Jose Palacios

Ultrasonic De-Icing of Wind-Tunnel Impact Icing

Ultrasonic excitation has proven to provide ice-interface transverse shear stresses exceeding the adhesion strength of freezer ice to various metals, promoting instantaneous ice delamination. Wind-tunnel impact ice presents challenges that are not encountered when removing freezer ice. The low-power, nonthermal ultrasonic de-icing concept is investigated under impact-icing conditions in an icing wind tunnel. In this research effort, ultrasonic actuator disks excite isotropic plates and airfoil-shaped structures that are representative of helicopter leading-edge protection-cap shapes. Off-the-shelf ultrasonic actuators are used to create ice-interface shear stresses sufficient to promote instantaneous ice delamination of thin layers of impact ice (less than 3 mm thick). A steel plate of 30.48 cm x 30.48 cm x 1 mm was actuated by three lead zirconate titanate disks excited at their ultrasonic radial mode. The ultrasonic vibration introduced transverse shear stresses that prevented ice formation on top of the actuator locations for a fraction of the power required with electrothermal systems used in helicopter rotor blades (0.18 W/cm 2 vs 3.8 W/cm 2 ). Experiments also showed ice delamination in areas of the plates where transverse shear stresses were concentrated. As ice thicknesses reached a critical value of approximately 1.2 mm, ice debonded from those steel-plate areas. A model of the three disk actuated steel plate was created and correlated with experimental results observed during impact-icing test experiments. Both, the predicted ultrasonic modes of the system and the ice-shedding areas agreed with experimental results. In addition, a second set of experiments involving NACA 0012 airfoil-shaped structures were conducted. Actuators located on the top and bottom surfaces of the leading-edge cap were actuated with an input power as low as 200 W (32 kHz ultrasonic mode). Thin layers of ice (less than 2 mm thick) constantly delaminated from the leading edge of the airfoil on those regions where stress concentrations were predicted.

Instantaneous De-Icing of Freezer Ice via Ultrasonic Actuation

A low-power, nonthermal, ultrasonic de-icing system is introduced as a potential de-icing system for helicopter rotor blades. In this research effort, ultrasonic actuators excite isotropic plates and airfoil-shaped structures that are representative of helicopter leading-edge protection caps. The system generates delaminating ultrasonic transverse shear stresses at the interface of accreted ice, debonding thin ice layers (less than 3 mm thick) as they form on the isotropic host structure. A finite element model of the proposed actuator and the isotropic structures with accreted ice guides the selection of the actuator prototypes. Several actuator-isotropic plate structures are fabricated and tested under freezer ice conditions. Test results demonstrate that radial resonance disk actuators (28-32 kHz) create ultrasonic transverse shear stresses capable of instantaneously delaminating ice layers. The finite element modeling predicts the delamination patterns of the accreted ice layers. Models also predict (within 15%) the required input voltage to promote instantaneous ice debonding. At environment temperatures of -20°C, the system delaminates 2.5-mm-thick ice layers with power input densities as low as 0.07 W/cm 2 (0.5 W/in. 2 ).

Genetic learning of the membership functions for mining fuzzy association rules from low quality data

Many methods have been proposed to mine fuzzy association rules from databases with crisp values in order to help decision-makers make good decisions and tackle new types of problems. However, most real-world problems present a certain degree of imprecision. Various studies have been proposed to mine fuzzy association rules from imprecise data but they assume that the membership functions are known in advance and it is not an easy task to know a priori the most appropriate fuzzy sets to cover the domains of the variables. In this paper, we propose FARLAT-LQD, a new fuzzy data-mining algorithm to obtain both suitable membership functions and useful fuzzy association rules from databases with a wide range of types of uncertain data. To accomplish this, first we perform a genetic learning of the membership functions based on the 3-tuples linguistic representation model to reduce the search space and to learn the most adequate context for each fuzzy partition, maximizing the fuzzy supports and the interpretability measure GM3M in order to preserve the semantic interpretability of the obtained membership functions. Moreover, we propose a new algorithm based on the Fuzzy Frequent Pattern-growth algorithm, called FFP-growth-LQD, to efficiently mine the fuzzy association rules from inaccurate data considering the learned membership functions in the genetic process. The results obtained over 3 databases of different sizes and kinds of imprecisions demonstrate the effectiveness of the proposed algorithm.

