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Article
Publication date: 6 November 2017

Mojtaba Tahani, Mehran Masdari, Hamidreza Eivazi and Massoud Tatar

This paper aims to investigate numerical solution of transonic flow around NACA0012 airfoil under sinusoidal pitch oscillation. Accordingly, effects of the amplitude and…

Abstract

Purpose

This paper aims to investigate numerical solution of transonic flow around NACA0012 airfoil under sinusoidal pitch oscillation. Accordingly, effects of the amplitude and frequency of oscillations on aerodynamic coefficients are evaluated and the efficiency of the turbulent models, K-ω shear-stress transport (SST), scale adaptive simulation (SAS) and delayed detached eddy simulation (DDES), in simulation of the nonlinear phenomena – i.e. the interaction between shock and boundary layer and the shock oscillations – is studied.

Design/methodology/approach

K-ω SST, SAS and DDES models are used as turbulence approaches. The numerical results are compared with available experimental and numerical information.

Findings

According to the results inside the buffet boundaries, the DDES turbulent model expresses results that are more appropriate; however, SAS and SST models are not efficient enough in evaluating the characteristics of nonlinear flow.

Originality/value

In this research study, hybrid RANS-LES turbulence model is engaged to simulate transonic flow around pitching NACA0012 airfoil, and results are compared to the SAS and Reynolds Average Navier–Stocks simulations as well as available numerical and experimental data. In addition, effects of the amplitude and frequency of oscillations on aerodynamic coefficients are evaluated in buffet regions.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 27 no. 11
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 4 September 2017

Marcello Righi

The quality of aeroelastic predictions strongly depends on the quality of aerodynamic predictions. At the boundary of a typical flight envelope, special flow conditions…

Abstract

Purpose

The quality of aeroelastic predictions strongly depends on the quality of aerodynamic predictions. At the boundary of a typical flight envelope, special flow conditions may arise, which challenge the conventional Reynolds-averaged Navier–Stokes (RANS) approach beyond reasonable limits.

Design/methodology/approach

Test Case 3 of the Second AIAA Aeroelastic Prediction Workshop is a representative test case, where the flow over a supercritical wing separates downstream of the shock waves and generates large turbulent lengthscales.

Findings

In this study, RANS predictions are compared to those obtained in this particular test case with the more sophisticated hybrid RANS–large eddy simulation (LES) approach, in particular with the Spalart–Allmaras–delayed detached eddy simulation model. Results are indeed closer to experimental data.

Originality/value

However, the costs associated with this approach are much higher. It is argued that adopting hybrid RANS–LES modelling is not a simple model switch.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 5
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 19 June 2019

Jéromine Dumon, Yannick Bury, Nicolas Gourdain and Laurent Michel

The development of reusable space launchers requires a comprehensive knowledge of transonic flow effects on the launcher structure, such as buffet. Indeed, the mechanical…

Abstract

Purpose

The development of reusable space launchers requires a comprehensive knowledge of transonic flow effects on the launcher structure, such as buffet. Indeed, the mechanical integrity of the launcher can be compromised by shock wave/boundary layer interactions, that induce lateral forces responsible for plunging and pitching moments.

Design/methodology/approach

This paper aims to report numerical and experimental investigations on the aerodynamic and aeroelastic behavior of a diamond airfoil, designed for microsatellite-dedicated launchers, with a particular interest for the fluid/structure interaction during buffeting. Experimental investigations based on Schlieren visualizations are conducted in a transonic wind tunnel and are then compared with numerical predictions based on unsteady Reynolds averaged Navier–Stokes and large eddy simulation (LES) approaches. The effect of buffeting on the structure is finally studied by solving the equation of the dynamics.

Findings

Buffeting is both experimentally and numerically revealed. Experiments highlight 3D oscillations of the shock wave in the manner of a wind-flapping flag. LES computations identify a lambda-shaped shock wave foot width oscillations, which noticeably impact aerodynamic loads. At last, the experiments highlight the chaotic behavior of the shock wave as it shifts from an oscillatory periodic to an erratic 3D flapping state. Fluid structure computations show that the aerodynamic response of the airfoil tends to damp the structural vibrations and to mitigate the effect of buffeting.

