industrial application with the advantage of both accuracy and efficiency. For the flow with large-scale separation or more complicate phenomenon, the model is thought to give accurate flow structure.
Originality/value
A new non-linear SGS model is proposed in this paper. The accuracy, numerical stability and efficiency are validated for this model. Therefore, it is promising in the prediction of the flow structure in centrifugal pumps.
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This paper seeks to investigate ethnic disadvantages in the UK labour market in the last three decades. Design/methodology/approach – Drawing on data from the most authoritative…
Abstract
Purpose
This paper seeks to investigate ethnic disadvantages in the UK labour market in the last three decades. Design/methodology/approach – Drawing on data from the most authoritative government surveys, the gross and net differences in employment status and class position between minority ethnic and White British men covering 34 years (1972‐2005) are analysed.
Findings
White British and White Other men were generally advantaged in employment and in access to professional and managerial (salariat) jobs. White Irish men were making steady progress, and have now caught up with the White British. Black men were much more likely to be unemployed in recession years but progress is discernible with Black Caribbeans approaching, and Black Africans frequently outperforming, the White British in gaining access to the salariat. Indian and Chinese men were behind the White British in employment but little different in access to the salariat. Pakistani/Bangladeshi men were most disadvantaged in both respects.
Originality/value
This is the most systematic research in this area so far, using the most authoritative data and covering such a long period.
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We analyse the labour market position of the second-generation minority ethnic groups in Britain and the United States in 1990 and 2000 on the basis of micro-data from the two…
Abstract
We analyse the labour market position of the second-generation minority ethnic groups in Britain and the United States in 1990 and 2000 on the basis of micro-data from the two most recent censuses of the population. We find that they were making progress, although some groups were still facing considerable disadvantages. The second-generation men were doing better in the United States than in Britain at both time points but the gaps were being narrowed. The second-generation women in Britain lagged behind their American counterparts in the first period, but they were doing equally well in the two countries in 2001. The overall pattern is one of small but notable progress and shows somewhat greater support for the revised straight-line theory than for the segmented assimilation theory.
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Yang Gao, Yangyang Li and Yaojun Wang
This paper aims to explore the interaction between investor attention and green security markets, including green bonds and stocks.
Abstract
Purpose
This paper aims to explore the interaction between investor attention and green security markets, including green bonds and stocks.
Design/methodology/approach
This study takes the Baidu index of “green finance” as the proxy for investor attention and constructs several generalized prediction error variance decomposition models to investigate the interdependence. It further analyzes the dynamic interaction between investor attention and the return and volatility of green security markets using the rolling time window.
Findings
The empirical analysis and robustness test results reveal that the spillovers between investor attention and the return and volatility of the green bond market are relatively stable. In contrast, the spillover level between investor attention and the green stock market displays significant time-varying and asymmetric effects. Moreover, the volatility spillover between investor attention and green securities is vulnerable to major financial events, while the return spillover is extremely sensitive to market performance.
Originality/value
The conclusion further expands the practical application and theoretical framework of behavioral finance in green finance and provides a new reference for investors and regulators. Besides, this study also lays a theoretical basis for investors to focus on the practical application of volatility prediction and risk management in green securities.