Tracking control of piezoelectric stack actuator using modified Prandtl–Ishlinskii model

This article presents the development of Prandtl–Ishlinskii hysteresis model and tracking control of piezoelectric stack actuator with severe hysteresis. Classical Prandtl–Ishlinskii model is a linearly weighted superposition of many backlash operators with different threshold and weight values, which inherits the symmetric property of the backlash operator at about the center point of the loop formed by the operators. To describe the asymmetric hysteresis of piezoelectric stack actuators, two modified operators were developed, one for ascending branches and another for descending branches. Based on this modified model, a feedforward controller was designed to compensate the hysteresis. Since the modified model describes the inverse of hysteresis, the feedforward controller and the hysteresis of piezoelectric stack actuator canceled each other. To attenuate the creep effect and reduce tracking error, a feedback controller was proposed to work with the feedforward controller. Experimental results show that this control scheme that combines feedforward and feedback controllers greatly improves the tracking of the piezoelectric actuator and the error is less than 0.15 µm.

Active Gurney Flaps: Their Application in a Rotor Blade Centrifugal Field

Miniature trailing-edge effectors are segmented gurney flaps that can deploy to achieve multipurpose functions, such as performance enhancement, noise/vibration control, and/or load control on rotor blades. The unsteady aerodynamics of miniature trailing-edge effectors and a deployable plain flap (with an equivalent lift gain) are quantified experimentally at a reduced frequency of 0.21 and a Reynolds number of 1×106. These experiments are also simulated using computational fluid dynamics. The combination of the wind tunnel experiments and computational fluid dynamics are used to quantify the aerodynamic effects of miniature trailing-edge effector deployment to compare their unsteady aerodynamics to plain flaps, and to evaluate the fluid dynamics of miniature trailing-edge effectors against experimental data. The current experiments display unsteady aerodynamics that corroborate previous computational fluid dynamics findings that indicate that miniature trailing-edge effectors shed on-surface vortices dur...

Ice Particle Impacts on a Moving Wedge

This work presents the results of an experimental study of ice particle impacts on a moving wedge. The experiment was conducted in the Adverse Environment Rotor Test Stand (AERTS) facility located at Penn State University. The wedge was placed at the tip of a rotating blade. Ice particles shot from a pressure gun intercepted the moving wedge and impacted it at a location along its circular path. The upward velocity of the ice particles varied from 7 to 12 meters per second. Wedge velocities were varied from 0 to 120 meters per second. Wedge angles tested were 0 deg, 30 deg, 45 deg, and 60 deg. High speed imaging combined with backlighting captured the impact allowing observation of the effect of velocity and wedge angle on the impact and the post-impact fragment behavior. It was found that the pressure gun and the rotating wedge could be synchronized to consistently obtain ice particle impacts on the target wedge. It was observed that the number of fragments increase with the normal component of the impact velocity. Particle fragments ejected immediately after impact showed velocities higher than the impact velocity. The results followed the major qualitative features observed by other researchers for hailstone impacts, even though the reduced scale size of the particles used in the present experiment as compared to hailstones was 4:1.

