New 3-D ice accretion method of hovering rotor including effects of centrifugal force

Local convective heat transfer coefficients were measured from a smooth NACA 0012 airfoil having a chord length of 0.533 m. Flight data were taken for the smooth airfoil at Reynolds numbers based on chord in the range 1.24 to 2.50 million and at various angles of attack up to 4 deg. During these flight tests, the freestream velocity turbulence intensity was found to be very low. Wind tunnel data were acquired in the Reynolds number range 1.20 to 4.52 million and at angles of attack from -4 to +8 deg. The turbulence intensity in the IRT was 0.5-0.7 percent with the cloud-generating sprays off. A direct comparison between the results obtained in flight and in the IRT showed that the higher level of turbulence intensity in the IRT had little effect on the heat transfer for the lower Reynolds numbers but caused a moderate increase in heat transfer at the higher Reynolds numbers. Turning on the cloud-generating spray nozzle atomizing air in the IRT did not alter the heat transfer. The present data were compared with leading-edge cylinder and flat plate heat transfer correlations that are often used to estimate airfoil heat transfer in computer codes.

Heat transfer measurements from a smooth NACA 0012 airfoil

A new numerical method for predicting ice accretion on helicopter rotors is established. First, the orthogonal and body-fitted grids are generated around the rotor blade, and the computational flui...

Numerical Simulations for Ice Accretion on Rotors Using New Three-Dimensional Icing Model

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

Wind tunnel experiments were conducted in order to study the effect of a simulated glaze ice accretion on the flowfield of a semispan, reflection-plane, rectangular wing at Re = 1.5 million and M = 0.12. A laser Doppler velocimeter was used to map the flowfield on the upper surface of the model in both the clean and iced configurations at alpha = 0, 4, and 8 degrees angle of attack. At low angles of attack, the massive separation bubble aft of the leading edge ice horn was found to behave in a manner similar to laminar separation bubbles. At alpha = 0 and 4 degrees, the locations of transition and reattachment, as deduced from momentum thickness distributions, were found to be in good agreement with transition and reattachment locations in laminar separation bubbles. These values at y/b = 0.470, the centerline measurement location, matched well with data obtained on a similar but two dimensional model. The measured velocity profiles on the iced wing compared reasonably with the predicted profiles from Navier-Stokes computations. The iced-induced separation bubble was also found to have features similar to the recirculating region aft of rearward-facing steps. At alpha = 0 degrees and 4 degrees, reverse flow magnitudes and turbulence intensity levels were typical of those found in the recirculating region aft of rearward-facing steps. The calculated separation streamline aft of the ice horn at alpha = 4 degrees, y/b = 0.470 coincided with the locus of the maximum Reynolds normal stress. The maximum Reynolds normal stress peaked at two locations along the separation streamline. The location of the first peak-value coincided with the transition location, as deduced from the momentum thickness distributions. The location of the second peak was just upstream of reattachment, in good agreement with measurements of flows over similar obstacles. The intermittency factor in the vicinity of reattachment at alpha = 4 degrees, y/b = 0.470, revealed the time-dependent nature of the reattachment process. The size and extent of the separation bubble were found to be a function of angle of attack and the spanwise location. Three dimensional effects were found to be strongest at alpha = 8 degrees. The calculated separation and stagnation streamlines were found to vary little with spanwise location at alpha = 0 degrees. The calculated separation streamlines at alpha = 4 degrees revealed that the bubble was largest near the centerline measurement plane, whereas the tip-induced vortex flow and the model root-tunnel wall boundary-layer interaction reduced the size of the bubble. These effects were found to be most dramatic at alpha = 8 degrees.

An Experimental Study of the Flowfield on a Semispan Rectangular Wing With a Simulated Glaze Ice Accretion

This study addresses the analytical assessment of the degradation in the forward flight performance of the front rotor Boeing Vertol CH47D helicopter in a rime ice natural icing encounter. The front rotor disk was divided into 24 15-deg sections and the local Mach number and angle of attack were evaluated as a function of azimuthal and radial location for a specified flight condition. Profile drag increments were then calculated as a function of azimuthal and radial position for different times of exposure to icing, and the rotor performance was re-evaluated including these drag increments. The results of the analytical prediction method, such as horsepower required to maintain a specific flight condition, as a function of icing time have been generated. The method to illustrate the value of such an approach in assessing performance changes experienced by a helicopter rotor as a result of rime ice accretion is described.

Performance Degradation of Helicopter Rotor in Forward Flight Due to Ice

The analytical model described by Korkan et al. (1982) for predicting the performance degradation of propellers in a natural icing encounter is used to determine the feasibility of predicting helicopter performance degradation in hover during natural icing. The flight condition selected for analysis involves an altitude of 3000 ft and a free-air temperature of 1 F. The values of degradation yielded by the model for rime ice accretion are representative of those experienced in actual flight.

Helicopter rotor performance degradation in natural icing encounter

A theoretical ice accretion model has been established applicable to both aircraft propellers and helicopter rotors to determine the effect of rime ice on the thrust, power, and efficiency as a function of exposure time in a natural icing condition. Comparisons have been made of theoretical performance levels with previously published experimentally determined propeller thrust and efficiency for five natural icing conditions. Agreement between test and theory was acceptable.

Performance degradation of propeller systems due to rime ice accretion

A theoretical model has been established which is applicable to both propeller and helicopter systems that determines the effect of rime ice accretion on the thrust coefficient, power coefficient, and efficiency as a function of time in a natural icing condition. Theoretical comparisons have been made with experimentally determined decrease in propeller thrust coefficient and efficiency for five natural icing conditions with good agreement. The present analytical model is also applicable to the helicopter case, where the method predicts radial and azimuthal rotor blade ice shapes in addition to torque rise as a function of time in a natural icing condition.

Performance degradation of propeller/rotor systems due to rime ice accretion

Methodology developed to predict the performance degradation of rotating systems in natural icing conditions is described and discussed. Theoretical studies of the increments performance degradation due to icing involving the propeller, helicopter in hover and forward flight, and XV-15 propulsion modes are summarized. Related experimental studies on the NACA 0012 airfoil and model helicopter with/without generic ice shapes are reviewed. The results of these experimental and theoretical studies are used to suggest refinements to current methodology.

R. J. Shaw

Papers

Performance Degradation of Helicopter Rotor in Forward Flight Due to Ice

Helicopter rotor performance degradation in natural icing encounter

Performance degradation of propeller systems due to rime ice accretion

Performance degradation of propeller/rotor systems due to rime ice accretion

Performance degradation of helicopters due to icing - A review