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Article
Publication date: 10 April 2020

Wienczyslaw Stalewski and Katarzyna Surmacz

This paper aims to present the novel methodology of computational simulation of a helicopter flight, developed especially to investigate the vortex ring state (VRS) – a dangerous…

Abstract

Purpose

This paper aims to present the novel methodology of computational simulation of a helicopter flight, developed especially to investigate the vortex ring state (VRS) – a dangerous phenomenon that may occur in helicopter vertical or steep descent. Therefore, the methodology has to enable modelling of fast manoeuvres of a helicopter such as the entrance in and safe escape from the VRS. The additional purpose of the paper is to discuss the results of conducted simulations of such manoeuvres.

Design/methodology/approach

The developed methodology joins several methods of computational fluid dynamics and flight dynamic. The approach consists of calculation of aerodynamic forces acting on rotorcraft, by solution of the unsteady Reynold-averaged Navier–Stokes (URANS) equations using the finite volume method. In parallel, the equations of motion of the helicopter and the fluid–structure-interaction equations are solved. To reduce computational costs, the flow effects caused by rotating blades are modelled using a simplified approach based on the virtual blade model.

Findings

The developed methodology of computational simulation of fast manoeuvres of a helicopter may be a valuable and reliable tool, useful when investigating the VRS. The presented results of conducted simulations of helicopter manoeuvres qualitatively comply with both the results of known experimental studies and flight tests.

Research limitations/implications

The continuation of the presented research will primarily include quantitative validation of the developed methodology, with respect to well-documented flight tests of real helicopters.

Practical implications

The VRS is a very dangerous phenomenon that usually causes a sudden decrease of rotor thrust, an increase of the descent rate, deterioration of manoeuvrability and deficit of power. Because of this, it is difficult and risky to test the VRS during the real flight tests. Therefore, the reliable computer simulations performed using the developed methodology can significantly contribute to increase helicopter flight safety.

Originality/value

The paper presents the innovative and original methodology for simulating fast helicopter manoeuvres, distinguished by the original approach to flight control as well as the fact that the aerodynamic forces acting on the rotorcraft are calculated during the simulation based on the solution of URANS equations.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 9
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 1 April 1952

L.H. Hay ward

ACCORDING to historical records the earliest known drawings for an aerial machine that can be classified under the heading of helicopter were made in the fifteenth century by the…

Abstract

ACCORDING to historical records the earliest known drawings for an aerial machine that can be classified under the heading of helicopter were made in the fifteenth century by the world renowned Italian scientist and artist Leonardo da Vinci (1452–1519). Probably the Chinese had been making their helicopter toy for some considerable time before da Vinci commenced his experiments. This toy consisted of two feathers, joined together by means of a cork or soft wood boss, to form a crude type of propeller which was pushed up a threaded stick so that upon leaving the stick the propeller rotated at high speed and continued to screw itself up in the air. When the speed of rotation decreased the propeller slowly windmilled down to the ground. A similar toy is still being sold today.

Details

Aircraft Engineering and Aerospace Technology, vol. 24 no. 4
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 19 June 2019

Seyed Hamid Delbari, Amir Nejat, Mohammad H. Ahmadi, Ali Khaleghi and Marjan Goodarzi

This study aims to carry out numerical modeling to predict aerodynamic noise radiation from four different Savonius rotor blade profile.

Abstract

Purpose

This study aims to carry out numerical modeling to predict aerodynamic noise radiation from four different Savonius rotor blade profile.

Design/methodology/approach

Incompressible unsteady reynolds-averaged navier-stokes (URANS) approach using gamma–theta turbulence model is conducted to obtain the time accurate turbulent flow field. The Ffowcs Williams and Hawkings (FW-H) acoustic analogy formulation is used for noise predictions at optimal tip speed ratio (TSR).

Findings

The mean torque and power coefficients are compared with the experimental data and acceptable agreement is observed. The total and Mono+Dipole noise graphs are presented. A discrete tonal component at low frequencies in all graphs is attributed to the blade passing frequency at the given TSR. According to the noise prediction results, Bach type rotor has the lowest level of noise emission. The effect of TSR on the noise level from the Bach rotor is investigated. A direct relation between angular velocity and the noise emission is found.

Practical implications

The savonius rotor is a type of vertical axis wind turbines suited for mounting in the vicinity of residential areas. Also, wind turbines wherein operation are efficient sources of tonal and broadband noises and affect the inhabitable environment adversely. Therefore, the acoustic pollution assessment is essential for the installation of wind turbines in residential areas.

