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Article
Publication date: 5 October 2015

Zhiyi Yu, Baoshan Zhu and Shuliang Cao

Interphase forces between the gas and liquid phases determine many phenomena in bubbly flow. For the interphase forces in a multiphase rotodynamic pump, the magnitude…

Abstract

Purpose

Interphase forces between the gas and liquid phases determine many phenomena in bubbly flow. For the interphase forces in a multiphase rotodynamic pump, the magnitude analysis was carried out within the framework of two-fluid model. The purpose of this paper is to clarify the relative importance of various interphase forces on the mixed transport process, and the findings herein will be a base for the future study on the mechanism of the gas blockage phenomenon, which is the most challenging issue for such pumps.

Design/methodology/approach

Four types of interphase forces, i.e. drag force, lift force, virtual mass force and turbulent dispersion force (TDF) were taken into account. By comparing with the experiment in the respect of the head performance, the effectiveness of the numerical model was validated. In conditions of different inlet gas void fractions, bubble diameters and rotational speeds, the magnitude analyses were made for the interphase forces.

Findings

The results demonstrate that the TDF can be neglected in the running of the multiphase rotodynamic pump; the drag force is dominant in the impeller region and the outlet extended region. The sensitivity analyses of the bubble diameter and the rotational speed were also performed. It is found that larger bubble size is accompanied by smaller predicted drag but larger predicted lift and virtual mass, while the increase of the rotational speed can raise all the interphase forces mentioned above.

Originality/value

This paper has revealed the magnitude information and the relative importance of the interphase forces in a multiphase rotodynamic pump.

Details

Engineering Computations, vol. 32 no. 7
Type: Research Article
ISSN: 0264-4401

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Article
Publication date: 1 June 1955

P.R. Payne

In‐plane vibration of a balanced helicopter rotor is caused by variations with azimuth of the in‐plane forces acting on individual blades. These forces may be summarized…

Abstract

In‐plane vibration of a balanced helicopter rotor is caused by variations with azimuth of the in‐plane forces acting on individual blades. These forces may be summarized under three headings: ‘Induced forces’ caused by the inclination of elemental lift vectors relative to the axis of rotation. ‘Profile drag forces’: variations are caused by changes with azimuth angle of the angle and airspeed of the individual blade elements. ‘Coriolis forces’, which are caused by blade flapping, which brings about a variation of blade moment of inertia about the axis of rotation. Equations are developed in this paper for the resultant hub force due to each of these forces, on the assumptions of small flapping hinge offset. It is assumed that blades are linearly twisted and tapered, an assumption which in practice can be applied to any normal rotor. It is shown that by suitably inclining the mechanical axis it is possible to balance out the worst induced and profile drag vibrations by the coriolis one, which can be made to have opposite sign. If the mechanical axis is fixed in the fuselage, this suppression is fully effective for one flight condition only. In multi‐rotor helicopters, vibration suppression can be extended over a much wider range by varying the fuselage attitude. The logical result of this analysis is, for single rotor helicopters, a floating mechanical axis which can be adjusted or trimmed by the pilot. This would be quite simple to do on a tip‐driven rotor, and has already been achieved with a mechanical drive on the Doman helicopter. The more important causes of vibration from an unbalanced rotor are next con‐sidered, attention here being confined principally to fully articulated rotors, which are the most difficult to balance because the drag hinges tend to magnify all in‐accuracies in finish and balance. From a brief discussion of the vertical vibration of an imperfect rotor it is shown that some contemporary methods of ‘tracking’ are fundamentally wrong. Finally the vibration due to tip‐mounted power units is described. In discussing the effect of a vibratory force on a helicopter a simple response chart is developed, and it is thought that its use could well be accepted as a simple standard for general assessment purposes. In the development of equations for vibration the following points of general technical interest are put forward: An equation for induced torque is developed which includes a number of hitherto neglected parameters. A new form of equation for mean lift coefficient of a blade is suggested. The simple Hafner criterion for flight envelopes is shown to give rise to considerable error, and the use of Eq. (28) is suggested in its place. The variation of profile torque with forward speed is given, and the increase due to ? varying round the disk is expressed as an explicit equation, thus allowing considerable improvement in the present methods of allowing for this effect.

Details

Aircraft Engineering and Aerospace Technology, vol. 27 no. 6
Type: Research Article
ISSN: 0002-2667

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Article
Publication date: 4 September 2018

Ehsan Adeeb, Basharat Ali Haider and Chang Hyun Sohn

The purpose of this study is to numerically investigate the influence of corner radius on the flow around two square cylinders in tandem arrangements at a Reynolds number of 100.

