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Article
Publication date: 8 July 2019

Massoud Tatar, Mojtaba Tahani and Mehran Masdari

In this paper, the applicability of shear stress transport k-ω model along with the intermittency concept has been investigated over pitching airfoils to capture the…

Abstract

Purpose

In this paper, the applicability of shear stress transport k-ω model along with the intermittency concept has been investigated over pitching airfoils to capture the laminar separation bubble (LSB) position and the boundary layer transition movement. The effect of reduced frequency of oscillations on boundary layer response is also examined.

Design/methodology/approach

A two-dimensional computational fluid dynamic code was developed to compute the effects of unsteadiness on LSB formation, transition point movement, pressure distribution and lift force over an oscillating airfoil using transport equation of intermittency accompanied by the k-ω model.

Findings

The results indicate that increasing the angle of attack over the stationary airfoil causes the LSB size to shorten, leading to a rise in wall shear stress and pressure suction peak. In unsteady cases, both three- and four-equation models are capable of capturing the experimentally measured transition point well. The transition is delayed for an unsteady boundary layer in comparison with that for a static airfoil at the same angle of attack. Increasing the unsteadiness of flow, i.e. reduced frequency, moves the transition point toward the trailing edge of the airfoil. This increment also results in lower static pressure suction peak and hence lower lift produced by the airfoil. It was also found that the fully turbulent k-ω shear–stress transport (SST) model cannot capture the so-called figure-of-eight region in lift coefficient and the employment of intermittency transport equation is essential.

Practical implications

Boundary layer transition and unsteady flow characteristics owing to airfoil motion are both important for many engineering applications including micro air vehicles as well as helicopter blade, wind turbine and aircraft maneuvers. In this paper, the accuracy of transition modeling based on intermittency transport concept and the response of boundary layer to unsteadiness are investigated.

Originality/value

As a conclusion, the contribution of this paper is to assess the ability of intermittency transport models to predict LSB and transition point movements, static pressure distribution and aerodynamic lift variations and boundary layer flow pattern over dynamic pitching airfoils with regard to oscillation frequency effects for engineering problems.

Details

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

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Article
Publication date: 23 January 2019

Konrad Nering and Kazimierz Rup

For internal flows with small values of the Reynolds number, there is often at a considerable distance from the pipe inlet cross-section a change of the flow form from…

Abstract

Purpose

For internal flows with small values of the Reynolds number, there is often at a considerable distance from the pipe inlet cross-section a change of the flow form from laminar to turbulent. To describe this phenomenon of laminar-turbulent transition in the pipe, also parallel-plate channel flow, a modified algebraic intermittency model was used. The original model for bypass transition developed by S. Kubacki and E. Dick was designed for simulating bypass transition in turbomachinery.

Design/methodology/approach

A modification of mentioned model was proposed. Modified model is suitable for simulating internal flows in pipes and parallel-plate channels. Implementation of the modified model was made using the OpenFOAM framework. Values of several constants of the original model were modified.

Findings

For selected Reynolds numbers and turbulence intensities (Tu), localization of laminar breakdown and fully turbulent flow was presented. Results obtained in this work were compared with corresponding experimental results available in the literature. It is particularly worth noting that asymptotic values of wall shear stress in flow channels and asymptotic values of axis velocity obtained during simulations are similar to related experimental and theoretical results.

Originality/value

The modified model allows precision numerical simulation in the area of transitional flow between laminar, intermittent and turbulent flows in pipes and parallel-plate channels. Proposed modified algebraic intermittency model presented in this work is described by a set of two additional partial differential equations corresponding with k-omega turbulence model presented by Wilcox (Wilcox, 2006).

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 4
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 4 January 2013

Ivan Langella, Carlo Scalo, Giuseppe De Felice and Carlo Meola

The purpose of this paper is to discuss some fundamental aspects regarding the anomalies in the passive scalar field advected by forced homogenous and isotropic…

Abstract

Purpose

The purpose of this paper is to discuss some fundamental aspects regarding the anomalies in the passive scalar field advected by forced homogenous and isotropic turbulence, by inspection of the analytical properties of the governing equations and with the aid of direct numerical simulation (DNS) data.

