Guy Fortin

Wind Turbine Icing and De-Icing

This paper presents the wind turbine icing challenge, explains the wind turbine icing process and how to address the problem of icing and de/anti-icing wind turbines. The physics of ice accretion is explained such as rime and glaze ice accretion as well as how meteorological parameters such as air speed and temperature, altitude, liquid water content and water droplet median volumetric diameter, as well as wind turbine rotational speed and blade profile impact on ice accretion. Numerical methods to predict water droplet trajectories, ice accretion and aerodynamic performance degradation are presented. These methods can aid in the positioning of de/anti-icing systems. A recommendation for the positioning of deicing systems in the profile section and along the blade is provided.

Spinning Rotor Blade Tests in Icing Wind Tunnel

The Spinning Rotor Blade (SRB) is an apparatus developed at Anti-icing Material International Laboratory in collaboration with Bell Helicopter Textron to study ice physics, low energy de-icing systems and hydro- or ice-phobic coatings use for small helicopters. The SRB is a 1/18 subscale model of a small helicopter with 0.78 m diameter rotor of two blades rotated by a 10 hp engine to a tip speed of 130 m/s. The blades are 6066-T6 extruded aluminum with a NACA0012 airfoil of 69.64 mm chord and 0.315 m long. The icing tests were conducted in AMIL’s low speed closed loop Icing Wind Tunnel with a liquid water content of 0.84 g/m³, a median volumetric diameter of 26.7 ± 2.6 µm, an air speed of 15 ± 0.5 m/s and temperature of -15 ± 0.5°C. The power to rotate the SRB was 1 200 ± 120 W with a vibration of 2 ± 0.4 g; when the icing began, the power increased to 5 200 ± 1 400 W at a rate of 30 ± 4 W/s, suddenly, after 160 ±50 s, the power decreased, indicating that a piece of ice of 70 ± 15 mm length and about 4 g of weight was shed at the blade tip. The SRB is able to perform reproducible ice shedding tests with similar behavior to helicopters at low cost with repeatability below 30% and sensibility of ±5% for temperatures ranging from -5 to -20oC. The ice adhesive shear stress estimated from the SRB II at -15°C was 0.21 ± 0.06 MPa for aluminum. It decreased linearly when the temperature increased. Also, the adhesive shear stress obtained for icephobic Coating A was 0.10 MPa which is 2.1 less adhesive than aluminum, but its icephobicity is insufficient to be safely used on helicopters. Some empirical correlations for ice thickness, freezing fraction and adhesive shear stress were found with the SRB-II and also a criterion was proposed criterion to quantify the icephobicity of coating efficiency for helicopters, but without fundamental parametric scaling equations to helicopter, they are not helpful for helicopter.

New Roughness Computation Method and Geometric Accretion Model for Airfoil Icing

This paper presents recent developments in wet and dry ice accretion simulation at AMIL (AntiIcing Materials International Laboratory), in a joint project with CIRA (Italian Aerospace Research Center). This paper introduces an analytical model to calculate the surface roughness and the remaining, runback, and shedding liquid water mass on an airfoil surface. Three analytical formulations are used to calculate the local roughness height based on the maximum height that a bead can reach before moving and the wave height on a water film. A mass balance is used to determine the remaining and runback water masses when the water state and the maximum bead height are known. The water shedding mass is determined using a simple mass model. A new method is used to build the accreted ice surface on the airfoils. It uses the bisection of the angle between adjacent panels to determine ice shape. The new roughness computation method and the geometric model generate the complex ice shapes observed experimentally and the results agree well with icing profiles obtained in wind tunnel experiments.

Experimental Study of Hybrid Anti-Icing Systems Combining Thermoelectric and Hydrophobic Coatings

Two commercial hydrophobic coatings: StaClean™ with a water droplet contact angle of 101°and Wearlon® Super F1-Ice with a contact angle of 115°and one superhydrophobic coating: HIREC 1450 with a contact angle of 152° were studied combined with a thermoelectric anti-icing system under icing conditions. All coatings and the reference surface were tested under glaze and rime ice. The deicing tests were conducted in the Anti-icing Materials International Laboratorys (AMIL) low speed closed loop Icing Wind Tunnel with 0.4 g/m3 liquid water content, a 26.7 ± 2.6 μm water droplet median volumetric diameter, 21 ± 0.5 m/s air speed and temperatures of -5 and -20 ± 0.5°C. For these tests, a 4′ chord NACA 63-415 airfoil 2D blade box-section of 10′ covered with a thin aluminum sheet protected at the leading edge and on the bottom by a thermoelectric anti-icing system composed of two ′ × 10′ heating elements with a power density of 40 W/in2, was used. The superhydrophobic coating showed excellent results with a power reduction of 13% for rime ice and 33% for glaze ice. Hydrophobic coatings performed at a lower level than the superhydrophobic coatings with a power reduction of about 8% for rime ice and 13% for glaze ice, but their effect was still significant. Also, the coatings significantly improved the runback water, most probably due to their hydrophobic nature. For the superhydrophobic coating, the surface was mostly free of ice due to the fact that drops roll over the surface to the trailing edge and for hydrophobic coatings, the runback back water froze outside the protected area; with time, a barrier developed which stopped runback water and ice accumulation increased with time. For rime and glaze ice accretion, the higher the contact angle, the more effective the coating; which suggests that a superhydrophobic surface with a high contact angle could significantly reduce the anti-icing power required.

