Heat Transfer from Ice Accretion

1、Heat Transfer from Ice AccretionSteven MartBaylor UniversityScholars Day: Aeronautical & Processing ApplicationsRogers Engineering BuildingFebruary 1, 2008A Study to Better Predict and Prevent Ice Buildup on Aircraft WingsOutline Basic Aerodynamic Definitions Aircraft Icing Background The Proble

2、ms Ice Formation Ice Removal Research Model & Goals QuestionsBasic Aerodynamic DefinitionsChord- Distance between the leading and trailing edge of a wing, measured in the direction of the normal airflowAngle of attack ()- Angle between the chord line and the relative airflowReynolds Number (Re)-

3、 Ratio of inertial forces to viscous forcesLiftDragVRelativeWindViscousMomentumVcReNumber ReynoldsLeading EdgeTrailing EdgeWhy 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 (highe

4、r drag) Ice causes early separation Lift drops drastically Flow no longer in contact with control surfacesWhy 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 (MV

5、D) Ice Accretion Time (t)AIRFOILCLOUD OF SUPERCOOLED WATER DROPLETSVIce SpectrumRime and glaze ice are the two main varieties of aircraft iceMixed ice, a combination of both rime and glaze ice, can also formWill focus on glaze ice during experimentation due to its tendency to form during take-offs a

6、nd landings Rime IceGlaze IceMixed IceGlaze 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 understoodV=225 mphTtotal=25 OFLWC=0.75

7、g/m3 MVD=20 m t=5 minutesIcing Prevention and Removal TechniquesAnti-icing (ice prevention):Heated wings-Hot compressor bleed air is directed into sections of the wing increasing its surface temperatureWeeping wings-Fluid (a water and glycol mix) is pumped through a mesh panel on the wings leading e

8、dgeClean wings can also be sprayed with glycol based fluids to protect against freezing for a limited timeDeicing (ice removal):Pneumatic boots-attached to wings and are inflated with air in order to break off any ice that has accumulated on themIf wings have accumulated ice, a heated glycol and wat

9、er mix is sprayed on the wings to remove itGoals 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 Tr

10、ying to further their findings by considering the effects of conduction through the plate Establish a better understanding of what physical events are transpiringResearch Model Thin plate with simulated ice accumulation Use of the Baylor University Subsonic Wind Tunnel to establish a controlled airf

11、low Measure the heat transfer across the plate with infrared camerasAir FlowTo Boundary-Layer Bleed FanTest PlateTestSectionInfraredCameraBaylor University Wind Tunnel24” by 24” Test SectionTest Range: 0 150 ft/s Open loop tunnel Larger test area will allow for a larger scale model reducing the requ

12、ired velocity of airflow in order to match Reynolds numberPotential 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 aircraftSummary Glaze ice is a serious problem due to its susceptibility to form during take-offs and landings, when lift demands are at their greatest Look