Effects of ice accretions on aircraft aerodynamics

Progress toward the development of a method for predicting the flowfield of an iced airfoil is described and shown to offer the prospect of a priori calculations of the effects of ice accretion and roughness on airfoil performance. The approach is based on interaction of inviscid flow solutions obtained by a panel method and improved upon by a finite-difference boundary-layer method which, operating in an inverse mode, incorporates viscous effects including those associated with separated flows. Results are presented for smooth, rough and iced airfoils as a function of angle of attack. Those for smooth and rough airfoils confirm the accuracy of the method and its applicability to surfaces with roughness similar to that associated with insect deposition and some forms of ice. Two procedures have been developed to deal with large ice accretion and their performance is examined and shown to be appropriate to the engineering requirements.

Calculation of Flow Over Iced Airfoils

The experimental evidence for the effects of rain, insects, and ice on airfoil performance are examined. The extent to which the available information can be incorporated in a calculation method in terms of change of shape and surface roughness is discussed. The methods described are based on the interactive boundary layer procedure of Cebeci or on the thin layer Navier Stokes procedure developed at NASA. Cases presented show that extensive flow separation occurs on the rough surfaces.

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Effects of enviromentally imposed roughness on airfoil performance

An experimental study has been conducted in the OSU subsonic tunnel to measure the detailed aerodynamic characteristics of an airfoil with simulated glaze ice. A special model was built with interchangeable leading edges to be used in this study. One leading edge is that of a NACA 0012, while the other is a simulation of a glaze ice accretion measured in the NACA Lewis Icing Research Tunnel. The model was instrumented with a dense distribution of surface pressure taps to provide excellent detail around the ice shapes and reattachment point. A traversing total pressure probe was used to document the boundary layer characteristics on the NACA 0012 section. The ice shape caused a severe lift and drag penalty, reducing the maximum lift by over 50 percent and causing a 300 percent increase in drag. Surface pressure distributions revealed a large lower surface separation in addition to the expected large upper surface separation.

Aerodynamic measurements of an airfoil with simulated glaze ice

This paper describes the development of an innovative control architecture that integrates Flush-air data system with Reconfigurable Control to yield an intelligent prognostic on-line control augmentation and Health and Efficiency Monitoring (FaRCHEM) system. A proof-of-concept FaRCHEM system was developed using a Fouga (CM 170) aircraft as the test platform. The functionality of FaRCHEM system architecture was demonstrated through various simulations examples of different flight scenarios. In particular, the proof-of-concept study demonstrated the capability of the FaRCHEM system by simulating some example aircraft health degradation and/or failure situations and showing how the FaRCHEM system offers graceful recovery through pro-active corrective control actions. The proposed control architecture uses prognostic sensory feedback in the form of instantaneous pressure levels obtained from Flush Air Data System (FADS) in reconfigurable feedback control configuration to provide stability augmentation and/or performance enhancement. The instantaneous pressure signature of the aircraft is effectively used to assess the health of the aircraft. The FaRCHEM system provides valuable information to pilot about imminent anomalies in flight conditions that may lead to potential failures. This pilot alert system will enable pilot to take corrective action to avoid potential failure. The reconfigurable control system uses its control re-allocation capability to redistribute control signal in the event of any actuator/sensor failures. I. Introduction

Aircraft Control Augmentation and Health Monitoring using Flush Air Data System Feedback

An experimental study has been conducted in the OSU subsonic tunnel to measure the characteristics of the separation bubble on an airfoil with glaze ice. A measured glaze ice accretion on a NACA 0012 airfoil was simulated in wood for this dry tunnel test. The 21 inch chord model was pressure belted and the ice shape internally tapped to obtain surface pressures, lift and moment coefficients. A wake survey probe was used to obtain airfoil drag. The separation bubble was explored by measuring the time averaged velocities using a split film probe. The probe was positioned using a computer controlled two-dimensional traversing system. In this paper, airfoil lift, drag, and moment coefficient data are compared for the airfoil with and without glaze ice. Velocity profiles in the separation bubble are presented for several chordwise stations at three angles of attack. The ice shape caused a severe lift and drag penalty. The velocity profiles show clearly the large bubble geometry, regions of reversed flow, and bubble reattachment.

W. J. Coirier

Papers

Detailed measurements of the flowfield in the vicinity of an airfoil with glaze ice