Originality/value

While buffeting has been extensively studied for classical supercritical profiles, this study focuses on diamond airfoils. Moreover, a fluid structure computation has been conducted to point out the effect of buffeting.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 9
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 2 November 2018

Jernej Drofelnik, Andrea Da Ronch, Matteo Franciolini and Andrea Crivellini

This paper aims to present a numerical method based on computational fluid dynamics that allows investigating the buffet envelope of reference equivalent wings at the…

Abstract

Purpose

This paper aims to present a numerical method based on computational fluid dynamics that allows investigating the buffet envelope of reference equivalent wings at the equivalent cost of several two-dimensional, unsteady, turbulent flow analyses. The method bridges the gap between semi-empirical relations, generally dominant in the early phases of aircraft design, and three-dimensional turbulent flow analyses, characterised by high costs in analysis setups and prohibitive computing times.

Design/methodology/approach

Accuracy in the predictions and efficiency in the solution are two key aspects. Accuracy is maintained by solving a specialised form of the Reynolds-averaged Navier–Stokes equations valid for infinite-swept wing flows. Efficiency of the solution is reached by a novel implementation of the flow solver, as well as by combining solutions of different fidelity spatially.

Findings

Discovering the buffet envelope of a set of reference equivalent wings is accompanied with an estimate of the uncertainties in the numerical predictions. Just over 2,000 processor hours are needed if it is admissible to deal with an uncertainty of ±1.0° in the angle of attack at which buffet onset/offset occurs. Halving the uncertainty requires significantly more computing resources, close to a factor 200 compared with the larger uncertainty case.

Practical implications

To permit the use of the proposed method as a practical design tool in the conceptual/preliminary aircraft design phases, the method offers the designer with the ability to gauge the sensitivity of buffet on primary design variables, such as wing sweep angle and chord to thickness ratio.

Originality/value

The infinite-swept wing, unsteady Reynolds-averaged Navier–Stokes equations have been successfully applied, for the first time, to identify buffeting conditions. This demonstrates the adequateness of the proposed method in the conceptual/preliminary aircraft design phases.

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Article
Publication date: 5 September 2016

Fulvio Sartor and Sebastian Timme

The purpose of this paper is to discuss a numerical study of the flow over a wing representative of a large civil aircraft at cruise condition. For each Mach number…

Abstract

Purpose

The purpose of this paper is to discuss a numerical study of the flow over a wing representative of a large civil aircraft at cruise condition. For each Mach number considered, the numerical simulations indicate that critical angle of attack exists where the separated region increases in size and begins to oscillate. This phenomenon, known as transonic shock buffet, is reproduced by the unsteady simulation and much information can be extracted analysing location, amplitude and frequency content of the unsteadiness.

Design/methodology/approach

Reynolds-averaged Navier-Stokes simulations are conducted on a half wing-body configuration, at different Mach numbers and angles of attack. Different turbulence models are considered, and both steady-state results and time-accurate simulations are discussed.

Findings

The high number of cases presented in this study allows the creation of a database which, to the authors’ knowledge, has not been documented in literature before. The results indicate that, while high-fidelity approaches can improve the quality of the results, the URANS approach is capable of describing the main features of the buffet phenomenon.

Research limitations/implications

The presence of a turbulence model, despite allowing the description of the main unsteady phenomenon, might be insufficient to fully characterise the unsteadiness present in a transonic flow over a half wing-body configuration. Therefore, researchers are encouraged to verify by means of experimental investigation or high-fidelity approach the results issued from a Reynolds-averaged Navier-Stokes equations.

Practical implications

The results presented clearly indicate that, despite what proposed in recent research papers, transonic buffet can be described by means of time-accurate Reynolds-averaged Navier-Stokes equations. Such an approach is popular in the aeronautical industry because of its reduced costs, and could be used for wing design.

Originality/value

In this paper, the authors used a classical approach to tackle the known problem of transonic buffet in three-dimensional configurations. The large number of results presented can be used as a database for future numerical simulations and experiments, and allow to describe the flow-physics of the buffet unsteadiness on a half wing-body configuration.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 26 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

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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

Keywords

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Article
Publication date: 18 December 2020

Titus Ayobami Ojeyinka and Dauda Olalekan Yinusa

The study investigates the impact of external shocks on output composition (consumption and investment) in Nigeria for the period 1981:Q1– 2018:Q4. Trade-weighted…

Abstract

Purpose

The study investigates the impact of external shocks on output composition (consumption and investment) in Nigeria for the period 1981:Q1– 2018:Q4. Trade-weighted variables from the country's five major trading partners are constructed to capture the impact.

Design/methodology/approach

The study employs a block exogeneity open economy structural vector autoregressive (SVAR) analysis in studying the stated relationship.

Findings

The study reveals that external shocks significantly affect consumption and investment in Nigeria. Results from the structural impulse response function suggest that foreign output, real effective exchange rate and foreign interest rate have significant negative effects on consumption and investment. Specifically, results from error variance decomposition show that foreign inflation and real effective exchange rate shocks are major drivers of fluctuations in consumption and investment in Nigeria. Interestingly, the study finds that oil price shock accounts for minor variations in consumption and investment in Nigeria.