Abstract

Purpose

The purpose of this study is to numerically investigate the influence of corner radius on the flow around two square cylinders in tandem arrangements at a Reynolds number of 100.

Design/methodology/approach

Six models of square cylinders with corner radii R/D = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5 (where R denotes the corner radius and D denotes the characteristic dimension of the body) were studied using an immersed boundary-lattice Boltzmann method, and the results were compared with those obtained using a two-dimensional unsteady finite volume method. The cylinders were mounted in a tandem configuration (1.5 ≤ L/D ≤ 10 where L denotes the in-line separation between the cylinder centers). The simulated models were quantitatively compared to the aerodynamic force coefficients and Strouhal number. Furthermore, qualitative analysis is presented in the form of flow streamlines and vorticity contours.

Findings

The R/D and L/D values were varied to observe the variation in the flow characteristics in the gap and wake regions. The numerical results revealed two different regimes over the spacing range. The drag force on the downstream cylinder was negative for all corner radii values when the cylinders were placed at L/D = 3.0 (a single-body system). Subsequently, a sudden increase was observed in the aerodynamic forces (drag and lift) when L/D increased. A different gap value was identified in the transformation from a single-body to a two-body system for different corner radii. To verify the single-body system, a simulation was carried out with a single cylinder having a longitudinal geometric dimension equal to the tandem arrangement (L/D + D). Furthermore, in a single-body regime, the total drag of a tandem cylinder was less than that of a single cylinder, thus demonstrating the benefits of using tandem structures. A significant reduction in the aerodynamic forces and drag force was achieved by rounding the sharp corners and placing the cylinders in close proximity. An appropriate configuration of the tandem cylinders with a rounded corner of R/D = 0.4 and 0.5 at L/D = 3.0 and the range is enhanced to L/D = 4.0 for 0.0 ≤ R/D < 0.4 to achieve adequate drag reduction.

Originality/value

To the best of the author’s knowledge, there is a paucity of studies examining the effect of corner radius on bluff bodies arranged in a tandem configuration.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 28 no. 7
Type: Research Article
ISSN: 0961-5539

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Article
Publication date: 15 October 2018

Ming Liu, Shan Cao and Shuliang Cao

The modeling of interphase forces plays a significant role in the numerical simulation of gas–liquid flow in a rotodynamic multiphase pump, which deserves detailed study.

Abstract

Purpose

The modeling of interphase forces plays a significant role in the numerical simulation of gas–liquid flow in a rotodynamic multiphase pump, which deserves detailed study.

Design/methodology/approach

Numerical analysis is conducted to estimate the influence of interphase forces, including drag force, lift force, virtual mass force, wall lubrication force and turbulent dispersion force.

Findings

The results show that the magnitude of the interphase forces can be sorted by: drag force > virtual mass force > lift force > turbulent dispersion force > wall lubrication force. The relations between interphase forces and velocity difference of gas–liquid flow and also the interphase forces and gas volume fraction are revealed. The distribution characteristics of interphase forces in the passages from impeller inlet to diffuser outlet are illustrated and analyzed. According to the results, apart from the drag force, the virtual mass force, lift force and turbulent dispersion force are required, whereas wall lubrication force can be neglected for numerical simulation of gas–liquid flow in a rotodynamic multiphase pump. Compared with the conventional numerical method which considers drag force only, the relative errors of predicted pressure rise and efficiency based on the proposed numerical method in account of four major forces can be reduced by 4.95 per cent and 3.00 per cent, respectively.

Originality value

The numerical analysis reveals the magnitude and distribution of interphase forces inside multiphase pump, which is meaningful for the simulation and design of multiphase pump.

Details

Engineering Computations, vol. 35 no. 6
Type: Research Article
ISSN: 0264-4401

Keywords

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Article
Publication date: 29 December 2017

Siamak Nazemi, Ramin Khajavi, Hamidreza Rabie Far, Mohammad Esmail Yazdanshenas and Manouchehr Raad

During 2008 Olympics, Michael Phelps had a record-breaking performance. One contributing factor to his success was the full-body swimsuit he was wearing. Cases like these…

Abstract

Purpose

During 2008 Olympics, Michael Phelps had a record-breaking performance. One contributing factor to his success was the full-body swimsuit he was wearing. Cases like these were the reason for the initiation of study and research for improvement in the new generation of sport gears. The purpose of this paper is to show that drag force plays a significant role in swimmers’ speed through the water; thus, using swimsuit with minimized drag force becomes imperative for Olympians like Michael Phelps.

