Canonical Shear Flow Interactions with Unsteady Airfoils
Abstract
A coordinated experimental and computational investigation is carried out to determine how the basic flow physics of steady and unsteady airfoils are altered when the upstream approach flow is changed from the traditional uniform conditions to that of non-uniform flow. Our particular objectives are to establish the alterations that occur for both the load on the airfoil and also the flow field structure. This work considers the NACA 0012 airfoil in pure pitch with low to moderate angle of attack amplitudes about zero mean angle of attack, and chord Reynolds number of order 10,000. It is found that a steady symmetric airfoil has negative lift at zero angle of attack when placed in steady shear flow with positive shear, opposite of the prediction of inviscid theory. A hypothesis is formulated to explain the observed sign of the lift force on the basis of the asymmetry in boundary layer development on the upper and lower surfaces of the airfoil, which creates an effective airfoil shape with negative camber. However, it is found that the same steady airfoil placed in the unsteady flow field of a two-stream shear layer generates positive lift at zero angle of attack. Also, the character of the (CL - alpha) curve changes fundamentally and the multi-slope features of the curve in the case of uniform flow completely disappear in favor of a much longer linear region characteristic of much higher Reynolds number airfoils. The main influence of shear approach flow on unsteady aerodynamic load is on the mean lift, leaving the mean thrust and force fluctuations mostly unaffected
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 13, 2018
- Accession Number
- AD1062084
Entities
People
- Manoochehr Koochesfahani
Organizations
- Michigan State University