Search results

1 – 10 of over 2000
To view the access options for this content please click here
Article
Publication date: 12 October 2018

Dimitris Gkiolas, Demetri Yiasemides and Demetri Mathioulakis

The complex flow behavior over an oscillating aerodynamic body, e.g. a helicopter rotor blade, a rotating wind turbine blade or the wing of a maneuvering airplane involves…

Abstract

Purpose

The complex flow behavior over an oscillating aerodynamic body, e.g. a helicopter rotor blade, a rotating wind turbine blade or the wing of a maneuvering airplane involves combinations of pitching and plunging motions. As the parameters of the problem (Re, St and phase difference between these two motions) vary, a quasi-steady analysis fails to provide realistic results for the aerodynamic response of the moving body, whereas this study aims to provide reliable experimental data.

Design/methodology/approach

In the present study, a pitching and plunging mechanism was designed and built in a subsonic closed-circuit wind tunnel as well as a rectangular aluminum wing of a 2:1 aspect-ratio with a NACA64-418 airfoil, used in wind turbine blades. To measure the pressure distribution along the wing chord, a number of fast responding transducers were embedded into the mid span wing surface. Simultaneous pressure measurements were conducted along the wing chord for the Reynolds number of 0.85 × 106 for both steady and unsteady cases (pitching and plunging). A flow visualization technique was used to detect the flow separation line under steady conditions.

Findings

Elevated pressure fluctuations coincide with the flow separation line having been detected through surface flow visualization and flattened pressure distributions appear downstream of the flow separation line. Closed hysteresis loops of the lift coefficient versus angle of attack were measured for combined pitching and plunging motions.

Practical implications

The experimental data can be used for improvement of unsteady fluid mechanics problem solvers.

Originality/value

In the present study, a new installation was built allowing the aerodynamic study of oscillating wings performing pitching and plunging motions with prescribed frequencies and phase lags between the two motions. The experimental data can be used for improvement of computational fluid dynamics codes in case that the examined aerodynamic body is oscillating.

Details

Aircraft Engineering and Aerospace Technology, vol. 90 no. 7
Type: Research Article
ISSN: 1748-8842

Keywords

To view the access options for this content please click here
Article
Publication date: 1 January 1960

P.F. Richards

The general reasons for considering a fresh approach to the calculation of air‐worthiness design tail loads and associated torques due to elevator‐induced pitching

Abstract

The general reasons for considering a fresh approach to the calculation of air‐worthiness design tail loads and associated torques due to elevator‐induced pitching manoeuvres are discussed. Then follows a description of the manoeuvre itself, elevator actions to be assumed, and the proposed method of calculating the various response quantities. The analytical treatment of Czaykowski given to the unchecked manoeuvre is extended to cover the checked case in Appendix I, Part III and a comparison is made of the two types of manoeuvre. The application of the work to auto‐pilot feed‐back failure causing hunting of the elevator control is also dealt with. The effect of aircraft size, weight, e.g. position, forward speed and altitude on the various response quantities are discussed, with particular emphasis on the importance of the manoeuvre margin. To avoid possible confusion of terms the two types of elevator‐induced manoeuvre mentioned above and discussed in this paper are defined as follows:

Details

Aircraft Engineering and Aerospace Technology, vol. 32 no. 1
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article
Publication date: 3 September 2019

Joaquin Ortega-Casanova and Ramon Fernandez-Feria

This paper aims to consider the thrust force generated by two plunging and pitching plates in a tandem configuration in forward flight to find out the configuration that…

Abstract

Purpose

This paper aims to consider the thrust force generated by two plunging and pitching plates in a tandem configuration in forward flight to find out the configuration that maximizes the propulsive efficiency with high-enough time-averaged lift force.

Design/methodology/approach

To that end, the Navier–Stokes equations for the incompressible and two-dimensional flow at Reynolds number $500 are solved. As the number of parameters is quite large, the case of constant separation between the plates (half their chord length), varying seven non-dimensional parameters related to the phase shift between the heaving motion of the foils, the phase lag between pitch and heave of each plate independently and the frequency and amplitude of the heaving and pitching motions are considered. This analysis complements some other recent studies where the separation between the foils has been used as one of the main control parameters.

Findings

It is found that the propulsive efficiency is maximized for a phase shift of 180° (counterstroking), when the reduced frequency is 2.2 and the Strouhal number based on half the plunging amplitude is 0.17, the pitching amplitude is 25° and when pitch leads heave by 135° in both the fore -plate and the hind plate. The propulsive efficiency is about 20 per cent, just a bit larger than that of an isolate plate with the same motion as the fore-plate, but the corresponding lift force is negligible for a single plate. The paper discusses this vortical flow structure in relation to other less efficient ones. Finally, the effect of the separation between the plates and the Reynolds number is also briefly discussed.