PREDICTION OF 2D AIRFOIL ICE ACCRETION BY BISECTION METHOD AND BY RIVULETS AND BEADS MODELING

The paper presents recent developments in wet and dry ice accretion simulation at AMIL (Anti-Icing Materials International Laboratory) in a joint project with CIRA (Italian Aerospace Research Center). The thermodynamic model of ice accretion is similar to existing ones developed by LEWICE in USA, DRA in British, ONERA in France and Ecole Polytechnique de Montreal in Canada. However, this paper introduces an analytical model to calculate the surface roughness in the wet regime based on the residual, runback and shedding liquid water mass on an airfoil surface. Also, a new geometric model to build the ice surface, based on panel angle bisections, is presented. In the wet regime, the empirical LEWICE correlation used to determine the equivalent sand-grain roughness is replaced by two analytical formulations to calculate the local roughness height. The first one considers the maximal height that the bead can reach before moving, while the second computes the wave height on the water film. The maximum bead height before moving is determined from the equilibrium between aerodynamic, gravitational and surface tension forces. The bead behavior in dry and wet regimes was described analytically Based on the work of Al-Khalil and Hansman, which led to the determination of a water surface state (film, rivulets or beads). A mass balance is used to determine the residual and runback mass of water when the water state and the maximal bead height before moving are known. The water shedding mass is equal to the runback water mass for the lower surface and is zero for the upper surface of the airfoil respectively. A geometrical model based on panel bisection allows the ice growth in normal direction to the surface. This method simulates the ice surface accretion continually without gaps between panels. The accretion model is validated with icing profiles obtained experimentally in wind tunnel by Shin and Bond for a NACA0012 wing profile with a 0.5334 m chord, a 20 µm median volume droplet diameter, a 1 g/m³ liquid water content and a 65 m/s airspeed. These results cover both ice accretion regimes in the -4.4° to -28.3°C temperature interval. The roughness calculated analytically is in the same order of magnitude as LEWICE correlation. The use of analytical models for roughness generated the complex icing shapes (horn) as the ones observed experimentally. However, in most cases, the accreted ice was slightly bigger than the measured.

Software tool to predict the Wind Energy production losses due to icing

The icing causes energy losses for wind turbines. Impact of ice is difficult to quantify without experimental tests and numerical simulations due to the lack of real data from the field. The high cost of wind tunnel testing, conducted to the necessity to develop a numerical approach that can accurately evaluate the energy losses for different configurations of wind turbine and weather conditions at lower cost and over a shorter period. PROICET is a numerical model to calculate the annual energy production of a wind turbine considering the icing events. This model can elsewhere quantify the energy losses induced by the ice.

Prediction of Ice Shapes on NACA0012 2D Airfoil

The objective of this communication is to present the new capability at AMIL in ice accretion simulation on 2D Airfoils at low speed. AMIL, in a joint project with CIRA (Italian Aerospace Research Center), has developed a numerical model called CIRAMIL. This model is able to predict ice shapes in wet and dry regimes. The thermodynamic model used is similar to existing ones. The major difference is in the approach of calculating the surface roughness and the residual, runback and shedding liquid water masses on an airfoil surface. The numerical ice shapes are compared to rime and glaze shapes obtained experimentally in wind tunnel for a NACA0012 wing profile. The new roughness computation method generates the complex ice shapes observed experimentally in wet and dry regimes and the results agree well with icing profiles obtained in wind tunnel experiments and in many cases are better than those predicted by the models available.

