Measurement of Unsteady Aerodynamic Characteristics of a Heaving Wing in a Low Reynolds Number Flow

Abstract

The objective of this study is to determine the two-dimensional unsteady aerodynamic forces and moment acting on a heaving wing in a uniform flow using a wind tunnel. However, it is difficult to measure the aerodynamic forces acting on the heaving wing due to measuring device oscillation and the large inertial force of the wing model. In this study, a new type of wind tunnel test, named ''heaving wind tunnel,'' was developed. Here, the wing model remains stationary as the wind tunnel oscillates with a heaving motion. The advantage of this experimental method is that the measurement results are unaffected by the large inertial force acting on the oscillating wing model. Therefore, the wing model can be used in the same way as in steady state experiments. The normal force, thrust and pitching moment coefficients of a heaving airfoil were measured using the heaving wind tunnel test developed in this study. Through flow visualizations and pressure measurements, we found that the rapid drop in normal force coefficient after it reached its maximum value was due to a large growing leading-edge vortex.

Coupled Aerodynamics–Structure Analysis and Wind Tunnel Experiments on Passive Hinge Oscillation of Wing-Tip-Chained Airplanes

“…In a typical steady airflow, the values for flat plate C L start to show noticeable discrepancies between the linear theoretical values and experimental values outside this AoA region [33] under typical steady flow conditions. However, within the yellow line AoA at ±15 • , the flat plate has been proven to show lower discrepancy of mean C L values from ideal calculation values under oscilations perpendicular to the flow, or "heaving" by M. Okamoto et al [37,38], with the AoA of the peak C L increasing drastically compared to when in typical steady flow. This phenomenon is a result of the complex non-linear effects of flow seperation and reattachment but is worth noting.…”

“…The proposed method using numerical calculations was validated using chained flat wings in a small-scale low-speed wind tunnel and was confirmed to capture the oscillation trend well, although the flow state, that is the relative AoA, was outside the typical scope of VLM usage during some instances in the tested cases. This is the result of the complicated mechanisms of flow separation and reattachment effect of the wing "heaving" towards the air flow and increasing the average C L in AoA areas where it would typically drop drastically in a laminar flow [37,38]. Although not exactly accounting for this phenomenon, this effect is thought to have led to a reduction in the discrepancy between the VLM-calculated results and the actual experimental wing oscillation results in relatively high AoA regions.…”