Showing papers on "Glaze ice published in 2008"

Numerical simulation of ice accretion on airfoils

Abstract: Summary An approach to numerically simulate ice accretion on airfoils has been developed and used to characterize ice accretion on a NACA0012 airfoil. In this paper we present the background and motivation for the investigation, the techniques used, and then the main results are presented. The validation of the simulation approach developed in this paper is also discussed. Finally, the conclusions are presented based on our analysis of the results presented. BACKGROUND INTRODUCTION Ice accretion on airplane wings can be a hazard to flight safety. The cause of the accretion is due to supercooled water droplets impinging to the windward face of the wings. Ice accretion can modify the designed aerodynamic shape of airfoils and considerably degrade their aerodynamic performance. Thus, being able to evaluate the mechanisms and consequences of ice accretion is of great importance to anti-icing and de-icing. Different icing conditions form different type of ice accretions. Depending on the icing mechanism, ice accretions can be classified as: rime ice, glaze ice or mixed ice. Rime ice occurs in a low temperature environment and forms because supercooled droplets freeze simultaneously when they impinge onto the airfoil surface. Glaze ice occurs in an environment with relatively high temperature (while still lower than freezing point) under which the droplets freeze partially at the impingement location and then freeze gradually during the flow along the airfoil surface caused by airflow. Mixed ice is defined as a mixture of rime and glaze ice. Glaze ice and mixed ice can corrupt the designed aerodynamic shape of airfoils more significantly than rime ice. These forms of ice accretion can be investigated by several means, including flight test, experimental simulation, engineering method and numerical simulation. Flight test and experimental simulation can obtain exact ice shape but are usually too expensive to be widely adopted. The engineering method uses the typical experimental data and empirical formulae but could hardly analyze the ice accretion process. Therefore, numerical simulation is widely adopted because it is economical and can simulate the icing process and so provide a relatively exact evaluation of ice accretion. Several codes for simulating ice accretion have been developed internationally, such as: LEWICE (USA), ONERA (France), DRA (UK), FENSAP-ICE (Canada), CIRAMIL (Italy). TECHNIQUES DESCRIPTION This paper develops an approach to numerically simulate ice accretion on airfoils which is based on four modules: (1) air flowfield solution, (2) droplets collection efficiency calculation, (3) boundary layer characteristics evaluation, and (4) ice accumulation evaluation via a thermodynamic model. Air flowfield solution The air flowfield can be obtained by using the panel method to solve the Euler equations or directly solving the compressible Navier-Stokes equations. The panel method can calculate the air velocity at any point in the flowfield directly but usually lacks accuracy in computing the complete flowfield. In contrast, the solution of the compressible Navier-Stokes equations can provide a more accurate flowfield computation but is time consuming. In order to synthetically consider the computational precision and efficiency, an Euler flow computation is adopted in this paper. Droplets collection efficiency calculation The droplets’ collection efficiency on the airfoil surface is important in numerically simulating ice accretion and two computational methods are available: Lagrangian and Eulerian two-phase flows methods. The Lagrangian method obtains the collection efficiency by solving the motion equation of droplets to track each droplet’s trajectory in the flowfield. Eulerian two-phase flow methods consider the droplets in the airflow as a form of pseudo fluid which interpenetrates with the air and the collection efficiency is obtained through solving the velocity and apparent density distribution of droplets. There are advantages in using the Eulerian two-phase flow method compared with a Lagrangian approach since the same mesh can be used to solve the governing equations for the airflow and droplets. Also, the droplets’ collection efficiency may be obtained based on the solution of the droplets’ flowfield directly, meaning that particles don’t have to be tracked. For these reasons the Eulerian two-phase flows method has been adopted here.