Originality/value

This study aims to investigate the radiated noise level of four common Savonius rotor blade profiles, namely, Bach type, Benesh type, semi-elliptic and conventional. As stated above, numbers of studies exploit the URANS method coupled with the FW-H analogy to predict the aeroacoustics behavior of wind turbines. Therefore, this approach is chosen in this research to deal with the aeroacoustics and aerodynamic calculation of the flow field around the aforementioned Savonius blade profiles. The effect of optimal TSR on the emitted noise and the contribution of thickness, loading and quadrupole sources are of interest in this study.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 10 October 2016

Santosh Kumar Choudhary

The purpose of this paper is to investigate an optimal control solution with prescribed degree of stability for the position and tracking control problem of the twin rotor

Abstract

Purpose

The purpose of this paper is to investigate an optimal control solution with prescribed degree of stability for the position and tracking control problem of the twin rotor multiple input-multiple output (MIMO) system (TRMS). The twin rotor MIMO system is a benchmark aerodynamical laboratory model having strongly non-linear characteristics and unstable coupling dynamics which make the control of such system for either posture stabilization or trajectory tracking a challenging task.

Design/methodology/approach

This paper first describes the dynamical model of twin rotor MIMO system (TRMS) and then it adopts linear-quadratic regulator (LQR)-based optimal control technique with prescribed degree of stability to achieve the desired trajectory or posture stabilization of TRMS.

Findings

The simulation results show that the investigated controller has both static and dynamic performance; therefore, the stability and the quick control effect can be obtained simultaneously for the twin rotor MIMO system.

Originality/value

The articles on LQR optimal controllers for TRMS can also be found in many literatures, but the prescribed degree of stability concept was not discussed in any of the paper. In this work, new LQR with the prescribed degree of stability concept is applied to provide an optimal control solution for the position and tracking control problem of TRMS.

Details

International Journal of Intelligent Unmanned Systems, vol. 4 no. 4
Type: Research Article
ISSN: 2049-6427

Keywords

Article
Publication date: 10 August 2012

Idriss El‐Thalji and Jayantha P. Liyanage

The purpose of this paper is to review the operation and maintenance practices within wind power applications and to clarify practical needs as gaps between researchers and…

2342

Abstract

Purpose

The purpose of this paper is to review the operation and maintenance practices within wind power applications and to clarify practical needs as gaps between researchers and practitioners.

Design/methodology/approach

The paper collects, categorizes, and analyzes the published literature of both researchers and practitioners systematically.

Findings

The paper defines significant issues in operation and maintenance of wind energy related to: site and seasonal asset disturbances; stakeholders’ requirements trade‐off; dependability and asset deterioration challenges; diagnostic, prognostic and information and communication technologies (ICTs) applications; and maintenance optimization models. Within each category, the gaps and further research needs have been extracted with respect to both an academic and industrial perspective.

Practical implications

The use of wind energy is growing rapidly and the associated practices related to maintenance and asset management are still lacking. Therefore, the literature review of operation and maintenance is a necessity to uncover the holistic issues and interrelationships of what has so far been published as detailed and fragmented topics to specific issues. Wind energy assets represent modern renewable energy assets which are affected by environmental disturbances, rapid technological development, rapid scaling‐up processes, the stochastic and dynamic nature of operations and degradation, the integrity and interoperability of system‐to‐support.

Originality/value

The paper provides a comprehensive review of research contributions and industrial development efforts. That will be useful to the life cycle stakeholders in both academia and industry in understanding the maintenance problem and solution space within the wind energy context.

Article
Publication date: 8 May 2009

Sławomir Wiak and Krzysztof Smółka

The purpose of this paper is to discuss the numerical modelling of 3D structure of micro‐electro‐mechanical systems (MEMS) accelerometers. The general idea being discussed is the…

Abstract

Purpose

The purpose of this paper is to discuss the numerical modelling of 3D structure of micro‐electro‐mechanical systems (MEMS) accelerometers. The general idea being discussed is the method of levitation force reduction, as the main source of incorrect mathematical model of comb drive structure.

Design/methodology/approach

Accelerometers design is a highly interdisciplinary area and, therefore, different methods and tools have to be exploited. Dynamic accelerometer behaviour modelling has been performed by use of a new object‐oriented model (NOOM), based on complex computer field and mechanical models.

