Estimation of Chaotic Surface Pressure Characteristics of Ice Accreted Airfoils–A 0–1 Test Approach

Abstract

Airfoils have their respective applications in almost every engineering field ranging from wind turbine blades, aircraft, and cooling fans to sophisticated electronic components. Thus, the flow over the airfoils is of primary focus to engineers in developing appropriate applications to meet the current standards in technology as well as demands. However, the underlying surface pressure characteristics need significant attention to understand the flow over airfoils completely. Generally, the flow over an airfoil and the time series pressure on the surface is linear and hence the aerodynamic forces are considered to be linear. But as the flow is perturbed due to external disturbances, nonlinearities creep in, and the surface pressure characteristics exhibit nonlinear behaviour. The ice accretion on the leading edge of the airfoil was witnessed to be an opportunity to investigate the nonlinear surface pressure characteristics. The current experimental study aims to investigate the dynamics of the surface pressure characteristics of four distinct ice geometries on the NACA0012 airfoil at a Reynolds number of $2\times 10^{5}$ . The angle of attack of the airfoil was varied from 0° to 24° with an increment of 3°. The 0–1 test for chaos was applied to the ice accreted airfoils at all the pressure ports on the suction surface of the airfoil. The test gives a single value for K, known as the asymptotic growth rate of the mean squared displacement. The value of K = 0 implies that the underlying dynamics could be periodic and when the value of K = 1, the underlying dynamics show aperiodicity and hence chaos. The horn iced airfoil performed significantly weaker compared to other ice accretion geometries because a significantly higher amount of chaos was produced in the flow field due to the presence of a geometry resembling a separation bubble. This aided in the substantial increment in drag and loss of lift for the horn ice accreted airfoil.

Keywords

• Brownian motion
• chaos
• horn ice
• ice accretion
• rime ice
• separation bubble