Computational study of the Effects of Ice Accretions on the Flowfields in the M2129 S-Duct inlets

Abstract: Typical rime and glaze ice accretion shape on the lip of the M2129 S-duct inlets are computationally simulated and their effects on the inlet duct performance are investigated by steady-state RANS solutions. Glaze ice accretion produces serious degradation of the inlet duct performance, while the effect of rime ice shape is negligible. Significant changes in flowfield property distributions inside the inlet ducts are observed for glaze ice accretion due to its obstructive shape to the inflow. Compared to the clean inlet, the secondary flow region at the engine face of the duct inlet is increased by 600 percent for the glaze iced inlet. Total pressure recoveries at the engine face for the rime and glaze ice case are 98.8 and 95.8 percent, respectively. Also, glaze ice causes 26 percent reduction in the mass flow rate at the inlet duct throat. Nomenclature th D = Throat diameter (m) LWC = Liquid water contents ( ) 3 g/m MVD = Mean volume diameter ( m μ ) th M = Throat Mach number (~) M∞ = Freestream Mach number (~) S p = Static pressure (Pa) t p = Total pressure (Pa) t p ∞ = Freestream total pressure (Pa)

Improvement of runback water film calculation and its impact on ice prediction

Abstract: Over the past few decades, aircraft icing has been the subject of numerous studies. Ice accretion on an aircraft can damage its aerodynamic performance. It can also have a devastating affect on structures such as high voltage pylons. The simulation of ice accretion represents an important technological breakthrough in the understanding of ice behaviour as well as an alternative to expensive experiments. Although numerical models will probably never replace wind tunnel experiments, they continuously progress and benefit from the latest advances in computing techniques. ICECREMO2 is a new generation model and uses an unstructured grid approach. Unstructured meshes offer real advantages in the generation of complex grid structures but also provide support for grid adaptivity. Adaptivity consists in improving the resolution only in some aspects of the solution. It offers the benefits of the high resolution without the computational overhead of classical structured methods. Adaptive methods are usually more difficult to implement and the application to the equation coupling water film and ice growth has never been investigated before this work. The mathematical model used in ICECREMO describes both the water film flow and the ice growth. This allows us to better predict glaze ice accretion when a runback water film is present. The equation describing the thin film water flow is a complex non-linear fourth-order degenerate partial differential equation. To resolve complex features such as a moving front, high resolution numerical methods are necessary. Such a numerical scheme has been developed for this equation in a previous study on structured grid, and has proven to be reliable. In this work Sweby’s scheme has been reformulated in a finite volume framework, an error estimator has been defined for our adaptive mesh refinement method and a grid refinement strategy has been implemented which follows the water film front and keeps it under high resolution. Finally, the impact of the improved resolution of the water film on the glaze ice growth is investigated. Results obtained with first-order and high resolution methods have been compared on different model problems under various conditions. At the end an extension of the refinement strategy is proposed by defining error estimators with respect to the ice layer and by combining it with a multi-step procedure.

Artificial rime ice

Abstract: The invention relates to a making method for an artificial glaze ice; so far, the rime seen by people is made by nature. The technical scheme provided in the invention is as follows: the jet flow of liquid nitrogen and water sprays towards a certain direction and intersects together, the sprayed water is fog-shaped, the fog-shaped matter rapidly reaches a supercooled state, the supercooled fog-shaped matter is sprayed to the target matter in order to make the glaze ice; the invention has the advantages of beautifying the environment, the artificial scenery, bringing the enjoyment of beauty to people and attracting people to nature; therefore, the artificial glaze ice can be used in large parks, human landscape and so on.

Effects of Ice Formation on the Flowfield of an Aircraft Engine Inlet

Abstract: The effects of typical rime and glaze ice on the performance of the M2129 S-duct inlet are computationally investigated using the steady-state RANS solution. The glaze ice accretion produces a substantial degradation of the inlet performance due to its obstructive shape to the in-flow, while the effect of the rime ice is not significant. Compared to the clean inlet, the secondary flow region at the engine face of the duct inlet is increased by 600 percent for the glaze iced inlet. Total pressure recoveries at the engine face for the rime and glaze ice case are 98.8 and 95.8 percent, respectively. Also, the glaze ice causes 26 percent reduction in the mass flow rate at the engine face. In addition, the adverse effects on the performance of the inlet are enhanced by an increase in freestream Mach numbers due to the stronger and more extensive shock formations in the inlet flow. With increasing free stream Mach numbers from M∞ = 0.13 to 0.85, total pressure recovery decreases from 0.985 to 0.62 with the glaze ice accretion. And the level of the mass flow rate with the glaze ice accretion is 76 percent of that in ice-free condition at M∞ = 0.13; however, it decreases to 68 percent at M∞ = 0.475.Copyright © 2008 by ASME

