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This presentation reports results from recent icing scaling tests in NASA Glenn Icing Research Tunnel (IRT) to evaluate how well the scaling method recommended for Appendix C conditions might apply to SLD conditions.
This report presents results from a joint study by DRA, NASA, and ONERA for the purpose of comparing, improving, and validating the aircraft icing computer codes developed by each agency. These codes are of three kinds: (1) water droplet trajectory prediction, (2) ice accretion modeling, and (3) transient electrothermal deicer analysis. In this joint study, the agencies compared their code predictions with each other and with experimental results. These comparison exercises were published in three technical reports, each with joint authorship. DRA published and had first authorship of Part 1 - Droplet Trajectory Calculations, NASA of Part 2 - Ice Accretion Prediction, and ONERA of Part 3 - Electrothermal Deicer Analysis. The results cover work done during the period from August 1986 to late 1991. As a result, all of the information in this report is dated. Where necessary, current information is provided to show the direction of current research. In this present report on ice accretion, each agency predicted ice shapes on two dimensional airfoils under icing conditions for which experimental ice shapes were available. In general, all three codes did a reasonable job of predicting the measured ice shapes. For any given experimental condition, one of the three codes predicted the general ice features (i.e., shape, impingement limits, mass of ice) somewhat better than did the other two. However, no single code consistently did better than the other two over the full range of conditions examined, which included rime, mixed, and glaze ice conditions. In several of the cases, DRA showed that the user's knowledge of icing can significantly improve the accuracy of the code prediction. Rime ice predictions were reasonably accurate and consistent among the codes, because droplets freeze on impact and the freezing model is simple. Glaze ice predictions were less accurate and less consistent among the codes, because the freezing model is more complex and is critically dependent upon unsubstantiated heat transfer and surface roughness models. Thus, heat transfer prediction methods used in the codes became the subject for a separate study in this report to compare predicted heat transfer coefficients with a limited experimental database of heat transfer coefficients for cylinders with simulated glaze and rime ice shapes. The codes did a good job of predicting heat transfer coefficients near the stagnation region of the ice shapes. But in the region of the ice horns, all three codes predicted heat transfer coefficients considerably higher than the measured values. An important conclusion of this study is that further research is needed to understand the finer detail of of the glaze ice accretion process and to develop improved glaze ice accretion models.
The effects of ice formations on the section lift, drag, and pitching-moment coefficients of an unswept NACA 65A004 airfoil section of 6-foot chord were studied.. The magnitude of the aerodynamic penalties was primarily a function of the shape and size of the ice formation near the leading edge of the airfoil. The exact size and shape of the ice formations were determined photographically and found to be complex functions of the operating and icing conditions. In general, icing of the airfoil at angles of attack less than 40 caused large increases in section drag coefficients (as much as 350 percent in 8 minutes of heavy glaze icing), reductions in section lift coefficients (up to 13 percent), and changes in the pitching-moment coefficient from diving toward climbing moments. At angles of attack greater than 40 the aerodynamic characteristics depended mainly on the ice type. The section drag coefficients generally were reduced by the addition of rime ice (by as much as 45 percent in 8 minutes of icing). In glaze icing, however, the drag increased at these angles of attack. The section lift coefficients were variably affected by rime-ice formations; however, in glaze icing, lift increases at high angles of attack amounted to as much as 9 percent for an icing time of 8 minutes. Pitching-moment-coefficient changes in icing conditions were somewhat erratic and depended on the icing condition. Rotation of the iced airfoil to angles of attack other than that at which icing occurred caused sufficiently large changes in the pitching-moment coefficient that, in flight, rapid corrections in trim might be required in order to avoid a hazardous situation.
A two-phase wind tunnel test was conducted in the 6 by 9 foot Icing Research Tunnel (IRT) at NASA Lewis Research Center to evaluate the effect of ice on the performance of a full scale general aviation wing. In the first IRT tests, rime and glaze shapes were carefully documented as functions of angle of attack and free stream conditions. Next, simulated ice shapes were constructed for two rime and two glaze shapes and used in the second IRT tunnel entry. The ice shapes and the clean airfoil were tapped to obtain surface pressures and a probe used to measure the wake characteristics. These data were recorded and processed, on-line, with a minicomputer/digital data acquisition system. The effect of both rime and glaze ice on the pressure distribution, Cl, Cd, and Cm are presented.
