Results of a sub-scale model rotor icing test

A heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA Lewis Research Center Icing Research Tunnel (IRT) in September and November 1989. The four-bladed main rotor had a diameter of 1.83 m (6.00 ft) and the 0.124 m (4.9 in) chord rotor blades were specially fabricated for this experiment. The instrumented rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The model rotor was exposed to a range of icing conditions that included variations in temperature, liquid water content, and median droplet diameter, and was operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed) and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracings, and ice molds. The sensitivity of the model rotor to the test parameters, is given, and the result to theoretical predictions are compared. Test data quality was excellent, and ice accretion prediction methods and rotor performance prediction methods (using published icing lift and drag relationships) reproduced the performance trends observed in the test. Adjustments to the correlation coefficients to improve the level of correlation are suggested

Model rotor icing tests in the NASA Lewis icing research tunnel

Tests of a lightly instrumented two-bladed teetering rotor and a heavily instrumented sub-scale articulated main rotor were conducted in the NASA Lewis Research Center Icing Research Tunnel (IRT) in August 1988 and September and November 1989. The first was an OH-58 tail rotor which had a diameter of 1.575 m and a blade chord of 0.133 m, and was mounted on a NASA designed test rig. The second, a four bladed articulated rotor, had a diameter of 1.83 m with 0.124 m chord blades specially fabricated for the experiment. This rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The models were exposed to variations in temperature, liquid water content, and medium droplet diameter, and were operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed), and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracing, and ice molds. Presented here are the sensitivity of the model rotors to the test parameters and a comparison of the results to theoretical predictions

An overview of a model rotor icing test in the NASA Lewis Icing Research Tunnel

During two entries in late 1989, a heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA LeRC Icing Research Tunnel (IRT). The results of this series of tunnel tests were published previously. After studying the results from the 1989 test and comparing them to predictions, it became clear that certain test conditions still needed investigation. Therefore, a re-entry of the Sikorsky Aircraft Powered Force Model (PFM) in the IRT was instituted in order to expand upon the current rotor craft sub-scale model experimental database. The major areas of interest included expansion of the test matrix to include a larger number of points in the FAA AC 29-2 icing envelope, inclusion of a number of high power rotor performance points, close examination of warm temperature operations, operation of the model in constant lift mode, and testing for conditions for icing test points in the full scale helicopter database. The expanded database will allow further and more detailed examination and comparison with analytical models. Participants in the test were NASA LeRC, the U.S. Army Vehicle Propulsion Directorate based at LeRC, and Sikorsky Aircraft. The model rotor was exposed to a range of icing conditions (temperature, liquid water content, median droplet diameter) and was operated over ranges of shaft angle, rotor tip speed, advance ratio, and rotor lift. The data taken included blade strain gage and balance data, as well as still photography, video, ice profile tracings, and ice molds. A discussion of the details of the test is given herein. Also, a brief examination of a subset of the data taken is also given

Role of Wind Tunnels and Computer Codes in the Certification and Qualification of Rotorcraft for Flight in Forecast Icing

The cost and time to certify or qualify a rotorcraft for flight in forecast icing has been a major impediment to the development of ice protection systems for helicopter rotors. Development and flight test programs for those aircraft that have achieved certification or qualification for flight in icing conditions have taken many years, and the costs have been very high. NASA, Sikorsky, and others have been conducting research into alternative means for providing information for the development of ice protection systems, and subsequent flight testing to substantiate the air-worthiness of a rotor ice protection system. Model rotor icing tests conducted in 1989 and 1993 have provided a data base for correlation of codes, and for the validation of wind tunnel icing test techniques. This paper summarizes this research, showing test and correlation trends as functions of cloud liquid water content, rotor lift, flight speed, and ambient temperature. Molds were made of several of the ice formations on the rotor blades. These molds were used to form simulated ice on the rotor blades, and the blades were then tested in a wind tunnel to determine flight performance characteristics. These simulated-ice rotor performance tests are discussed in the paper. The levels of correlation achieved and the role of these tools (codes and wind tunnel tests) in flight test planning, testing, and extension of flight data to the limits of the icing envelope are discussed. The potential application of simulated ice, the NASA LEWICE computer, the Sikorsky Generalized Rotor Performance aerodynamic computer code, and NASA Icing Research Tunnel rotor tests in a rotorcraft certification or qualification program are also discussed. The correlation of these computer codes with tunnel test data is presented, and a procedure or process to use these methods as part of a certification or qualification program is introduced

