heat transfer from ice accretion steven mart baylor university scholar’s day: aeronautical &...

Heat Transfer from Ice Accretion

Steven MartBaylor University

Scholar’s Day: Aeronautical & Processing ApplicationsRogers Engineering Building

February 1, 2008

A Study to Better Predict and Prevent Ice Buildup on Aircraft Wings

Outline

• Basic Aerodynamic Definitions• Aircraft Icing Background

– The Problems– Ice Formation– Ice Removal

• Research Model & Goals• Questions

Basic Aerodynamic Definitions

• Chord- Distance between the leading and trailing edge of a wing, measured in the direction of the normal airflow

• Angle of attack (α)- Angle between the chord line and the relative airflow

• Reynolds Number (Re)- Ratio of inertial forces to viscous forces

Lift

DragV

RelativeWind

Viscous

MomentumVc

ReNumber Reynolds

Leading Edge

Trailing Edge

Why Icing Is A Problem

• Icing is serious flight safety concern

• Most serious during take-offs and landings (high lift demands)

• With ice, must fly at higher angles of attack (higher drag)

• Ice causes early separation – Lift drops drastically– Flow no longer in contact with control

surfaces

Why Icing Is A Problem (cont.)

Courtesy: Gent et al. (2000)

The Accretion of Ice

• Shape, amount and type of ice determined by:– Velocity– Temperature– Liquid Water Concentration (LWC)– Droplet Size (MVD)– Ice Accretion Time (

AIRFOILCLOUD OF SUPERCOOLED WATER DROPLETS

V

Ice Spectrum

• Rime and glaze ice are the two main varieties of aircraft ice

• Mixed ice, a combination of both rime and glaze ice, can also form

• Will focus on glaze ice during experimentation due to its tendency to form during take-offs and landings

Rime Ice Glaze IceMixed Ice

Glaze Ice

In general, occurs at temperatures near 32oF and high LWCs

Drops do not freeze on impact Ice is clear Horns may appear Surface tends to be covered

with roughness elements Physical mechanism of

formation not well understood

V=225 mph

Ttotal=25 OF

LWC=0.75 g/m3

MVD=20 m

=5 minutes

Icing Prevention and Removal Techniques

Anti-icing (ice prevention):• Heated wings-Hot compressor

bleed air is directed into sections of the wing increasing its surface temperature

• Weeping wings-Fluid (a water and glycol mix) is pumped through a mesh panel on the wings leading edge

• Clean wings can also be sprayed with glycol based fluids to protect against freezing for a limited time

Deicing (ice removal):• Pneumatic boots-attached to

wings and are inflated with air in order to break off any ice that has accumulated on them

• If wings have accumulated ice, a heated glycol and water mix is sprayed on the wings to remove it

Goals of Research

• Looking to expand on the research of Henry, Hansman, and Breuer (1995).

• Henry et al. was the first to study the heat transfer of a scale roughness element

• Assumed conduction through plate and surface radiation to ambient were negligible

• Trying to further their findings by considering the effects of conduction through the plate

• Establish a better understanding of what physical events are transpiring

Research Model

• Thin plate with simulated ice accumulation

• Use of the Baylor University Subsonic Wind Tunnel to establish a controlled airflow

• Measure the heat transfer across the plate with infrared cameras

Baylor University Wind Tunnel

24” by 24” Test SectionTest Range: 0 – 150 ft/s Open loop tunnel

•Larger test area will allow for a larger scale model reducing the required velocity of airflow in order to match Reynolds number

Potential Impacts

• Open the door for further research• Allow for more complex and precise simulations of

ice accretion• Capability to better predict and prevent the icing of

aircraft

Summary

• Glaze ice is a serious problem due to its susceptibility to form during take-offs and landings, when lift demands are at their greatest

• Looking to expand upon the research of Henry et al. with the consideration of plate conduction

• Attempting to gain a better understanding of the heat transfer due to glaze icing

Thank you!

Questions?