Design/methodology/approach

Results from a pseudo‐spectral DNS of a unitary‐Schmidt‐ number passive scalar advected by a low Reynolds number flow field, Reλ=50 and 70 (based on the Taylor microscale λ) allow for a preliminary assessment of the developed numerical model.

Findings

Manipulation of the governing equations for the scalar field (which are monotonic) reveals that the unboundedness of the scalar gradient magnitude is not ruled out by the mathematical properties of the correspondent conservation equation. Classic intermittency effects in the passive scalar field have been reproduced, such as non‐Gaussian behavior of the passive scalar statistics, loss of local isotropy, and multi‐fractal scaling of scalar structure functions. Moreover, Taylor and Richardson theories are, surprisingly, not confirmed only in the dissipation range (small‐scales anomalies).

Originality/value

The authors suggest that the origin of intermittency (qualitatively pictured here as violent burst in spatial gradient quantities) should be sought in the loss of monotonicity of the evolution equation of the scalar gradient.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 23 no. 1
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 5 September 2016

George Zografakis and George Barakos

This paper aims to explore the potential of transition prediction methods for modelling transitional shock wave/boundary layer interactions. The study is fuelled by the…

Abstract

Purpose

This paper aims to explore the potential of transition prediction methods for modelling transitional shock wave/boundary layer interactions. The study is fuelled by the strong interest of researchers and airframe manufacturers in reducing the drag of vehicles flying at transonic speeds. The principle of drag reduction via flow laminarity is valid, provided there is no need for the flow to sustain large pressure gradients or shocks. This is true, as laminar boundary layers are less resistant to flow separation.

Design/methodology/approach

It is, therefore, worthwhile to assess the performance of CFD methods in modelling laminar boundary layers that can be tripped to turbulent just before an interaction with a shock. In this work, the CFD solver of Liverpool University is used. The method is strongly implicit, and, for this reason, the implementation of intermittency-based models requires special attention. The Navier–Stokes equations, the transport equations of the kinetic energy of turbulence and the turbulent frequency are inverted at the same time as the transport equations for the flow intermittency and the momentum thickness Reynolds number.

Findings

The result is stable and robust convergence even for complex three-dimensional flow cases. The method is demonstrated for the flow around the V2C section of the TFAST EU, F7 project. The results suggest that the intermittency-based model captures the fundamental physics of the interaction, but verification and validation are needed to ensure that accurate results can be obtained. For this reason, comparisons with the TFAST experiments is put forward as a means of establishing confidence in the transition prediction tools used for shock/boundary layer interaction simulation.

Research limitations/implications

At the moment, experimental data for transonic transitional buffet are not yet available, although this will change in the near future.

Practical implications

The required CPU time is neither insignificant not prohibitive for routine computations.

Social implications

Reducing aircraft drag without compromising on stall characteristics will result in lower fuel consumption and contribute to a greener and more economic flight for passengers.

Originality/value

To the authors’ knowledge, this is the first time that transitional buffet has been addressed.

Details

Aircraft Engineering and Aerospace Technology, vol. 88 no. 5
Type: Research Article
ISSN: 1748-8842

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Article
Publication date: 10 July 2017

Lingcheng Kong, Zhong Li, Ling Liang and Jiaping Xie

When the power generator faces uncertain and independent electricity spot price and renewable energy source supply, two different conditions need to be considered: the…

Abstract

Purpose

When the power generator faces uncertain and independent electricity spot price and renewable energy source supply, two different conditions need to be considered: the distributions of renewable energy source electricity and electricity spot price are independent or dependent. The purpose of this paper is to explore the capacity investment strategy under volatile electricity spot price when renewable energy penetration rate is low, taking into account these two conditions.

Design/methodology/approach

The authors design a capacity investment model under dual uncertainties and consider how to optimize the investment capacity in order to maximize profit under two different conditions.

Findings

The authors find that when renewable energy supply fluctuation is unrelated to spot electricity price fluctuation, the renewable energy power profitability is determined by the average cost of spot electricity price and equivalent cost. When renewable energy supply fluctuation is related to spot electricity price fluctuation, the renewable energy power profitability is determined by the market value and the construction and maintenance cost.