Ice Accretion Simulation On Finite Wings WithExtended Messinger Method

Abstract: Numerical icing simulations on finite wings are performed using a quasi-3D approach. The solution method consists of computations of the flowfield using the Hess-Smith panel method, droplet trajectories, droplet collection efficiencies, convective heat transfer coefficients and finally ice accretion rates and ice shapes. Inputs to the problem are the ambient temperature Ta , freestream velocity V∞, liquid water content of air ρa , droplet diameter dp, total icing time texp, angle of attack α and the wing geometry. Droplet trajectories are calculated by integrating the differential equations of motion for the droplets over time. Droplet impact locations and collection efficiencies are thus determined. Convective heat transfer coefficients are calculated using empirical relations and the solutions of the 2-D integral boundary layer equations. Extended Messinger Method is employed for the prediction of the ice accretion rates. At low temperatures and liquid water contents rime ice occurs and the ice thickness is obtained using an algebraic equation. At higher temperatures and liquid water contents, glaze ice forms for which the energy and mass conservation equations are combined to yield a first order ordinary differential equation, solved numerically. In this case, a thin layer of water is present over a layer of ice and effects of runback water are accounted for. A computer code is developed using the outlined theory, which is validated with experimental ice shapes reported in the literature. Ice shapes are obtained for a wing having taper, twist, dihedral and sweep.

Effect of ice geometry to airfoil performance using neural networks prediction

Abstract: Purpose – The purpose of this paper is to describe a methodology for predicting the effects of glaze ice geometry on airfoil aerodynamic coefficients by using neural network (NN) prediction. Effects of icing on angle of attack stall are also discussed. Design/methodology/approach – The typical glaze ice geometry covers ice horn leading-edge radius, ice height, and ice horn position on airfoil surface. By using artificial NN technique, several NNs are developed to study the correlations between ice geometry parameters and airfoil aerodynamic coefficients. Effects of ice geometry on airfoil hinge moment coefficient are also obtained to predict the angle of attack stall. Findings – NN prediction is feasible and effective to study the effects of ice geometry on airfoil performance. The ice horn location and height, which have a more evident and serious effect on airfoil performance than ice horn leading-edge radius, are inversely proportional to the maximum lift coefficient. Ice accretions on the after-location of the upper surface of the airfoil leading edges have the most critical effects on the airfoil performance degradation. The catastrophe of hinge moment and unstable hinge moment coefficient can be used to predict the stall effectively. Practical implications – Since the simulation results of NNs are shown to have high coherence with the tunnel test data, it can be further used to predict coefficients at non-experimental conditions. Originality/value – The simulation method by using NNs here can lay the foundation of the further research about the airfoil performance in different ice cloud conditions through predicting the relations between the ice cloud conditions and ice geometry.

Experimental Researches on Micro-Droplet Freezing on a Solid Surface Under Atmospheric Conditions: Part I

Abstract: Atmospheric ice accretion on structures is a problem of fundamental importance to a number of industries. Examples of engineering problems caused by ice accretion involving aircraft, power transmission lines, telecommunication towers, electrical railway contact-wires, and other structures. Under atmospheric icing conditions two basic types of ice may form; rime or glaze. The supercooled micro-droplets in clouds are an important factor in icing. The objective of this study was to develop a new experimental method to investigate a single supercooled micro-droplet freezing process, in order to better understand the mechanism of rime or glaze ice accretion. The experimental device and principles are described in this paper. The experimental set has two small cold rooms, which is separated by a board with a central hole. A droplet with diameter of 15∼40 μm, temperature of 0∼−5°C was levitated in the cold air stream by electrostatic force. A CCD camera tracked its trace. The air temperature is from 0∼−10°C, the micro-droplet diameter is from 15∼40μm, and its temperature is from 0∼−5°C in the experimental study. This article focused on the experimental set and the experimental principles, and the next article will focus on the experimental data analysis.Copyright © 2008 by ASME