# Unsteady High-Lift Mechanisms from Heaving Flat Plate Simulations

## TL;DR

This study uses large-eddy simulations to analyze unsteady high-lift mechanisms from heaving flat plates at Reynolds 40,000, revealing significant lift enhancement due to vortex dynamics, especially at 13 degrees angle of attack.

## Contribution

It isolates heaving motion to investigate flow physics and lift enhancement, demonstrating the role of vortex formation at high Reynolds numbers in unsteady aerodynamics.

## Key findings

- Lift increases up to 17% over steady flow.
- Maximum lift coefficient of 2.1 at 13 degrees.
- Lift surpasses quasi-steady predictions by 24%.

## Abstract

Flapping animal flight is often modeled as a combined pitching and heaving motion in order to investigate the unsteady flow structures and resulting forces that could augment the animal's lift and propulsive capabilities. This work isolates the heaving motion of flapping flight in order to numerically investigate the flow physics at a Reynolds number of 40,000, a regime typical for large birds and bats and challenging to simulate due to the added complexity of laminar to turbulent transition in which boundary layer separation and reattachment are traditionally more difficult to predict. Periodic heaving of a thin flat plate at fixed angles of attacks of 1, 5, 9, 13, and 18 degrees are simulated using a large-eddy simulation (LES). The heaving motion significantly increases the average lift compared with the steady flow, and also surpasses the quasi-steady predictions due to the formation of a leading edge vortex (LEV) that persists well into the static stall region. The progression of the high-lift mechanisms throughout the heaving cycle is presented over the range of angles of attack. Lift enhancement compared with the equivalent steady state flow was found to be up to 17% greater, and up to 24% greater than that predicted by a quasi-steady analysis. For the range of kinematics explored it is found that maximum lift enhancement occurs at an angle of attack of 13 degrees, with a maximum lift coefficient of 2.1, a mean lift coefficient of 1.04.