The effect of dynamic twisting on the flow field and the unsteady forces of a heaving flat plate

Abstract

Many marine animals can dynamically twist their pectoral fins while swimming. The effects of such dynamic twisting on the unsteady forces on the fin and its surrounding flow field are yet to be understood in detail. In this paper, a flat plate executing a heaving maneuver is subjected to a similar dynamic twisting. In particular, the effects of the direction of twist, non-dimensional heaving amplitude, and reduced frequency are studied using a force sensor and Particle Image Velocimetry (PIV) measurements. Two reduced frequencies, Γ = 0.105, and 0.209, and two twisting modes are investigated. In the first twisting mode, the plate is twisted in the direction of the heave (forward-twist), and in the second mode, the plate is twisted opposite to the direction of the heave (backward-twist). Force sensor measurements show that the forward-twist recovers some of the lift that is usually lost during the upstroke of flapping locomotion. Additionally, the forward-twist maintains a near-constant lift coefficient during the transition between downstroke and upstroke, suggesting a more stable form of locomotion. PIV results show that forward-twist limits circulation and leading-edge vortex (LEV) growth during the downstroke, keeping ΓΓ ≈ 0 at the cost of the reduced lift. By contrast, backward-twist increases the circulation during the downstroke, resulting in large increases in both lift and drag coefficients. Force sensor data also showed that this effect on the lift is reversed during the upstroke, where the backward-twist causes a negative lift. The effects of each twisting mode are mainly caused by the changes in the shear layer velocity that occur as a result of spanwise twisting.

A numerical study on the aerodynamic effects of dynamic twisting on forward flight flapping wings

“…This highlights the trade-off between efficiency and force generation in the context of wing twist. Recently, Soto and Bhattacharya [25] conducted an experimental study that specifically investigated a flat plate executing a heaving motion. The main objective of their study was to examine how active and dynamic twisting of the plate affected its aerodynamic performance.…”

A Study on Influence of Flapping Dynamic Characteristics on Vibration Control of Active Rotor with Trailing-Edge Flaps

“…Additionally, the dynamic twist technique has other applications. A series of studies on the effect of dynamic twisting on the flow field and the unsteady forces were conducted by Bhattacharya et al [7][8][9]. However, the active twist rotor has not been used in engineering applications due to the limitations in drive technology.…”