Analysis on Aerodynamic Performance of Finite Swept Wing with Glaze Ice Accretions

A computational investigation was performed to predict the effects of aerodynamic performance degradation on aircraft swept taper wing with and without 10 minutes and 22.5 minutes glaze ice accretions. In this study, the three-dimensional simulated glaze ice shapes were defined from a series of two-dimensional ice sections. The aerodynamic performances of glaze iced swept wings with C-H structure multi-block grid were analyzed and evaluated. The steady Reynolds- Averaged Navier-Stokes （RANS） equations are employed to compute solutions with implementation of two equation Shear-Stress Transport （SST） turbulence model and second-order upwind differencing for entire iced wing flow field. Computed results were compared with available experimental data. The CFD computation can also accurately predict the aerodynamic performance degradation of lift, drag and pressure coefficients of finite swept wing with glaze ice accretions which have two big upper and lower horn.

HYBRID AIRFOIL DESIGN FOR FULL-SCALE ICE ACCRETION TEST

A hybrid airfoil inverse design method according to the target pressure distribution and the impingement efficiency is presented.The method is developed to design hybrid airfoils that simulate the droplet impingement and ice accretion of full-scale airfoil.Flow field and droplet impingement around the full-scale airfoil are calculated to obtain pressure distribution and impingement efficiency firstly.The Navier-Strokes(N-S)solver is used in flow field calculation to improve calculation precision.The droplet impingement and ice accretion on the airfoil are performed by FENSAP-ICE.Once the target chord or original airfoil is given,the hybrid airfoil geometries can be computed.The designed hybrid airfoil consists of full-scale leading edges and redesigned aft-section.The hybrid airfoil can be tested under full-scale conditions to produce full-scale ice accretion in the exiting icing tunnels which are too small to perform ice accretion testing of full-scale airfoils.Moreover,the ice shapes formed on the full-scale and hybrid airfoils are compared at various attack angles.The results demonstrate that ice shapes between hybrid and full-scale airfoils match well and the developed method is effective.

Numerical analysis of ice accretion effects at super-cooled large droplet conditions on airfoil aerodynamics

Changes in flow field around NACA23012 airfoil from a clean condition to a super-cooled large droplet （SLD） condition were simulated, and variations in aerodynamic parameters were calculated using FLUENT. In the case of numerical simulation for a clean airfoil, flow field characteristics simulated agreed well with theory analysis, indicating that turbulence models and parameters setting are feasible. Aerodynamic parameters for iced airfoil were calculated using the same method and agreed with those measured test data under the same environment in icing wind tunnels by S. Lee. Conclusion is made that the numerical simulation is valid, and it can be an alternative to study ice accretion effects at the SLD condition on airfoil aerodynamics, leading to reduction in research cycle time and cost.

Wind Tunnel Test and Numerical Computation on Ice Accretion on Blade Airfoil for Straight-bladed VAWT

To invest the condition of ice accretion on the blade used for straight-bladed vertical axis wind turbine （SB-VAWT）, wind tunnel tests were carried out on a blade with NACA0015 airfoil by using a small simple icing wind tunnel. Tests were carried out at some typical attack angles under different wind speeds and flow discharges of a water spray with wind. The icing shape and area on blade surface were recorded and measured, Then the numerical computation was carded out to calculate the lift and drag coefficients of the blade before and after ice accretion according to the experiment result, the effect of icing on the aerodynamic characteristics of blade were discussed.

The Influence of Freezing Drizzle on Wire Icing during Freezing Fog Events

Both direct and indirect effects of freezing drizzle on ice accretion were analyzed for ten freezing drizzle events during a comprehensive ice thickness, fog, and precipitation observation campaign carried out during the winter of 2008 and 2009 at Enshi Radar Station （30°17′N, 109°16′E）, Hubei Province, China. The growth rate of ice thickness was 0.85 mm h-1 during the freezing drizzle period, while the rate was only 0：4 mm h-1 without sleet and freezing drizzle. The rain intensity, liquid water content （LWC）, and diameter of freezing drizzle stayed at low values. The development of microphysical properties of fog was suppressed in the freezing drizzle period. A threshold diameter （Dc） was proposed to estimate the influence of freezing drizzle on different size ranges of fog droplets. Fog droplets with a diameter less than Dc would be affected slightly by freezing drizzle, while larger fog droplets would be affected significantly. Dc had a correlation with the average rain intensity, with a correlation coefficient of 0.78. The relationships among the microphysical properties of fog droplets were all positive when the effect of freezing drizzle was weak, while they became poor positive correlations, or even negative correlations during freezing drizzle period. The direct contribution of freezing drizzle to ice thickness was about 14.5%. Considering both the direct and indirect effects, we suggest that freezing drizzle could act as a ＂catalyst＂ causing serious icing conditions.