Separation of Excitation Forces from Simulated Gas Turbine Casing Response Measurements

Condition monitoring of blades within gas turbines has been and will continue to be of importance in all areas of their use, for maintenance and reliability purposes. Non-intrusive measurement of blade condition is the ambition of most techniques for this endeavour, with a number of methods proposed, investigated and employed for such measurement, with the current dominant method using proximity probes to measure blade arrival time for subsequent processing. It is proposed, however, that the measurement of the casing vibration, due to the aerodynamic-structural interaction within a gas turbine, could provide a means of blade condition monitoring and modal parameter estimation, without requiring perforation of the casing. An analytical model of a gas turbine casing and simulated pressure signal associated with the rotating blades, individual blade vibrations and transfer of stator blade vibrations has been developed in order to understand the complex relationship between casing response and the most important excitation forces. Due to the force interaction being through a fluid medium, a certain degree of randomness is introduced into the excitations, and the viability of this inherent randomness as a useful aid for separation of the contributing excitation forces from the system response is explored

Monitoring based on time-frequency tracking of estimated harmonic series and modulation sidebands

International audienceThe installation of a Condition Monitoring System (CMS) on a mechanical machine (e.g., on a wind turbine) aims to reduce the operating costs by applying a predictive maintenance strategy. The CMS is composed of sensors acquiring signals from which system health indicators are computed and monitored. Part of those indicators are predefined depending on the monitored system kinematic and are computed by averaging large or narrow spectral bands. The averaging and the need for predefined thresholds for default detection may induce lots of false alarms while reducing the ability to detect the default early. To get precise health indicators reflecting each local meaningful spectral content, the AStrion software proposes a new data-driven monitoring strategy without any a priori on the measured signals. First, an automatic spectral analysis is applied to detect, characterize and classify the different spectral structures of the successive measured signals. These spectral structures can be either single spectral peaks, either peaks grouped in harmonic series or in modulation sidebands [1]. Second, these spectral structures are characterized by several features, including for example the number of peaks, the characteristic frequencies and the energy. This gives a snapshot of the system health at the signal acquisition time. To perform an automatic diagnosis of the system, the spectral evolution should be tracked along the time snapshots. In this paper, we propose a time tracking method based on McAulay & Quatieri algorithm [2] which has been designed originally for speech signals acquired on a continuous temporal basis. We have adapted [2] in order to account not only for single spectral peak evolution but also for the evolution of more complex structures such as harmonic series or modulation sidebands, even in the case of signals acquired on a non-regular temporal basis, as it is often the case. Moreover, an added sleep state makes the proposed method robust against nondetected spectral structures at a given time. Finally, the temporal evolution of the spectral structure features can be monitored and used as precise health indicators. The following figure is a result of the proposed method applied on real signals coming from a test bench designed in KAStrion project for simulating a wind turbine operation and for which the inner race of the main bearing has been damaged. Above, the time frequency map displays a zoom of the spectral peaks detected (around 20.000 per snapshot, represented by circles) and shows in blue the tracking from 44 to 189 operating hours of a spectral peak at 3.45 Hz. This particular peak evolves at 129 hours to become an harmonic series with more and more peaks and energy. Its energy evolution (plotted below) shows an increase which mirrors out a failure. In a following step [3], this spectral structure has been associated with the ball pass frequency of the inner ring of the main bearing. A dismantling of this bearing has confirmed the failure. This result shows the potential of the proposed data-driven method to create automatically relevant health indicators

Probing Unstable Massive Neutrinos with Current Cosmic Microwave Background Observations

The pattern of anisotropies in the Cosmic Microwave Background depends upon the masses and lifetimes of the three neutrino species. A neutrino species of mass greater than 10 eV with lifetime between 10^{13} sec and 10^{17} sec leaves a very distinct signature (due to the integrated Sachs-Wolfe effect): the anisotropies at large angles are predicted to be comparable to those on degree scales. Present data exclude such a possibility and hence this region of parameter space. For $m_\nu \simeq 30$ eV, $\tau \simeq 10^{13}$ sec, we find an interesting possibility: the Integrated Sachs Wolfe peak produced by the decaying neutrino in low-$\Omega$ models mimics the acoustic peak expected in an $\Omega = 1$ model.Comment: 5 pages, 4 figure