The thin-skin heat rate technique was used to determine local convective heat transfer coefficients for four representative ice accretion shapes. The shapes represented three stages of glaze ice formation and one rime ice formation; the ice models had varying degrees of surface roughness. In general, convective heat transfer was higher in regions where the model's surfaces were convex and lower in regions where the surfaces were concave. The effect of roughness was different for the glaze and rime ice shapes. On the glaze ice shapes, roughness increased the maximum Nu by 80 percent, but the other Nu values were virtually unchanged. On the rime ice shape, the Nu numbers near the stagnation point were unchanged. The maximum Nu value increased by 45 percent, and the Nu number downstream of the peak increased by approximately 150 percent.
This report presents results from the first icing tests performed in the Modem Airfoils program. Two airfoils have been subjected to icing tests in the NASA Lewis Icing Research Tunnel (IRT). Both airfoils were two dimensional airfoils; one was representative of a commercial transport airfoil while the other was representative of a business jet airfoil. The icing test conditions were selected from the FAR Appendix C envelopes. Effects on aerodynamic performance are presented including the effects of varying amounts of glaze ice as well as the effects of approximately the same amounts of glaze, mixed, and rime ice. Actual ice shapes obtained in these tests are also presented for these cases. In addition, comparisons are shown between ice shapes from the tests and ice shapes predicted by the computer code, LEWICE for similar conditions. Significant results from the tests are that relatively small amounts of ice can have nearly as much effect on airfoil lift coefficient as much greater amounts of ice and that glaze ice usually has a more detrimental effect than either rime or mixed ice. LEWICE predictions of ice shapes, in general, compared reasonably well with ice shapes obtained in the IRT, although differences in details of the ice shapes were observed.
A method for characterizing ice shapes using a self-organizing map (SOM) technique is presented. Self-organizing maps are neural-network techniques for representing noisy, multi-dimensional data aligned along a lower-dimensional and possibly nonlinear manifold. For a large set of noisy data, each element of a finite set of codebook vectors is iteratively moved in the direction of the data closest to the winner codebook vector. Through successive iterations, the codebook vectors begin to align with the trends of the higher-dimensional data. In information processing, the intent of SOM methods is to transmit the codebook vectors, which contains far fewer elements and requires much less memory or bandwidth, than the original noisy data set. When applied to airfoil ice accretion shapes, the properties of the codebook vectors and the statistical nature of the SOM methods allows for a quantitative comparison of experimentally measured mean or average ice shapes to ice shapes predicted using computer codes such as LEWICE. The nature of the codebook vectors also enables grid generation and surface roughness descriptions for use with the discrete-element roughness approach. In the present study, SOM characterizations are applied to a rime ice shape, a glaze ice shape at an angle of attack, a bi-modal glaze ice shape, and a multi-horn glaze ice shape. Improvements and future explorations will be discussed.
A full scale general aviation wing with a NACA 63 sub 2 A415 airfoil section was tested to determine icing characteristics for representative rime and glaze icing conditions. Measurements were made of ice accretion shapes and resultant wing section drag coefficient levels. It was found that the NACA 63 sub 2 A415 wing section was less sensitive to rime and glaze icing encounters for climb conditions.
The present investigation is concerned with the icing characteristics of a general aviation wing section, taking into account selected results from icing wind tunnel tests of the wing section. Drag coefficient increases of about 130 percent were measured for a 20 minute glaze icing encounter and cruise aerodynamic conditions. The drag increased by about 40 percent for a 15 minute rime icing encounter and the same aerodynamic conditions. The considered wing section was found to be less sensitive to rime and glaze ice accretions occurring for the climb aerodynamic conditions. The observed aft frost layer growths contributed significantly to the measured increase in section drag coefficient level. Comparisons of measured increases in section drag coefficient due to the primary ice accretion with predictions of NACA drag correlation indicated agreement was as good as that for the original data upon which the correlation was based.