Design/methodology/approach

This paper shows a comparative evaluation of hydrodynamics of three PET fabrics with different finishings that have hydrophobic behavior over a range of Reynolds number 1.0218×103 and 1.365×103 in the air medium at 20°C ambient temperature, and Reynolds number ranging from 15.68856×103 to 20.958×103 in the water medium at 20°C ambient temperature under stable stretch conditions.

Findings

The results show that hydrophobic finishing reduces the drag force by 1.5 percent at the angles of attack of 0 and 90 degrees.

Originality/value

If all the factors are considered to be stable for the swimmer, the drag force reduces by 1.5 percent, thereby increasing the speed of swimmer by 1.22 percent, which means that the record of the swimmer improves by 0.819 seconds.

Details

International Journal of Clothing Science and Technology, vol. 30 no. 1
Type: Research Article
ISSN: 0955-6222

Keywords

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Article
Publication date: 2 October 2017

M. Tahani, M. Masdari and M. Kazemi

This paper aims to analyze the influence of the changings in geometrical parameters on the aerodynamic performance of the control canard projectiles.

Abstract

Purpose

This paper aims to analyze the influence of the changings in geometrical parameters on the aerodynamic performance of the control canard projectiles.

Design/methodology/approach

Because of the mentioned point, the range of projectiles increment has a considerable importance, and the design algorithm of a control canard projectile was first written. Then, were studied the effects of canard geometric parameters such as aspect ratio, taper ratio and deflectable nose on lift to drag coefficient ratio, static margin based on the slender body theory and cross section flow.

Findings

The code results show that aspect ratio increment, results in an increase in lift-to-drag ratio of the missile, but increase in canard taper ratio results in increasing of lift-to-drag ratio at 1° angle of attack, while during increasing the canard taper ratio up to 0.67 at 4° angle of attack, lift to drag first reaches to maximum and then decreases. Also, static margin decreases with canard taper ratio and aspect ratio increment. The developed results for this type of missile were compared with same experimental and computational fluid dynamic (CFD) results and appreciated agreement with other results at angles of attack between 0° and 6°.

Practical implications

To design a control canard missile, the effect of each geometric parameter of canard needs to be estimated. For this purpose, the suitable algorithm is used. In this paper, the effects of canard geometric parameters, such as aspect ratio, taper ratio and deflectable nose on lift-to-drag coefficient ratio and static margin, were studied with help of the slender body theory and cross-section flow.

Originality/value

The contribution of this paper is to predict the aerodynamic characteristics for the control canard missile. In this study, the effect of the design parameter on aerodynamic characteristics can be estimated, and the effect of geometrical characteristics has been analyzed with a suitable algorithm. Also, the best lift-to-drag coefficient for the NASA Tandem Control Missile at Mach 1.75 was selected at various angles of attack. The developed results for this type of missile were compared with same experimental and CFD results.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 6
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 5 June 2020

Mustafa Kaya and Munir Ali Elfarra

The critical Mach number, lift-to-drag ratio and drag force play important role in the performance of the wings. This paper aims to investigate the effect of taper…

Abstract

Purpose

The critical Mach number, lift-to-drag ratio and drag force play important role in the performance of the wings. This paper aims to investigate the effect of taper stacking, which has been used to generalize wing sweeping, on those parameters.

Design/methodology/approach

The results obtained are based on steady-state turbulent flowfields computations. The baseline wing is ONERA M6. Various wing planforms are generated by linearly or parabolically varying the spanwise stacking location. The critical Mach number is determined by changing the freestream Mach number for a fixed angle of attack. On the other hand, the analysis of the drag force is carried out by changing the angle of attack to keep the lift force constant.

Findings

By changing the stacking location, the critical Mach number and the corresponding lift-to-drag ratio have increased by around 7 and 3%, respectively. A reduction of 12.8% in total drag force has been observed in one of the analyzed cases. Moreover, there exist some cases in which the values of drag reduce significantly while the lift is the same.

Practical implications

The results of this new stacking approach have implied that the drag force can be decreased without decreasing the lift. This outcome is valuable for increasing the range and endurance of an aircraft.

Originality/value

This work generalizes wing sweeping by modifying the taper stacking along the span. In literature, wing sweep is enhanced using segmented stacking of taper distribution. The present study is further enhancing this concept by introducing continuous stacking (infinite number of stacking segments) for the first time.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 7
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 3 January 2017

Xiaowei Shao, Mingxuan Song, Jihe Wang, Dexin Zhang and Junli Chen

The purpose of this paper is to present a method to achieve small satellite formation keeping operations by using the differential lift and drag to control the drift…

Abstract

Purpose

The purpose of this paper is to present a method to achieve small satellite formation keeping operations by using the differential lift and drag to control the drift caused by J2 perturbation in circular or near-circular low earth orbits (LEOs).