Practical implications

Faced with the conflict of the renewable energy supply, the authors need to understand how to plan the generation capacity with intermittent renewable sources. The result helps renewable energy become competitive in the electricity market under loose regulations.

Originality/value

The authors compare two capacity investment strategies that the renewable energy supply fluctuation is related and unrelated to spot electricity price.

Details

Industrial Management & Data Systems, vol. 117 no. 6
Type: Research Article
ISSN: 0263-5577

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Article
Publication date: 20 November 2009

Diana F. Spears, David R. Thayer and Dimitri V. Zarzhitsky

In light of the current international concerns with security and terrorism, interest is increasing on the topic of using robot swarms to locate the source of chemical…

Abstract

Purpose

In light of the current international concerns with security and terrorism, interest is increasing on the topic of using robot swarms to locate the source of chemical hazards. The purpose of this paper is to place this task, called chemical plume tracing (CPT), in the context of fluid dynamics.

Design/methodology/approach

This paper provides a foundation for CPT based on the physics of fluid dynamics. The theoretical approach is founded upon source localization using the divergence theorem of vector calculus, and the fundamental underlying notion of the divergence of the chemical mass flux. A CPT algorithm called fluxotaxis is presented that follows the gradient of this mass flux to locate a chemical source emitter.

Findings

Theoretical results are presented confirming that fluxotaxis will guide a robot swarm toward chemical sources, and away from misleading chemical sinks. Complementary empirical results demonstrate that in simulation, a swarm of fluxotaxis‐guided mobile robots rapidly converges on a source emitter despite obstacles, realistic vehicle constraints, and flow regimes ranging from laminar to turbulent. Fluxotaxis outperforms the two leading competitors, and the theoretical results are confirmed experimentally. Furthermore, initial experiments on real robots show promise for CPT in relatively uncontrolled indoor environments.

Practical implications

A physics‐based approach is shown to be a viable alternative to existing mainly biomimetic approaches to CPT. It has the advantage of being analyzable using standard physics analysis methods.

Originality/value

The fluxotaxis algorithm for CPT is shown to be “correct” in the sense that it is guaranteed to point toward a true source emitter and not be fooled by fluid sinks. It is experimentally (in simulation), and in one case also theoretically, shown to be superior to its leading competitors at finding a source emitter in a wide variety of challenging realistic environments.

Details

International Journal of Intelligent Computing and Cybernetics, vol. 2 no. 4
Type: Research Article
ISSN: 1756-378X

Keywords

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Book part
Publication date: 9 February 2004

Abstract

Details

Economic Complexity
Type: Book
ISBN: 978-0-44451-433-2

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Article
Publication date: 4 September 2018

Kavitha Muppala Kumar, Kavitha A. and Christilda Nancy Duraisamy John

In the design and development stage of the power converter systems, an abnormal intermittency is naturally experienced in nonautonomous system because of coupling of the…

Abstract

Purpose

In the design and development stage of the power converter systems, an abnormal intermittency is naturally experienced in nonautonomous system because of coupling of the interference signals. The study of identifying the possible conditions at which such an undesirable operation emerges is vital. Hence, the purpose of this paper is to explore the intermittent instabilities that evolve in the voltage-mode controlled quadratic buck converter when the sinusoidal interference signal coupled in reference voltage.

Design/methodology/approach

Voltage-mode controlled quadratic buck converter with the sinusoidal interference signal coupled in reference voltage manifests a symmetrical period-doubling bifurcation in intermittent periods for significant interference signal strength with the frequency near to the switching frequency or its rational multiples. The complete dynamics of the system is investigated for the various inference signal frequencies by numerical simulations.

Findings

Here, the intermittent instabilities are verified using a simple Filippov’s method with supporting evidence of Floquet multipliers (eigenvalues) movement. The analytical result obtained is found to agree well with the simulation results.

