Calculated performance of the NASA Lewis icing research tunnel

The Icing Research Tunnel is used extensively to test many classes of aircraft under atmospheric icing conditions. Because of the need to test models at higher Reynolds numbers, a new fan rotor was designed to increase test section wind speed. A preliminary study was made of the present fan rotor to suggest possible methods to increase tunnel wind speed. The results of that study are presented

Optimal control of the heave motion of marine cable subsea-unit systems

One of the key problems associated with subsea operations involving tethered subsea units is the motions of support vessels on the ocean surface which can be transmitted to the subsea unit through the cable and increase the tension. In this paper, a theoretical approach for heave compensation is developed. After proper modelling of each element of the system, which includes the cable/subsea-unit, the onboard winch, control theory is applied to design an optimal control law. Numerical simulations are carried out, and it is found that the proposed active control scheme appears to be a promising solution to the problem of heave compensation

A new characterization of supercooled clouds below 10,000 feet AGL

Icing caused by supercooled clouds below 10,000 feet were characterized with a view toward a change in FAA standards for civil aircraft ice protection standards. Current techniques in cloud physics were employed

Morphological instability of the solid-liquid interface in crystal growth under supercooled liquid film flow and natural convection airflow

Ring-like ripples on the surface of icicles are an example of morphological instability of the ice-water interface during ice growth under supercooled water film flow. The surface of icicles is typically covered with ripples of about 1 cm in wavelength, and the wavelength appears to be almost independent of external temperature, icicle radius, and volumetric water flow rate. One side of the water layer consists of the water-air surface and growing ice is the other. This is one of the more complicated moving phase boundary problems with two interfaces. A recent theoretical work [K. Ueno, Phys. Rev. E 68, (2003) 021603] to address the underlying instability that produces ripples is based on the assumption of the absence of airflow around icicles. In this paper, we extend the previous theoretical framework to include a natural convection airflow ahead of the water-air surface and consider whether the effect of natural convection airflow on the wavelength of ripples produced on an ice surface is essential or not.Comment: 19 pages, 5 figure

Study of Airflow Behavior for Duplex Circular Cylinders

The modeling of atmospheric ice accretion on duplex cylinders received a limited attention, with modeling carried by Wagner and Qing et al. The publicly available experimental data about the ice accretion on the duplex cylinders is limited to experiments of Qing et al. and Veerakumar et al. When comparing the data of Wagner and Qing et al. with the results of Veerakumar et al., the major difference is the airflow behavior in the wake of the windward cylinder, the extent of the wake and recirculation bubble, and the velocity distribution in the wake. Thus, its needed to study the effect of the turbulence model on the airflow behavior of duplex cylinders, with focus being the behavior of the wake of the windward cylinder. This study reports the simulation results of the complex airflow behavior of duplex circular cylinder bundle obtained using several turbulence models employed by commercial CFD code

Atmospheric Ice Accretion Measurement Techniques

Atmospheric icing on structures has proven to be an area of concern in many cold climate geographical regions like arctic and alpine. Difficulties encountered by the communication, construction and power industries in these areas are the subject of intense investigations for researchers from decades. Three main methods of investigation are generally employed by researchers to study atmospheric ice accretion on structures: a) continuous field measurements, b) lab based simulations using icing wind tunnel & c) numerical modelling. This paper presents a brief review study of various techniques to understand and measure the atmospheric ice accretion on structures, anti/de icing techniques and important parameters for numerical modelling of atmospheric ice accretion

Superhydrophobic and icephobic surfaces prepared by RF-sputtered polytetrafluoroethylene coatings

A superhydrophobic and icephobic surface were investigated on aluminum alloy substrate. Anodizing was used first to create a micro-nanostructured aluminum oxide underlayer on the alloy substrate. In a second step, the rough surface was coated with RF-sputtered polytetrafluoroethylene (PTFE or Teflon®). Scanning electron microscopy images showed a “bird's nest”-like structure on the anodized surface. The RF-sputtered PTFE coating exhibited a high static contact angle of ~165° with a very low contact angle hysteresis of ~3°. X-ray photoelectron spectroscopy (XPS) results showed high quantities of CF3 and CF2 groups, which are responsible for the hydrophobic behavior of the coatings. The performance of this superhydrophobic film was studied under atmospheric icing conditions. These results showed that on superhydrophobic surfaces ice-adhesion strength was 3.5 times lower than on the polished aluminum substrate