Design/methodology/approach

Each spacecraft is equipped with five large flat plates, which can be controlled to generate differential accelerations. The aerodynamic lift and drag acting on a flat plate is calculated by the kinetic theory. To maintain the formation within tracking error bounds in the presence of J2 perturbation, a nonlinear Lyapunov-based feedback control law is designed.

Findings

Simulation results demonstrate that the proposed method is efficient for the satellite formation keeping and better accuracy advantage in comparison with classical approaches via the fixed maximum differential aerodynamic acceleration.

Research limitations/implications

Because the aerodynamic force will reduce drastically as the orbital altitude increases, the formation keeping control strategy for small satellites presented in this paper should be limited to the scenarios when satellites are in LEO.

Practical implications

The formation keeping control method in this paper can be applied to solve satellite formation keeping problem for small satellites in LEO.

Originality/value

This paper proposes a Lyapunov control strategy for satellite formation keeping considering both lift and drag forces, and simulation results show better performance with high accuracy under J2 perturbation.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 1
Type: Research Article
ISSN: 1748-8842

Keywords

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Article
Publication date: 10 July 2019

Zhen Chen, Zhenqqi Gu and Tao Jiang

The main purpose of this paper is to gain a better understanding of the transient aerodynamic characteristics of moving windshield wipers. In addition, this paper also…

Abstract

Purpose

The main purpose of this paper is to gain a better understanding of the transient aerodynamic characteristics of moving windshield wipers. In addition, this paper also strives to illustrate and clarify how the wiper motion impacts the airflow structure; the aerodynamic interaction of two wipers is also discussed.

Design/methodology/approach

A standard vehicle model proposed by the Motor Industry Research Association and a pair of simplified bone wipers are introduced, and a dynamic mesh technique and user-defined functions are used to achieve the wiper motion. Finite volume methods and large eddy simulation (LES) are used to simulate the transient airflow field. The simulation results are validated through the wind tunnel test.

Findings

The results obtained from the study are presented graphically, and pressure, velocity distributions, airflow structures, aerodynamic drag and lift force are shown. Significant influences of wiper motion on airflow structures are achieved. The maximum value of aerodynamic lift and drag force exists when wipers are rotating and there is a certain change rule. The aerodynamic lift and drag force when wipers are rotating downward is greater than when wipers are rotating upward, and the force when rotating upward is greater than that when steady. The aerodynamic lift and drag forces of the driver-side wiper is greater than those of the passenger-side wiper.

Originality/value

The LES method in combination with dynamic mesh technique to study the transient aerodynamic characteristics of windshield wipers is relatively new.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

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Article
Publication date: 28 May 2021

M.R. Saber and M.H. Djavareshkian

In the present research, the effect of the flexible shells method in unsteady viscous flow around airfoil has been studied. In the presented algorithm, due to the…

Abstract

Purpose

In the present research, the effect of the flexible shells method in unsteady viscous flow around airfoil has been studied. In the presented algorithm, due to the interaction of the aerodynamic forces and the structural stiffness (fluid-structural interaction), a geometrical deformation as the bump is created in the area where the shock occurs. This bump causes instead of compressive waves, a series of expansion waves that produce less drag and also improve the aerodynamic performance to be formed. The purpose of this paper is to reduce wave drag throughout the flight range. By using this method, we can be more effective than recent methods throughout the flight because if there is a shock, a bump will form in that area, and if the shock does not occur, the shape of the airfoil will not change.

Design/methodology/approach

In this simulation pressure-based procedure to solve the Navier-Stokes equation with collocated finite volume formulation has been developed. For this purpose, a high-resolution scheme for fluid and structure simulation in transonic flows with an arbitrary Lagrangian-Eulerian method is considered. To simulate Navier-Stokes equations large eddy simulation model for compressible flow is used.

Findings

A new concept has been defined to reduce the transonic flow drag. To reduce drag force and increase the performance of airfoil in transonic flow, the shell can be considered flexible in the area of shock on the airfoil surface. This method refers to the use of smart materials in the aircraft wing shell.

Originality/value

The value of the paper is to develop a new approach to improve the aerodynamic performance and reduce drag force and the efficiency of the method throughout the flight. It is noticeable that the new algorithm can detect the shock region automatically; this point was disregarded in the previous studies. It is hoped that this research will open a door to significantly enhance transonic airfoil performance.

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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