APPLICATION OF CFD TECHNOLOGY IN WIND TURBINE ICING PROBER DESIGN

A series of numerical methods,which are suitable to design the shape and configuration of the icing prober for the horizontal axis wind turbine,are presented.The methods are composed of a multiple reference frame(MRF)method for calculating flow field of air,a Lagrangian method for computing droplet trajectories,an Eulerian method for calculating droplet collection efficiency,and an arithmetic for fast computing ice accretion.All the numerical methods are based on the computational fluid dynamics(CFD)technology.After proposing the basic steps and ideas for the design of the icing detection system,the shape and configuration of the icing prober for a 1.5 MW horizontal axis wind turbine are then obtained with the methods.The results show that the numerical methods are efficient and the CFD technology plays an important role in the design process.

Numerical Simulation of the Wake Generated by a Helicopter Rotor in Icing Conditions

The wake generated by the rotor of a helicopter can exert a strong interference effect on the fuselage and the horizontal/vertical tail.The occurrence of icing on the rotor can obviously make this interplay more complex.In the present study,numerical simulation is used to analyze the rotor wake in icing conditions.In order to validate the overall mathematical/numerical method,the results are compared with similar data relating to other tests;then,different simulations are conducted considering helicopter forward flight velocities of 0,10,20,50,and 80 knots and various conditions in terms of air temperature(atmospheric temperature degrading from−12°C to−20°C or from−20°C to−26°C).The results indicate that the rotor aerodynamic performance(i.e.,the lift-to-drag ratio distribution of the rotor disc)drops significantly once the rotor undergoes ice accretion.More importantly,the icing exerts a different influence of the wake dynamics depending on the atmospheric conditions.Interestingly,the rime-ice firstly occurs on the inner portion of rotor blades and then diffuses outward along the blade radial direction with the decrease in atmospheric temperature.

Estimating and Mapping Extreme Ice Accretion Hazard and Load Due to Freezing Rain at Canadian Sites

The ice accretion load in Canadian structural design codes is developed based on an operational ice accretion prediction model.In the present study,three models are employed to predict the ice accretion amount on a flat surface and horizontal wire at Canadian sites.The results confirm that the model used by Canadian practice for predicting ice accretion leads to a conservative estimate as compared to the remaining two models.The results also indicate that the use of the Gumbel distribution for the annual maximum ice accretion is adequate for regions prone to ice accretion and that the lognormal distribution may be considered for regions with a moderate or negligible amount of ice accretion.Maps of the ice accretion hazard at five selected Canadian sites are developed.Statistical analysis of an equivalent wind speed that is concurrent with the iced wire is carried out,showing that the concurrent wind speed for the 50-year return period value of the annual maximum ice accretion amount is smaller than the 50-year return period value of the annual maximum wind speed.It is shown that the statistical characteristics of the annual maximum concurrent wind speed on iced wire differ from that of the annual maximum wind speed.

Numerical simulation of rime ice accretion on a threedimensional wind turbine blade using a Lagrangian approach

The accreted ice on wind turbine blades significantly deteriorates the blade aerodynamic performance and consequently the power production.The existing numerical simulations of blade icing have mostly been performed with the Eulerian approach for two-dimensional(2D)blade profiles,neglecting the possible three-dimensional(3D)rotating effect.This paper conducts a numerical simulation of rime ice accretion on a 3D wind turbine blade using the Lagrangian approach.The simulation results are validated through previously published experimental data.The icing characteristics along the blade radial direction are then investigated in detail.Significant radial airflow along the blade is observed,which demonstrates the necessity of 3D simulation.In addition,more droplets are found to impinge on the blade surface near the tip region,thereby producing severer ice accretion there.The accreted ice increases almost linearly along the blade radial direction in terms of both ice mass and maximum ice thickness.

Thermal Feature Analysis of a New Hot-Air Anti-Icing Structure

Ice accretion on surfaces of the aircraft and engine is a serious threat to the flight safety.In this paper,a novel hot air anti-icing method is proposed based on the porous foam.Taking the NACA0012 airfoil as an example,the traditional thermal protection structure is proved to exist the deficiency in balancing the heat exchange caused by route loss of the heat.By dividing the hot chamber into multiple regions to fill with various foam metal,flow resistance characteristics and heat transfer characteristics for this protection mode are analyzed in order to derive the maximized benefit in anti-icing process.The calculation results reveal that,under the same condition,the region filled with foamed copper not only improves the temperature uniformity on the anti-icing area,but also achieves a better protection effect for enhancing heat transfer between the tube and the hot gas,averagely above 20℃higher than it without porous foam filling in surface temperature.Additionally,the minimum mass flow rate of the protection hot air is reduced by 16.7%.The gratifying efficiency of the porous filler in fortifying heat transfer confirms the potential of replacing the efficient but complex heat transfer design with simple structure filled with foam metal.