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Research Papers: Multiphase Flows

A Runback Criterion for Water Drops in a Turbulent Accelerated Boundary Layer

[+] Author and Article Information
Edward B. White, Jason A. Schmucker

Department of Aerospace Engineering,  Texas A&M University, College Station, TX 77840

J. Fluids Eng 130(6), 061302 (May 19, 2008) (6 pages) doi:10.1115/1.2917429 History: Received June 22, 2007; Revised March 10, 2008; Published May 19, 2008

Predicting the runback threshold for liquid drops in aerodynamic boundary layers is a challenging problem with numerous applications including aircraft icing simulations. The critical parameters that govern drop runback are investigated in this experiment by using a wind tunnel that provides a turbulent accelerated flow similar to flows near an unswept wing’s leading edge. The experiments feature water drops on aluminum with a contact angle of 70±5deg. Results show that significant water∕air interface unsteadiness precedes drop runback. This is likely due to air-flow separation in the drop wakes. For displacement-thickness-scaled Reynolds numbers ranging from 348 to 429, a constant-Weber-number runback threshold We=3.45±0.09 is found to adequately correlate the runback results.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the Flow Lab test section. Dimensions are in millimeters.

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Figure 2

Boundary layer velocity profiles, U(y∕δ*) and urms′(y∕δ*); f(y∕δ*) is an arbitrary fit used to calculate Uh

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Figure 3

Characteristic images of drops in still air. The plate surface is superposed; the drops’ reflections are seen below this line.

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Figure 4

Drop runback behavior. Each point represents a single drop with some drops offset from their correct Reδ* value where multiple data points would overlap.

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Figure 5

Video images of a typical drop movement initiation

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