Vortex Flow Behind a Heaving Elastic Flat Plate

2008 ◽  
Author(s):  
Masaki Fuchiwaki ◽  
Kazuhiro Tanaka
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
Vortex Flow ◽  
Low Reynolds Number ◽  
Vertical Direction ◽  
Vortex Street ◽  
Wake Flow ◽  
Piv Measurement ◽  
Low Reynolds ◽  
Accelerating Flow

An unsteady flow in a low Reynolds number region attracts attention in recent years. Various experiments/numerical analyses have been conducted in wake flow fields of objects with unsteady motions in low Reynolds number regions have been studied and reported recently. The authors clarified vortical structures in a wake of a rigid airfoil (NACA0010) with pitching, heaving and an unsteady motion with these motions combined quantitatively. The purpose of this study is to evaluate quantitatively the vortex flow formed in the wake of a flat airfoil whose edge deforms elastically by a PIV measurement by giving a heaving motion to the flat plate in a low Reynolds number region. A clear thrust producing vortex street equivalent to the airfoil shape can be formed by giving elasticity to the latter part of a rigid flat airfoil. vortices forming the thrust producing vortex street is extremely large and their vorticity is equivalent to that of NACA0010. In the mainstream of a vortex street forming a propulsion power generating vortex street, the vortex interval in the vertical direction is comparatively large and an interference of the vortices rolling up from the pressure and suction sides is small therefore the accelerating flow induced by these vortices becomes as large as the mainstream. The dynamic thrust acting on the elastic flat plate is greater than that of NACA0010. Because vortices with high vorticity roll up and these vortices are aligned with a comparatively large vortex interval in the vertical direction therefore a large accelerating flow is induced in the wake.

Characteristics of Dynamic Thrust on an Unsteady Airfoil in Pitching and Heaving Motions

2007 ◽  
Author(s):  
Masaki Fuchiwaki ◽  
Kazuhiro Tanaka ◽  
Masahiro Nakashima
Keyword(s):  
Reynolds Number ◽  
Vortex Flow ◽  
Low Reynolds Number ◽  
Flow Structures ◽  
Piv Measurement ◽  
Vortex Streets ◽  
Dynamic Forces ◽  
Thrust Efficiency ◽  
Low Reynolds ◽  
Maximum Thrust

The unsteady flow at low Reynolds number regions has been attracted significant attentions in recent years. However, detailed vortex flow structures and characteristics of dynamic forces acting on an unsteady airfoil at a low Reynolds number region have not been clarified sufficiently. In this study, the detailed vortex flow structures behind an unsteady airfoil in pitching and heaving motions at low Reynolds number regions have been measured by PIV measurement. Moreover, the dynamic thrust measurements on an airfoil have been performed by a six-axes sensor in a water tunnel. An unsteady airfoil in pitching and heaving motions forms thrust producing vortex streets with vortices accompanied with large vorticities, without disturbing flow around an airfoil, comparing to airfoils with independent pitching and heaving motions. In the wake of an unsteady airfoil in pitching and heaving motions, jet flow is generated at φ = π/3, π/2, π and 3π/2. In particular, jet velocity becomes over 2.0 at φ = π/3 and π and the values are greater than those of the heaving airfoil. For φ = π/3 and π/2, large dynamic thrusts are produced. The thrust efficiency increases drastically with increase of Strouhal numbers and reaches its maximum value at around St = 0.2, then decreases gradually. At φ = π/3, 2π/3, 5π/6, π, 7π/6 and 4π/3, significantly large thrusts are produced on an unsteady airfoil however at the same time large lifts and moments are generated therefore thrust efficiency becomes small. The maximum thrust efficiency is φ = π/2 and is approximately 0.40.

Vortex Shedding Analysis in the Wake of a Flat Plate at Low Incidence and Low Reynolds Number

2021 ◽  
Author(s):  
Bastav Borah ◽  
Anand Verma ◽  
Vinayak Kulkarni ◽  
Ujjwal K. Saha
Keyword(s):  
Reynolds Number ◽  
Velocity Field ◽  
Flat Plate ◽  
Vortex Shedding ◽  
Low Reynolds Number ◽  
General Tendency ◽  
Flat Plates ◽  
Trailing Edge ◽  
Low Reynolds ◽  
Low Incidence

Abstract Vortex shedding phenomenon leads to a number of different features such as flow induced vibrations, fluid mixing, heat transfer and noise generation. With respect to aerodynamic application, the intensity of vortex shedding and the size of vortices play an essential role in the generation of lift and drag forces on an airfoil. The flat plates are known to have a better lift-to-drag ratio than conventional airfoils at low Reynolds number (Re). A better understanding of the shedding behavior will help aerodynamicists to implement flat plates at low Re specific applications such as fixed-wing micro air vehicle (MAV). In the present study, the shedding of vortices in the wake of a flat plate at low incidence has been studied experimentally in a low-speed subsonic wind tunnel at a Re of 5 × 104. The velocity field in the wake of the plate is measured using a hot wire anemometer. These measurements are taken at specific points in the wake across the flow direction and above the suction side of the flat plate. The velocity field is found to oscillate with one dominant frequency of fluctuation. The Strouhal number (St), calculated from this frequency, is computed for different angles of attack (AoA). The shedding frequency of vortices from the trailing edge of the flat plate has a general tendency to increase with AoA. In this paper, the generation and subsequent shedding of leading edge and trailing edge vortices in the wake of a flat plate are discussed.

On High-Performance Airfoil at Very Low Reynolds Number

2016 ◽  
Vol 28 (3) ◽  
pp. 273-285
Author(s):  
Katsuya Hirata ◽  
◽  
Ryo Nozawa ◽  
Shogo Kondo ◽  
Kazuki Onishi ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
High Performance ◽  
Low Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Slow Flow ◽  
Low Reynolds Numbers ◽  
Low Reynolds

[abstFig src='/00280003/02.jpg' width=""300"" text='Iso-Q surfaces of very-slow flow past an iNACA0015' ] The airfoil is often used as the elemental device for flying/swimming robots, determining its basic performances. However, most of the aerodynamic characteristics of the airfoil have been investigated at Reynolds numbers Re’s more than 106. On the other hand, our knowledge is not enough in low Reynolds-number ranges, in spite of the recent miniaturisation of robots. In the present study, referring to our previous findings (Hirata et al., 2011), we numerically examine three kinds of high-performance airfoils proposed for very-low Reynolds numbers; namely, an iNACA0015 (the NACA0015 placed back to front), an FPBi (a flat plate blended with iNACA0015 as its upper half) and an FPBN (a flat plate blended with the NACA0015 as its upper half), in comparison with such basic airfoils as a NACA0015 and an FP (a flat plate), at a Reynolds number Re = 1.0 × 102 using two- and three-dimensional computations. As a result, the FPBi shows the best performance among the five kinds of airfoils.

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