Abstract
Successful icing/de-icing simulations for rotorcraft require a good prediction of the convective heat transfer on the blade’s surface. Rotorcraft icing is an unwanted phenomenon that is known to cause flight cancelations, loss of rotor performance and severe vibrations that may have disastrous and deadly consequences. Following a series of experiments carried out at the Anti-icing Materials International Laboratory (AMIL), this paper provides heat transfer measurements on heated rotor blades, under both the anti-icing and de-icing modes in terms of the Nusselt Number (Nu). The objective is to develop correlations for the Nu in the presence of (1) an ice layer on the blades (NuIce) and (2) liquid water content (LWC) in the freestream with no ice (NuWet). For the sake of comparison, the NuWet and the NuIce are compared to heat transfer values in dry runs (NuDry). Measurements are reported on the nose of the blade-leading edge, for three rotor speeds (Ω) = 500, 900 and 1000 RPM; a pitch angle (θ) = 6°; and three different radial positions (r/R), r/R = 0.6, 0.75 and 0.95. The de-icing tests are performed twice, once for a glaze ice accretion and another time for rime ice. Results indicate that the NuDry and the NuWet directly increased with V∝, r/R or Ω, mainly due to an increase in the Reynolds number (Re). Measurements indicate that the NuWet to NuDry ratio was always larger than 1 as a direct result of the water spray addition. NuIce behavior was different and was largely affected by the ice thickness (tice) on the blade. However, the ice acted as insulation on the blade surface and the NuIce to NuDry ratio was always less than 1, thus minimizing the effect of convection. Four correlations are then proposed for the NuDry, the NuWet and the NuIce, with an average error between 3.61% and 12.41%. The NuDry correlation satisfies what is expected from heat transfer near the leading edge of an airfoil, where the NuDry correlates well with Re0.52.
Highlights
Helicopters play an increasingly important role in both military and civil transportation
Rotorcraft blades are usually thinner and smaller compared to fixed wing aircraft, adding to the complexity of the addition of an ice protection system
This paper presents numerical and experimental work conducted by the École de Technologie Supérieure (ÉTS) and the Anti-icing Materials International Laboratory (AMIL), with the ultimate goal of validating the developed numerical tools for heat transfer calculation on a small helicopter tail rotor
Summary
Helicopters play an increasingly important role in both military and civil transportation. Rotorcraft blades are usually thinner and smaller compared to fixed wing aircraft, adding to the complexity of the addition of an ice protection system. This is why electrothermal heaters are currently considered the most, if not the only, available ice protection system available for rotor blades [3]. These systems operate in either the anti-icing or de-icing mode [2]. Ice is allowed to form at certain locations and time intervals before the heaters are activated and the ice is shed; the process is repeated throughout flight and could offer a more economical solution for ice protection
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