The Relationship between Flow Field and Unsteady Fluid Forces Acting on a Flat Plate

2020 ◽  
Vol 2020 (0) ◽  
pp. OS03-08
Author(s):  
Yoshinobu KIKUCHI ◽  
Naoto KATO ◽  
Hiroaki HASEGAWA
Keyword(s):  
Flow Field ◽  
Flat Plate ◽  
Fluid Forces ◽  
Unsteady Fluid ◽  
The Relationship

Characteristics of Dynamic Forces Generated by a Flapping Butterfly and its Wake Structure

2017 ◽  
Author(s):  
Masaki Fuchiwaki ◽  
Kazuhiro Tanaka
Keyword(s):  
Flow Field ◽  
Butterfly Wing ◽  
Vortex Loop ◽  
Insect Wing ◽  
Fluid Forces ◽  
Insect Wings ◽  
Piv Measurement ◽  
Dynamic Forces ◽  
Butterfly Wings ◽  
The Relationship

A typical example of the flow field around a moving elastic body is that around butterfly wings. Butterflies fly by skillfully controlling this flow field, and vortices are generated around their bodies. The motion of their elastic wings produces dynamic fluid forces by manipulating the flow field. For this reason, there has been increased academic interest in the flow field and dynamic fluid forces produced by butterfly wings. A number of recent studies have qualitatively and quantitatively examined the flow field around insect wings. In some such previous studies, the vortex ring or vortex loop formed on the wing was visualized. However, the characteristics of dynamic forces generated by the flapping insect wing are not yet sufficiently understood. The purpose of the present study is to investigate the characteristics of dynamic lift and thrust produced by the flapping butterfly wing and the relationship between the dynamic lift and thrust and the flow field around the butterfly. We conducted the dynamic lift and thrust measurements of a fixed flapping butterfly, Idea leuconoe, using a six-axes sensor. Moreover, two-dimensional PIV measurement was conducted in the wake of the butterfly. The butterfly produced dynamic lift in downward flapping which became maximum at a flapping angle of approximately 0.0 deg. At the same time, the butterfly produced negative dynamic thrust during downward flapping. The negative dynamic thrust was not produced hydrodynamically by a flapping butterfly wing because a jet was not formed in front of the butterfly. The negative dynamic thrust was the kicking force for jumping and the maximum of this kicking force was about 6.0 times as large as the weight. On the other hand, the butterfly produced dynamic thrust in upward flapping which was approximately 6.0 times as large as the weight of the butterfly. However, the attacking force by the abdomen of the butterfly was included in the dynamic thrust and we have not yet clarified quantitatively the dynamic thrust produced by the butterfly wing.

Dynamic Forces Acting on Elastic Heaving Airfoils Based on the Bending Stiffness Considerations

2014 ◽  
Author(s):  
Masaki Fuchiwaki ◽  
Tetsushi Nagata ◽  
Kazuhiro Tanaka
Keyword(s):  
Flow Field ◽  
Elastic Deformation ◽  
Vortex Flow ◽  
Moving Boundary ◽  
Bending Stiffness ◽  
Fluid Forces ◽  
Dynamic Forces ◽  
Flow Phenomena ◽  
The Impact ◽  
The Relationship

In recent years the flow field in the vicinity of moving airfoils capable of flexible elastic deformation has become a focus of attention, and its effects are beginning to be understood. Flow in the vicinity of an elastically deforming airfoil may be understood as a fluid-structure interaction (FSI) problem, and the motion and deformation of elastic airfoils, as well as the associated vortex flow phenomena in their vicinity, are complicated. Especially, the shape and hardness of the elastic regions of an airfoil may affect its rigidity and its bending characteristics and for this reason the influence of such airfoils on the flow fields around them require more detailed consideration. In this study, we fix the bending stiffness, which uniquely determines the nature of the elastic deformation of an elastic airfoil, and study the impact of changes in this quantity on the flow field, as well as the parameters that govern the fluid forces acting on the airfoil. In particular, our goal is to clarify the relationship between three key parameters, Strouhal number St, Reynolds number Re and bending stiffness K and is to elucidate the nature of the dynamic forces acting on an elastic airfoil as a function of these three dimensionless parameters. The bending stiffness K of the elastic airfoil is an important parameter that determines the bending characteristics and the moving boundary conditions at the wall surfaces in the fluid. By defining the new quantity St2/K, we showed that the characteristic of dynamic forces depends on the ratio St2/K.