Findings

The paper describes methods of levitation force reduction in electrostatic comb drive structures based on electrostatic structural models and finite elements method.

Research limitations/implications

In the present work, the authors limit themselves to the electrostatic energy domains.

Practical implications

Both, mechanical and electric models of accelerometers give the input data for defining the object‐oriented model, based on Matlab‐Simulink platform, fulfilling the general demand of dynamic behaviour simulation of comb drive structure. The proposed by authors methodology could give valuable contribution to MEMS design methodology.

Originality/value

A new methodology has been successfully applied to calculation of levitation force in different geometries of comb drive. This methodology could be useful for multidisciplinary MEMS systems.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 28 no. 3
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 3 October 2019

Changmin Chen, Jianping Jing and Jiqing Cong

The infinitesimal perturbation (IP) method is commonly used in calculating stiffness and damping of journal bearing in horizon rotor systems. The boundary condition (BC) for the…

158

Abstract

Purpose

The infinitesimal perturbation (IP) method is commonly used in calculating stiffness and damping of journal bearing in horizon rotor systems. The boundary condition (BC) for the perturbed pressure is assumed being zero at leading edge of film, although it is usually not zero because of nonzero pressure gradient. This assumption is sufficiently accurate for most purpose in horizon rotors. However, for journal bearing in vertical rotor-bearing systems, the BC with the assumption in IP method will bring in significant errors in calculating linear dynamic coefficients. This paper aims to propose a method to obtain the dynamic coefficients of journal bearing in vertical rotors.

Design/methodology/approach

The stiffness and damping are approached based on IP method and the modified BC of perturbed pressure. As it is difficult to predict perturbed pressure at leading edge at a fixed coordinate system using IP method, a dynamic coordinate system is introduced in this method, of which the origin on circumferential direction is defined as the leading edge of film.

Findings

The effectiveness and accuracy of proposed IP method in dynamic coordinate (IPMDC) system are verified by comparing the obtained results with analytical solutions. The comparison shows that the results from IPMDC present a good agreement with the analytic solutions.

Originality/value

The proposed method can be applied in obtaining linear dynamic coefficients of journal bearing in vertical rotors with high precisions. Instead of the usual nonlinear analysis of vertical rotors, this method provides a feasibility of predicting the instability threshold of vertical rotor-bearing systems via linear models.

Details

Industrial Lubrication and Tribology, vol. 72 no. 1
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 18 October 2021

Fan Zhang, Peng Yin, Yuyang Liu and Jianmei Wang

The purpose of this paper is to study the influence of pivot stiffness on the dynamic characteristics of tilting-pad journal bearings (TPJBs) and the stability of the bearing-rotor

Abstract

Purpose

The purpose of this paper is to study the influence of pivot stiffness on the dynamic characteristics of tilting-pad journal bearings (TPJBs) and the stability of the bearing-rotor system.

Design/methodology/approach

A theoretical numerical model is established, and the influences of pivot stiffness on TPJBs and a bearing-rotor system are analyzed. Then, two kinds of pivot structures with different stiffness are designed and the vibration characteristics are tested on the vertical rotor bearing test bench.

Findings

The pivot stiffness has an obvious effect on the dynamic characteristics of the TPJBs and the stability of the bearing-rotor system. As a result of appropriate pivot stiffness, the critical speed and the vibration amplification factor can be reduced, the logarithmic decay rate and the stability of the rotor system can be effectively increased. While the journal whirl orbit is smoother and the rubbing is obviously reduced when the bearings have flexible pivots.

Originality/value

The influence of pivot stiffness on TPJBs and a vertical rotor-bearing system is studied by theoretical and experimental methods.

Details

Industrial Lubrication and Tribology, vol. 73 no. 10
Type: Research Article
ISSN: 0036-8792

Keywords

Article
Publication date: 1 March 1956

P.R. Payne

AT low forward speeds the slipstream from a helicopter rotor is substantially downwards in direction and will cause a drag force to be generated on any body immersed in it, the…

Abstract

AT low forward speeds the slipstream from a helicopter rotor is substantially downwards in direction and will cause a drag force to be generated on any body immersed in it, the drag acting in the direction of the slipstream. In most performance methods the effect of this vertical drag is ignored, bat it cart in fact substantially modify calculated performance, being equivalent to a weight increase of over 10 per cent even on some single rotor designs. The basic parameter is the equivalent flat plate area (area of body drag coefficient) which is immersed in the slipstream, and this is expressed as a ratio of the rotor disk area, i.e. ACD/πR2.