Research limitations/implications

The findings suggest that consumption and investment in Nigeria are substantially and largely driven by external shocks.

Practical implications

There is need for the monetary authority and the Nigerian government to design appropriate policies to stabilise the naira and salvage the country's exchange rate from unexpected large swings so as to reduce the vulnerability of the economy to external shocks.

Originality/value

Previous studies on external shocks have concentrated on the impact of external shocks on aggregate variables such as output and inflation, while few studies on external shocks in Nigeria capture external shocks through single-country data. This study differs from previous similar studies in Nigeria in two ways. First, the study examines the impact of external shocks on output composition such as consumption and investment. Second, the study captures the impact of external shocks on the two components of gross domestic product (GDP) by constructing trade-weighted variables from Nigeria's five major trading partners.

Details

Journal of Economic and Administrative Sciences, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1026-4116

Keywords

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Article
Publication date: 26 July 2021

Francesco Capizzano and Triyantono Sucipto

This paper aims to describe a research effort towards the comprehension of the unsteady phenomena due to the deployment of high-lift devices at approach/landing conditions.

Abstract

Purpose

This paper aims to describe a research effort towards the comprehension of the unsteady phenomena due to the deployment of high-lift devices at approach/landing conditions.

Design/methodology/approach

The work starts from a preexisting platform based on an immersed boundary (IB) method whose capabilities are extended to study compressible and viscous flows around moving/deforming objects. A hybrid Lagrangian-Eulerian approach is designed to consider the motion of multiple bodies through a fixed Cartesian mesh. That is, the cells’ volumes do not move in space but rather they observe the solid walls crossing themselves. A dynamic discrete forcing makes use of a moving least-square procedure which has been validated by simulating well-known benchmarks available for rigid body motions. Partitioned fluid-structure interactions (FSI) strategies are explored to consider aeroelastic phenomena. A shared platform, between the aerodynamic and the structural solvers, fulfils the loads’ transfer and drives the sequence of the operating steps.

Findings

The first part of the results is devoted to a basic two-dimensional study aiming at evaluating the accuracy of the method when simple rigid motions are prescribed. Afterwards, the paper discusses the solution obtained when applying the dynamic IB method to the rigid deployment of a Krueger-flap. The final section discusses the aeroelastic behaviour of a three-element airfoil during its deployment phase. A loose FSI coupling is applied for estimating the possible loads’ downgrade.

Research limitations/implications

The IB surfaces are allowed to move less than one IB-cell size at each time-step de-facto restricting the Courant-Friedrichs-Lewy (CFL) based on the wall velocity to be smaller than unity. The violation of this constraint would impair the explicit character of the method.

Practical implications

The proposed method improves automation in FSI numerical analysis and relaxes the human expertise/effort for meshing the computational domain around complex three-dimensional geometries. The logical consequence is an overall speed-up of the simulation process.

Originality/value

The value of the paper consists in demonstrating the applicability of dynamic IB techniques for studying high-lift devices. In particular, the proposed Cartesian method does not want to compete with body-conforming ones whose accuracy remains generally superior. Rather, the merit of this research is to propose a fast and automatic simulation system as a viable alternative to classic multi-block structured, chimaera or unstructured tools.

Details

Aircraft Engineering and Aerospace Technology, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 1 June 2004

N. Qin, Y. Zhu and S.T. Shaw

In this paper, the effectiveness of a number of active devices for the control of shock waves on transonic aerofoils is investigated using numerical solutions of the…

Abstract

In this paper, the effectiveness of a number of active devices for the control of shock waves on transonic aerofoils is investigated using numerical solutions of the Reynolds‐averaged Navier‐Stokes equations. A brief description of the flow model and the numerical method is presented including, in particular, the boundary condition modelling and the numerical treatment for surface mass transfer. Comparisons with experimental data have been made where possible to validate the numerical study before some systematic numerical simulations for a parametric study. The effects of surface suction, blowing, and local modification of the surface contour (bump) on aerofoil aerodynamic performance have been studied extensively regarding the control location, the mass flow strength and the bump height. The numerical simulations highlight the benefits and drawbacks of the various control devices for transonic aerodynamic performance and identify the key design parameters for optimisation.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 14 no. 4
Type: Research Article
ISSN: 0961-5539

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Book part
Publication date: 4 December 2018

Indranarain Ramlall

Abstract

Details

Understanding Financial Stability
Type: Book
ISBN: 978-1-78756-834-1

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