Suppression of Fluid Forces Acting on a Square Prism by Passive Control

1997 ◽  
Vol 119 (3) ◽  
pp. 506-511 ◽  
Author(s):  
H. Sakamoto ◽  
K. Tan ◽  
N. Takeuchi ◽  
H. Haniu
Keyword(s):  
Flat Plate ◽  
Vortex Shedding ◽  
Passive Control ◽  
Fluid Forces ◽  
Maximum Reduction ◽  
Square Prism ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Unsteady Fluid ◽  
Lift And Drag

Suppression of fluid forces acting on a square prism by passive control of the approaching flow was investigated in the present study. Flow was controlled using a small flat plate upstream of the prism. The position of the flat plate was varied within the range of S/W = 0 ~ 3.0 (S: distance between the flat plate and square prism, W: width of square prism) and the width h of the flat plate ranged from 2 mm to 8 mm (h/W = 0.05 ~ 0.19). Steady and unsteady fluid forces, vortex shedding frequency, and flow pattern were systematically investigated. The maximum reduction of time-averaged drag was 75 percent, and the maximum reduction in fluctuating lift and drag was 95 and 80 percent, respectively, using a flat plate 1/10 of the size of the square prism.

The Unsteady Fluid Flow Due to Corona Discharge in a System of Wire and Plate Electrodes

2002 ◽  
Author(s):  
Yusuke Imai ◽  
Yoshiaki Itoh ◽  
Hideyuki Mihira ◽  
Masatsugu Yoshizawa
Keyword(s):  
Flow Field ◽  
Corona Discharge ◽  
Point Of View ◽  
Laser Doppler Velocimeter ◽  
Physical Point ◽  
Fluid Force ◽  
Fluid Forces ◽  
Unsteady Fluid Flow ◽  
The Wire ◽  
Unsteady Fluid

Lateral oscillation of a wire electrode occurs when high dc voltage is applied between a wire and plate electrodes in an electrostatic field with corona discharge. The feature is that the horizontal component of the wire oscillation gradually increases and is excited with the fundamental natural frequency of the wire oscillation. We have already discussed the effects of the electrostatic and the fluid forces on the wire oscillation from the physical point of view. The fluid force on the wire due to corona wind was assumed to be one of main reasons for the outbreak mechanism of the wire oscillation. However, the outbreak mechanism of the wire oscillation has not been given yet. The main purpose of this paper is to examine another possible reason for the outbreak mechanism of the wire oscillation due to the fluid force. Some experiments are made to investigate whether oscillation of a non-conductive string, placed in the flow field, is excited by the fluid force or not. Moreover, the PIV (Particle Image Velocimetry) and the LDV (Laser Doppler Velocimeter) techniques are used to measure the flow field to confirm the hypothesis of the outbreak mechanism t hat the wire oscillation is excited due to the fluctuation of the fluid force on the wire.

The Effect of Flow Coefficient on the Self Noise Generated by a Ducted Rotor

2008 ◽  
Author(s):  
David B. Stephens ◽  
Scott C. Morris ◽  
William K. Blake
Keyword(s):  
Flow Field ◽  
The Self ◽  
Flow Coefficient ◽  
Hot Wire ◽  
Fluid Forces ◽  
Inflow Turbulence ◽  
Order Change ◽  
Ducted Rotor ◽  
Unsteady Fluid ◽  
Rigid Surfaces

Sound generation in low Mach number turbomachines is typically dominated by unsteady fluid forces on rigid surfaces. As a result, the radiated sound is closely related to the unsteady flow field. The present study focused on the self noise that is generated by a ducted rotor separate from the effect of noise due to inflow turbulence. The flow rate through the rotor was independently varied in order change the mean lift on the blades. Measurements of the flow field around a ducted rotor were found to provide insight to the various mechanisms of sound that are present at different mean loading conditions. At lower flow rates the blades were partially stalled, resulting in significantly increased noise levels. The measurements included rotor wake measurements using hot-wire anemometry and far field sound. A simple model to predict the radiated self noise based on the hot-wire measurements is presented.

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