Originality/value

The kinematics of two flapping plates in tandem configuration that maximizes the propulsive efficiency are characterized discussing physically the associated vortical flow structures in comparison with less efficient kinematic configurations. A much larger number of parameters in the optimization procedure than in previous related works is considered.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 11
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 19 June 2019

Daniel Klatt, Michael Proff and Robert Hruschka

The present work aims to investigate the capabilities of accurately predicting the six-degrees-of-freedom (6DoF) trajectory and the flight behavior of a flare-stabilized…

Abstract

Purpose

The present work aims to investigate the capabilities of accurately predicting the six-degrees-of-freedom (6DoF) trajectory and the flight behavior of a flare-stabilized projectile using computational fluid dynamics (CFD) and rigid body dynamics (RBD) methods.

Design/methodology/approach

Two different approaches are compared for calculating the trajectory. First, the complete matrix of static and dynamic aerodynamic coefficients for the projectile is determined using static and dynamic CFD methods. This discrete database and the data extracted from free-flight experiments are used to simulate flight trajectories with an in-house developed 6DoF solver. Second, the trajectories are simulated solving the 6DoF motion equations directly coupled with time resolved CFD methods.

Findings

Virtual fly-out simulations using RBD/CFD coupled simulation methods well reproduce the motion behavior shown by the experimental free-flight data. However, using the discrete database of aerodynamic coefficients derived from CFD simulations shows a slightly different flight behavior.

Originality/value

A discrepancy between CFD 6DoF/RBD simulations and results obtained by the MATLAB 6DoF-solver based on discrete CFD data matrices is shown. It is assumed that not all dynamic effects on the aerodynamics of the projectile are captured by the determination of the force and moment coefficients with CFD simulations based on the classical aerodynamic coefficient decomposition.

Details

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

Keywords

To view the access options for this content please click here
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

Keywords

To view the access options for this content please click here
Article
Publication date: 17 August 2015

Yong Cao, Shusheng Bi, Yueri Cai and Yuliang Wang

– This paper aims to develop a robofish with oscillating pectoral fins, and control it to mimic the bionic prototype by central pattern generators (CPGs).

Abstract

Purpose

This paper aims to develop a robofish with oscillating pectoral fins, and control it to mimic the bionic prototype by central pattern generators (CPGs).

Design/methodology/approach

First, the oscillation characteristics of the cownose ray were analyzed quantitatively. Second, a robofish with multi-joint pectoral fins was developed according to the bionic morphology and kinematics. Third, the improved phase oscillator was established, which contains a spatial asymmetric coefficient and a temporal asymmetric coefficient. Moreover, the CPG network is created to mimic the cownose ray and accomplish three-dimensional (3D) motions. Finally, the experiments were done to test the authors ' works.

Findings

The results demonstrate that the CPGs is effective to control the robofish to imitate the cownose ray realistically. In addition, the robofish is able to accomplish 3D motions of high maneuverability, and change among different swimming modes quickly and smoothly.

Originality/value

The research provides the method to develop a robofish from both 3D morphology and kinematics. The motion analysis and CPG control make sure that the robofish has the features of high maneuverability and camouflage. It is useful for military underwater applications and underwater detections in narrow environments. Second, this work lays the foundation for the autonomous 3D control. Moreover, the robotic fish can be taken as a scientific tool for the fluid bionics research.

Details

Industrial Robot: An International Journal, vol. 42 no. 5
Type: Research Article
ISSN: 0143-991X

Keywords

To view the access options for this content please click here
Article
Publication date: 1 January 1932

H.B. Irving and A.V. Stephens

THE purpose of this paper is to give some account of the work on spinning and the progress which has been made since S. B. Gates and L. W. Bryant presented their paper to…

Abstract

THE purpose of this paper is to give some account of the work on spinning and the progress which has been made since S. B. Gates and L. W. Bryant presented their paper to the Society, which was published in more comprehensive form by the Aeronautical Research Committee as R. & M. 1001.