There are four areas of research being pursued in 1988 under sponsorship of the FAA/NASA Joint University Research Program, and one area which has been completed. The four active areas were: (1) Automatic Speech Recognition (ASR) in Air Traffic Control. The purpose of this research effort is to demonstrate the feasibility of using ASR technology within the ATC environment and to address the problems involved, especially the relevant human factors issues. (2) A Rule-Based Planning and Scheduling System. Planning denotes the formulation of a detailed scheme, program, or method worked out beforehand for the accomplishment of a goal. It involves the analysis of the desired goal and its division into sub-goals which are subsequently treated in the same way until a set of primitive objectives is obtained. (3) Modeling of Ice Accretion on Aircraft in Glaze Icing Conditions. The work in aircraft icing over the past year has focused on the fundamental aspects of glaze ice accretion, with the goal of improving analytical ice accretion models. Over the past year, studies have been conducted on the generation of surface roughness on accreting ice surfaces with the goal of providing a deterministic surface roughness in the ice accretion models. (4) Cockpit Display of Hazardous Weather Information. Information transfer and display issues associated with the dissemination of hazardous weather warnings are studied in the context of windshear alerts.
The effect of a simulated glaze ice accretion on the aerodynamic performance of a three-dimensional swept wing is studied experimentally. A semispan wing of effective aspect ratio four was mounted from a splitter plate in the OSU subsonic wind tunnel. The model uses a NACA 0012 airfoil section on a rectangular planform with interchangeable tip and root pieces to allow for 0- and 30-degree sweep. Surface pressures were measured at 5 semispan locations on the swept-wing model. The section lift data for the 5 semispan locations are presented and compared with theory and zero-sweep model results. In addition, previously unpublished roughness data from the zero-sweep model is presented here. These data show a large drag and maximum lift penalty due to rough simulated glaze ice. The effect of wing-sweep is seen through a decrease in wing lift performance for both the clean and iced wing.
Tests were conducted at the Icing Research Tunnel at the NASA Lewis Research Center to determine the icing characteristics of three modern airfoils, a natural laminar flow, a medium speed and a swept medium speed airfoil. Tests measured the impingement characteristics and drag degradation for angles of attack typifying cruise and climb for cloud conditions typifying the range that might be encountered in flight. The maximum degradation occurred for the cruise angle of attack for the long glaze ice condition for all three airfoils with increases over baseline drag being 486 percent, 510 percent, and 465 percent for the natural laminar flow, the medium speed and the swept medium speed airfoil respectively. For the climb angle of attack, the maximum drag degradation (and extent of impingement) observed were also for the long glaze ice condition, and were 261 percent, 181 percent and 331 percent respectively. The minimum drag degradation (and extent of impingement) occurred for the cruise condition and for the short, rime spray which increases over baseline drag values of 47 percent, 28 percent and 46 percent respectively.
The study focuses on a deterministic model of the surface roughness transition behavior of glaze ice and analyzes the initial smooth/rough transition location, bead formation, and the propagation of the transition location. Based on a hypothesis that the smooth/rough transition location coincides with the laminar/turbulent boundary-layer transition location, a multizone model is implemented in the LEWICE code. In order to verify the effectiveness of the model, ice accretion predictions for simple cylinders calculated by the multizone LEWICE are compared to experimental ice shapes. The glaze ice shapes are found to be sensitive to the laminar surface roughness and bead thickness parameters controlling the transition location, while the ice shapes are found to be insensitive to the turbulent surface roughness.