Experimental Measurement of Frozen and Partially Melted Water Droplet Impact Dynamics

High-speed video of single frozen water droplets impacting a surface was acquired. The droplets diameter ranged from 0.4 mm to 0.9 mm and impacted at velocities ranging from 140 m/sec to 309 m/sec. The techniques used to freeze the droplets and launch the particles against the surfaces is described in this paper. High-speed video was used to quantify the ice accretion area to the surface for varying impact angles (30 deg, 45 deg, 60 deg), impacting velocities, and break-up angles. An oxygen /acetylene cross-flow flame used to ensure partial melting of the traveling frozen droplets is also discussed. A linear relationship between impact angle and ice accretion is identified for fully frozen particles. The slope of the relationship is affected by impact speed. Perpendicular impacts, i.e. 30 deg, exhibited small differences in ice accretion for varying velocities, while an increase of 60% in velocity from 161 m/sec to 259 m/sec, provided an increase on ice accretion area of 96% at an impact angle of 60 deg. The increase accretion area highlights the importance of impact angle and velocity on the ice accretion process of ice crystals. It was experimentally observed that partial melting was not required for ice accretion at the tested velocities when high impact angles were used (45 and 60 deg). Partially melted droplets doubled the ice accretion areas on the impacting surface when 0.0023 Joules were applied to the particle. The partially melted state of the droplets and a method to quantify the percentage increase in ice accretion area is also described in the paper.

Airfoil-Performance-Degradation Prediction Based on Nondimensional Icing Parameters

A physics-based empirical correlation between icing conditions and the corresponding drag coefficient was developed for NACA 0012 airfoils, and compared to other three existing prediction methods. The correlation was developed based on experimental aerodynamic databases of iced airfoils, and derived using statistical methods. The correlation model also provides drag coefficients for varying angles of attack for a given icing condition. The calculated drag coefficients resulted in 33.40% mean absolute deviation with respect to reference data from three different experimental databases. To validate the proposed degradation model and to further extend the database for helicopter-rotor performance degradation, rotating ice-accretion experiments were conducted. Four ice shapes obtained at the NASA Icing Research Tunnel were reproduced on a 53.34-cm-chord, 1.37-m-radius NACA 0012 rotor blade at the Adverse Environment Rotor Test Stand facility. Ice-shape molding and casting techniques were introduced to capture...

Analytical and Experimental Determination of Airfoil Performance Degradation due to Ice Accretion

A physics-based, empirical correlation between icing conditions and corresponding drag coefficient was developed for NACA 0012 airfoil and compared to other three existing prediction methods. The correlation was developed based on experimental aerodynamics database of iced airfoils and derived using statistical methods. The correlation model also provides drag coefficients for varying angles of attack under a given icing condition. The calculated drag coefficients matched (33.40% mean absolute deviation) with reference data from three different experimental databases. To validate the proposed degradation model and to further extend the database for helicopter rotor performance degradation, rotating ice accretion experiments were conducted. Four ice shapes obtained at the NASA Icing Research Center were reproduced on a 21-inch chord, 4.5-feet radius NACA 0012 rotor blade at the Adverse Environment Rotor Test Stand facility. Ice shape molding and casting techniques were introduced to capture delicate ice features such as ice feathers. The iced airfoil castings were tested in a dry-air wind tunnel. Performance degradation was compared between the four iced models and the clean airfoil. The effect of ice feathers on drag degradation was investigated. Ice feather formation can account for up to 25% of the drag introduced by ice accretion prior to stall. Comparison between the proposed analytical determination method and experimental results from both rotor ice testing and icing wind tunnel testing showed to be satisfactory, ranging from 25% to 6% depending on the icing condition.

Ultrasonic Shear and Lamb Wave Interface Stress for Helicopter Rotor De-Icing Purposes

Theoretical lamb and shear waves interface shear concentration coefficients values (ISCC) for steel - ice layered systems are predicted and superimposed to its correspondent ultrasonic dispersion curves. Those ultrasonic modes with high ISCC values are expected to enhance possible non-thermal de-icing capabilities as long as enough energy is provided to the system. As ice thickness increases, lamb waves generate up to 140% increases in ISCC values compared to that provided by shear waves, for a phase velocity range between 1 and 7Km/sec. The modes with higher ISCC for different ice thickness are identified. The theoretical dispersion curves used to evaluate the conceptual proposed de-icing system are experimentally acquired and compared to predicted results. The ultrasonic modes experimentally obtained match the theoretically predicted ones with a maximum error of 8%.