Practical implications

Power supplies are liable to an ambiguous complex behavior when it is seldom protected against the interference signal. The experimental study has made an attempt to explicit a detailed behavior observed in voltage-mode controlled quadratic buck converter when a sinusoidal intruding signal of different amplitude and frequency are coupled with the reference voltage. Such an analysis gives considerable focus for the power electronics engineers to meet the design requirements.

Originality/value

To the authors’ knowledge, all the research works on intermittent instabilities in power converters are analyzed only using conventional method of Poincare map technique which emerges to be complicated when the order of the system is higher. Alternatively, in this paper, Filippov’s technique is used for stability analysis of periodic orbit. The evolution of bifurcation point is predicted by the calculating the Floquet multipliers of monodromy matrix, and it is known to achieve the same objective as the Poincare map technique in much more straightforward way.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 37 no. 6
Type: Research Article
ISSN: 0332-1649

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Article
Publication date: 1 March 1993

Antonio Garciá‐Olivares

The concept of self‐organization proposed by Von Foerster and developed recently by I. Prigogine and the “synergetics” of H. Haken state a framework that promises to be…

Abstract

The concept of self‐organization proposed by Von Foerster and developed recently by I. Prigogine and the “synergetics” of H. Haken state a framework that promises to be fruitful in the construction of theories synthesizing the microscale and the macroscale points of view in complex systems. This concept may be especially interesting in human sciences, like sociology, where the duality microsociology/ macrosociology remains. Tries to identify explicitly the main features defining the self‐organization of microelements that produce a macroscopic system, and applies the concept to phenomena of social evolution, suggesting a formulation of the micro/macro relationship in social sciences in terms of the probabilistic field theory.

Details

Kybernetes, vol. 22 no. 3
Type: Research Article
ISSN: 0368-492X

Keywords

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Article
Publication date: 28 May 2021

Zhenning Zhu, Lingcheng Kong, Gulizhaer Aisaiti, Mingzhen Song and Zefeng Mi

In the hybrid electricity market consisting of renewable and conventional energy, the generation output of renewable power is uncertain because of its intermittency, and…

Abstract

Purpose

In the hybrid electricity market consisting of renewable and conventional energy, the generation output of renewable power is uncertain because of its intermittency, and the power market demand is also fluctuant. Meanwhile, there is fierce competition among power producers in the power supply market and retailers in the demand market after deregulation, which increases the difficulty of renewable energy power grid-connection. To promote grid-connection of renewable energy power in the hybrid electricity market, the authors construct different contract decision-making models in the “many-to-many” hybrid power supply chain to explore the pricing strategy of renewable energy power grid-connecting.

Design/methodology/approach

Considering the dual-uncertainty of renewable energy power output and electricity market demand, the authors construct different decision-making models of wholesale price contract and revenue-sharing contract to compare and optimize grid-connecting pricing, respectively, to maximize the profits of different participants in the hybrid power supply chain. Besides, the authors set different parameters in the models to explore the influence of competition intensity, government subsidies, etc. on power pricing. Then, a numerical simulation is carried out, they verify the existence of the equilibrium solutions satisfying the supply chain coordination, compare the differences of pricing contracts and further analyze the variation characteristics of optimal contract parameters and their interaction relations.

Findings

Revenue-sharing contract can increase the quantity of green power grid-connection and realize benefits Pareto improvement of all parties in hybrid power supply chain. The competition intensity both of power supply and demand market will have an impact on the sharing ratio, and the increase of competition intensity results in a reduction of power supply chain coordination pressure. The power contract price, spot price and selling price have all been reduced with the increase of the sharing ratio, and the price of renewable power is more sensitive to the ratio change. The sharing ratio shows a downward trend with the increase of government green power subsidies.

Originality/value

On the basis of expanding the definition of hybrid power market and the theory of newsvendor model, considering the dual-uncertainty of green power generation output and electricity market demand, this paper builds and compares different contract decision-making models to study the grid-connection pricing strategy of renewable energy power. And as an extension of supply chain structure types and management, the authors build a “many-to-many” power supply chain structure model and analyze the impact of competition intensity among power enterprises and the government subsidy on the power grid-connecting pricing.

Details

Industrial Management & Data Systems, vol. 121 no. 7
Type: Research Article
ISSN: 0263-5577

Keywords

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