Experimental Study of Snow Precipitation Over a Generic Deicing Fluid without Fluid Flow

Deicing and anti-icing fluids are used to remove and prevent ice formation on aircraft before takeoff. Holdover times (HOT) published by the FAA are used by pilots as guidelines indicating the amount of effective time of a fluid under certain freezing precipitation types. However, the times on these tables are based on endurance time tests involving a visual estimate of failure on a flat plate [1]: when 30% of the fluid is covered with white snow under snow precipitation, although the times have been correlated to aircraft wing tests [2] they do not address the mechanism of fluid failure. To measure and understand the fluid mechanisms conducting to failure, the Anti-icing Materials International Laboratory (AMIL) developed a simplified test with a generic deicing propylene glycol-based fluid. The test consisted of pouring 400 mL of the generic deicing fluid on a 5 dm by 3 dm level flat plate where the plate edges were rimmed with insolated walls to make a waterproof open box. The flat plate covered with deicing fluid was submitted to snow precipitation in the form of regular snow and simulated snow pellets. The snow precipitation intensities and temperatures tested were based on ARP5485. The standard test method for testing snow indoors includes using a heating pad to compensate for the lack of thermal equilibration which occurs in outside with wind and the larger air mass. It was the energy solicited by the fluid melting the snow from the heat pad that was used to develop a model for fluid failure. Three precipitation intensities and eight temperatures with the generic deicing fluid and commercial Type I and Type IV fluids were studied. At fluid failure, snow mass, and energy provided to melt the snow were independent of snow intensity and type of snow, however endurance time and supplied power were dependent on snow intensity but independent of snow type. Visual observations showed that only a fraction of the falling snow in contact with the fluid covering the aluminium plate melts, the unmelted snowflakes descend by gravity into the fluid and accumulate on the aluminium plate surface. The energy to melt the snow was provided by a heating system. The proposed model assumes that enough energy is available to melt all the snow that a deicing fluid is able to absorb under water form and that the water can diffuse rapidly into the deicing fluid due to multiple diffusion sites resulting in an uniform propylene glycol concentration and predicted well the endurance time and the snow mass at fluid failure for a generic deicing and Type I fluid with an error of 7%. A semi-empirical relation was used in the model to evaluate the melting fraction; this relation, based on a phase diagram, can be used to estimate the propylene glycol concentration, the power and the energy as a function of time at the fluid failure. However, the model could not predict the endurance time of Type IV anti-icing fluids.

Aerodynamic Flow-off of Type II and Type IV Aircraft Ground Anti-icing Fluids

The certification process for aircraft ground anti-icing fluids involves flat plate wind tunnel aerodynamic flow-off tests. This test method was developed in 1990 from flight and wind tunnel tests results on full scale and model airfoils, and flat plates; the resulting lift losses were then correlated to the Boundary Layer Displacement Thickness (BLDT) on a flat plate. This correlation was made for Type II fluids existing at the time. Since the introduction of Type IV fluids in 1994, with significantly longer anti-icing endurance times, the same test procedure was applied. However, Type IV fluids are generally more viscous than Type II fluids of the same concentration. At the FAAs request, a study was undertaken to see if aerodynamic certification testing should be different for Type IV fluids as opposed to Type II. After a comparison of existing certification BLDT data which showed no significant differences between Type II and Type IV fluids, aerodynamic tests were performed on five commercial fluids, two typical Type II and three typical Type IV fluids. Tests with different initial thickness showed that the thickness had little effect on BLDT and fluid elimination data, with the exception of one fluid, near the temperature at which it is acceptable. Examination of energy data showed that more energy was required by the wind tunnel to move the Type II fluids as opposed the Type IV fluids. When these fluids were tested using an identical fixed fan speed profile at 0, -10 and -25°C, little difference was seen in the BLDTs as compared to those generated by a certification profile adjusted to obtain the same acceleration. These preliminary tests suggest that the aerodynamic certification method developed for Type II fluids is adequate for assessing Type IV fluids.

TIDAL SEDIMENTATION IN GROS-CACOUNA HARBOR

The equations describing conservation of mass, momentum and energy in a turbulent free surface flow are derived for a controle volume extending over the whole depth. The effect of the turbulent surface oscillations are discussed but neglected in the following analysis, where the equations are applied to the energy balance in a surf zone wave motion. This leads to results for the wave height variation and the velocity of propagation. The results cannot be reconciled completely with measurements and the concluding discussion is aimed at revealing how the model can be improved.A three-dimensional morphodynamic model of sequential beach changes Is presented. The model Is based on variations in breaker wave power generating a predictable sequence of beach conditions. The spectrum of beach conditions from fully eroded-dissipatlve to fully accreted reflective is characterised by ten beach-stages. Using the breaker wave power to beach-stage relationship the model Is applied to explain temporal, spatial and global variations In beach morphodynamlcs.The agents of initial damage to the dunes are water, which undermines them, and animals (including man) which damage the protective vegetation by grazing or trampling. Of these, man has recently assumed predominant local importance because of the popularity of sea-side holidays and of the land-falls of certain marine engineering works such as oil and gas pipelines and sewage outfalls. The need is therefore increasing for active dune management programmes to ensure that under these accentuated pressures, the coast retain an equilibrium comparable with that delicately balanced equilibrium which obtains naturally at a particular location.