Details

Aircraft Engineering and Aerospace Technology, vol. 4 no. 1
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article
Publication date: 1 February 1939

J.H. Crowe

In this paper a comprehensive survey of spinning phenomena is attempted. The presentation is elementary in character, starting with the simple geometry of the spin, then…

Abstract

In this paper a comprehensive survey of spinning phenomena is attempted. The presentation is elementary in character, starting with the simple geometry of the spin, then dealing with autorotation, including wing‐dropping tendencies, passing on then to a consideration of aerodynamic pitching and yawing moments, and finally some attention is given in turn to the incipient spin, the steady spin and recovery. The arguments are in the main qualitative so that a student of the subject may first familiarise himself with the fundamental principles. A bibliography is given which includes all the important papers published on the subject within the last few years, together with a few which are now more of historical interest. Most of these reports emanate from the A.R.C. and N.A.C.A. and due acknowledgment is made of the source of some of the experiments which have been taken in illustration of the points made. Although not the urgent problem that it once was, the subject of the spinning of aeroplanes continues to occupy a prominent place in the programmes of various research establishments, both here and abroad. Because both of the complexity of the phenomena involved and of the great importance that an ultimate solution should be found it has continued to be since the war one of the most difficult and protracted problems in aeronautics. Owing to the body of experimental data which has been gradually built up, model and full scale, designers now know what peculiar properties in an aeroplane are liable to prove dangerous as far as recovery is concerned. There is unfortunately no mathematical precision about this process and the fact that machines can still be built which, unless they are tested in the spinning tunnel and the necessary modifications made, might become uncontrollable in a spin should be sufficient to indicate that a final solution is far front having been achieved. It seems exceedingly unlikely that there will ever be sufficient experimental evidence to enable a designer to predict confidently that his machine, if it be perfectly orthodox, will not have some vicious spinning tendency. On the other hand, any designer could build a perfectly safe aeroplane from the point of view of spinning if due regard had not to be paid to other items of performance and safety. The necessity for compromise in design becomes a major problem when spinning is one of the factors that have to be taken into account. There is ample evidence that this problem is being resolutely tackled by designers. All the same, the present position cannot be regarded as satisfactory and, unless some new device is produced which will remove autorotation from the possible regimes of an aeroplane, we must continue to progress along already well‐tried lines.

Details

Aircraft Engineering and Aerospace Technology, vol. 11 no. 2
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article
Publication date: 6 July 2010

Tiauw Hiong Go and Wang Hao

With possible practical application in a micro aerial vehicle (MAV), propulsion characteristics of a flapping wing with modified pitch motion are investigated both…

Abstract

Purpose

With possible practical application in a micro aerial vehicle (MAV), propulsion characteristics of a flapping wing with modified pitch motion are investigated both theoretically and experimentally in this paper.

Design/methodology/approach

Modified pitch motion is defined as a sinusoidal pitch motion with the pitch axis outside the wing chord line. Based on the momentum theory, an analytical model is developed to analyze the propulsion characteristics of the defined flapping wing. Following that, a water tunnel study of the effects of pitch axis distance, pitch frequency, and stream velocity on thrust generation is carried out. Thrust is directly measured using a 1‐D load cell and the flow visualization is captured using a high speed video camera.

Findings

It is found that shifting pitch axis outside wing chord line benefits the thrust generation significantly. Positive average thrust is produced at a relatively low frequency and increases almost quadratically with the motion frequency. The effect of stream velocity on the thrust time history is signified but has little effect on the average thrust magnitude.

Practical implications

Compared to other types of flapping wing motions, the proposed flapping can be achieved with simple mechanism and thus has the edge in practicality for propelling MAV or other submarine systems.

Originality/value

The paper provides useful aerodynamic characteristics of a type of flapping wing motion which possesses mechanical simplicity and relatively large thrust generation at low‐flapping frequency. This flapping wing has the potential to provide propulsion for a MAV or other submarine systems.

Details

Aircraft Engineering and Aerospace Technology, vol. 82 no. 4
Type: Research Article
ISSN: 0002-2667

Keywords

To view the access options for this content please click here
Article
Publication date: 1 April 2001

Yuan Su and Yihua Cao

Studies of the hingeless rotor helicopter dynamic stability and control laws are conducted. A new method is given for the calculation of stability and controllability of a…

Abstract

Studies of the hingeless rotor helicopter dynamic stability and control laws are conducted. A new method is given for the calculation of stability and controllability of a helicopter in flight condition with lateral velocity. First, the rotary wing dynamic model considered is the one of flap‐pitch (including the elastic deformation of control system) – torsion coupling. The induced velocity non‐uniform distribution derived from vortex theory is taken into account. Then, according to the established motion model of the helicopter, the effects of induced velocity distribution, flap‐pitch‐torsion coupling and lateral velocity on the stability and controllability of the helicopter are analyzed. Based on the analyses of dynamic stability of the helicopter, the unstable mode and the necessity of installation of stability augmentation system (SAS) are recognized. Finally, the control laws of SAS for helicopter pitching, rolling and yawing motions are presented. After establishing helicopter flight control state equations, the performance analyses and step response simulation for helicopter SAS are carried out.

Details

Aircraft Engineering and Aerospace Technology, vol. 73 no. 2
Type: Research Article
ISSN: 0002-2667

Keywords

1 – 10 of over 2000