Details

Aircraft Engineering and Aerospace Technology, vol. 28 no. 3
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 1 November 1963

H.L. Price

The component of velocity, μ0ΩR, along the x‐axis is specified, and also X, the angle of inclination of the flight path. The concept of the ‘internal’ and ‘external’ parameters…

Abstract

The component of velocity, μ0ΩR, along the x‐axis is specified, and also X, the angle of inclination of the flight path. The concept of the ‘internal’ and ‘external’ parameters of the motion is introduced, the ‘internal’ parameters consisting of certain combinations of the control and flapping angles θ0, θ1, θ2, β0, β1, β2 and the ‘external’ parameters consisting of μ0, Λ0, Θ, X, ∈ and z*, where Θ is the inclination of the x‐axis to the horizontal, and e the inclination to the vertical of the rotor resultant force‐vector. For a given centre of gravity position of the helicopter the ‘external’ parameters are shown to be determinable independently of the ‘internal’ parameters, subject to certain assumptions regarding the fuselage drag coefficient. The fundamental ‘internal’ parameter then emerges as (β1—Θ), which physically is the fore or aft inclination to the vertical of the rotor cone axis. The value of this parameter is found as the root of a quadratic equation, and not a linear equation as hitherto. It is shown that at high values of μ0 the rotor force‐vector docs not coincide with the rotor cone axis (as it is commonly supposed to do), the difference between (β1—Θ) and ∈ amounting possibly to 5 deg., of which no more than 1½ deg. can be accounted for by the rotor mean drag force component. Particular attention is paid to the case of horizontal flight, in which the true speed is μ0ΩR see Θ, the factor sec Θ being important. It is shown that at a given true speed the following quantities are independent of the centre of gravity position of the helicopter: (i) ∈, (ii) the quantity (λ1—Λ0+λ0β1), i.e. the component of the air velocity along the rotor cone axis, (iii) the horse‐power of the engine. In addition the following ‘internal’ parameters, (iv) (β1—Θ), (v) (θ2—β1), (vi) (θ1—β2), are very nearly independent of C.G. position, their variations with C.G. position only just becoming noticeable at large values of μ0. This feature enables a much simplified solution to the trim problem to be obtained by working in terms of a fictitious C.G. position chosen to make Θ zero. The genuinely C.G.‐sensitive parameters θ1, θ2, β1, β2 and Θ are subsequently converted to their true values corresponding to the actual C.G. position. The effect of variation in blade moment of inertia is examined through variations in the associated parameter γ, and it is shown that both the ‘external’ and ‘internal’ conditions are substantially unaltered, save for (θ1+ β2) and the mean coning angle β0, which do vary considerably with γ. The analysis is accurate at least so far as μ05 and the results are shown to be consistent with an energy equation. The only sources of error in the dynamics of the problem lie in the rejection of higher powers of μ0 and of flapping harmonics of β beyond the first. In order to assess the effects of this rejection, an analysis is made of a rigid rotor system free only to feather without flapping, and an exact dynamical solution for horizontal flight is obtained, subject to the same aerodynamical assumptions as before. At a given value of μ0 see Θ the results differ slightly from the case of the flapping rotor because now the purely feathering rotor applies a pitching couple mechanically to the fuselage via the shaft, which the flapping rotor is not able to do. However, by calculating the value of this couple, and supposing that the helicopter with the flapping rotor experiences either an aerodynamic fuselage pitching moment of the same amount or alternatively an appropriate C.G. shift, the two cases are reduced to essentially equivalent physical systems, particularly if the mean coning angle, β0, is deliberately arranged to be zero by proper choice of γ. A recalculation of the flapping case is then made; if its theory were exact, its solution would coincide with the known exact solution of the purely feathering rotor case. The discrepancies are shown to be very small, and thus the validity of rejecting μ06 is established for the earlier flapping rotor analysis. Part III is concerned with the theoretical solution of the feathering‐cumflapping rotor case, and also with a geometrical account of the trim configuration. Part IV contains the solution for the purely feathering rotor together with a discussion of the large number of numerical results and related tables, obtained on a Pegasus Computer.

Details

Aircraft Engineering and Aerospace Technology, vol. 35 no. 11
Type: Research Article
ISSN: 0002-2667

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