Tests were conducted in the Icing Research Tunnel at the NASA Lewis Research Center to determine the icing characteristics of three modern airfoils: a natural-laminar-flow, a medium-speed, and a swept medium-speed airfoil. The tests measured the impingement characteristics and drag degradation for angles-of-attack typifying cruise and climb for cloud conditions typifying the range that might be encountered in flight. The maximum degradation occurred at the cruise angle-of-attack for the long, glaze ice condition for all three airfoils with increases over baseline drag being 486 percent, 510 percent, and 465 percent for the natural-laminar-flow, the medium-speed, and the swept, medium-speed airfoils, respectively. For the climb angle-of-attack, the maximum drag degradation (and total extent of impingement) observed were also for the long, glaze ice condition and were 261 percent, 181 percent, and 331 percent, respectively. The minimum drag degradation (and extent of impingement) occurred for the cruise condition and for the short, rime spray with increases over baseline drag values being 47 percent, 28 percent, 46 percent, respectively.
The focus here is on a deterministic model of the surface roughness transition behavior of glaze ice. The initial smooth/rough transition location, bead formation, and the propagation of the transition location are analyzed. Based on the hypothesis that the smooth/rough transition location coincides with the laminar/turbulent boundary layer transition location, a multizone model is implemented in the LEWICE code. In order to verify the effectiveness of the model, ice accretion predictions for simple cylinders calculated by the multizone LEWICE are compared to experimental ice shapes. The glaze ice shapes are found to be sensitive to the laminar surface roughness and bead thickness parameters controlling the transition location, while the ice shapes are found to be insensitive to the turbulent surface roughness.
Patterns of roughness evolution have been studied analysis of high magnification video observations of accreting ice surfaces provided by the NASA Lewis Research Center. Three distinct patterns of surface roughness generation have been identified within the parametric regions studied. They include: Rime, Multi-Zone Glaze, and Uniform Glaze. Under most icing conditions, a brief period of transient rime ice growth was observed caused by heat conduction into the body. The resulting thin rime layer explains previously observed insensitivity of some ice accretions to substrate insensitivity of some ice accretions to substrate surface chemistry and may provide justification for simplifying assumptions in ice accretion sailing and modeling effects.
A special test apparatus was developed to measure the tensile strength of impact ices perpendicular to the direction of growth. The apparatus consists of a split tube carefully machined to minimize the effect of the joint on impact ice strength. The tube is supported in the wind tunnel by two carefully aligned bearings. During accretion the tube is turned slowly in the icing cloud to form a uniform coating of ice on the split tube specimen. The two halves of the split tube are secured firmly by a longitudinal bolt to prevent relative motion between the two halves during ice accretion and handling. Tensile test strength results for a variety of icing conditions were obtained. Both glaze and rime ice conditions were investigated. In general, the tensile strength of impact ice was significantly less than refrigerator ice. Based on the limited data taken, the median strength of rime ice was less than glaze ice. However, the mean values were similar.
Ice was formed on a full-scale unheated supersonic nose inlet in the NACA Lewis icing tunnel to determine its effect on compressor-face total-pressure distortion and recovery.Inlet angle of attack was varied from 0degrees to 12 degrees, free-stream Mach number from 0.17 to 0.28, and compressor-face Mach number from 0.10 to 0.47. Icing-cloud liquid-water content was varied from 0.65 to 1.8 grams per cubic meter at free-stream static air temperatures of 15 degrees and 0 degrees F. The addition of ice to the inlet components increased total-pressure-distortion levels and decreased recovery values compared withclear0air results, the losses increasing with time in ice. The combination of glaze ice, high corrected weight flow, and high angle of attack yielded the highest levels of distortion and lowest values of recovery. The general character of compressor-face distortion with an iced inlet was the same as that for the clean inlet, the total-pressure gradients being predominantly radial, with circumferential gradients occurring at angle of attack. At zero angle of attack, free-stream Mach number of 0.27, and a constant corrected weight flow of 150 pounds per second (compressor-face Mach number of 0.43), compressor-face total-pressure-distortion level increased from about 6 percent in clear air to 12 percent after 21 minutes of heavy glaze icing; concurrently, total-pressure recovery decreased from about 0.98 to 0.945. For the same operating conditions but with the inlet at 12 deg angle of attack, a change in distortion level occurred from about 9 percent in clear air to 14 percent after 2-1/4 minutes of icing, with a decrease in recovery from about 0.97 to 0.94.