Rotor Experiment Research Articles

Interpretation of Mössbauer experiment in a rotating system: A new proof for general relativity

A historical experiment by Kündig on the transverse Doppler shift in a rotating system measured with the Mössbauer effect (Mössbauer rotor experiment) has been recently first re-analyzed and then replied by an experimental research group. The results of re-analyzing the experiment have shown that a correct re-processing of Kündig’s experimental data gives an interesting deviation of a relative redshift between emission and absorption resonant lines from the standard prediction based on the relativistic dilatation of time. That prediction gives a redshift ∇EE≃−12v2c2 where v is the tangential velocity of the absorber of resonant radiation, c is the velocity of light in vacuum and the result is given to the accuracy of first-order in v2c2. Data re-processing gave ∇EE≃−kv2c2 with k=0.596±0.006. Subsequent new experimental results by the reply of Kündig experiment have shown a redshift with k=0.68±0.03 instead.By using Einstein Equivalence Principle, which states the equivalence between the gravitational “force” and the pseudo-force experienced by an observer in a non-inertial frame of reference (included a rotating frame of reference) here we re-analyze the theoretical framework of Mössbauer rotor experiments directly in the rotating frame of reference by using a general relativistic treatment. It will be shown that previous analyses missed an important effect of clock synchronization and that the correct general relativistic prevision in the rotating frame gives k≃23 in perfect agreement with the new experimental results. Such an effect of clock synchronization has been missed in various papers in the literature with some subsequent claim of invalidity of relativity theory and/or some attempts to explain the experimental results through “exotic” effects. Our general relativistic interpretation shows, instead, that the new experimental results of the Mössbauer rotor experiment are a new, strong and independent, proof of Einstein general relativity.In the final section of the paper we discuss an analogy with the use of General Relativity in Global Positioning Systems.

Study on the recognition of aero-engine blade-casing rubbing fault based on the casing vibration acceleration

By mean of the aero-engine rotor experiment rig with casings, the blade-casing rubbing experiments, which include the single-point rubbing and the partial rubbing, are carried out. The casing vibration acceleration signals are analyzed in order to extract the rubbing faults’ characteristics. The results show that: the casing signals under rubbing have obvious impact characteristics; the impact frequency is the frequency of blades passing the casing, and it equals the product of rotating frequency and the number of blades; in the frequency spectrum, there is the blades-passing frequency and its multiple-frequencies; the strength of impact is modulated by rotating frequency, so that there are families of side bands on both sides of the blades-passing frequency and its multiple frequencies, and the side bands’ interval equals the rotating frequency. There are obvious quefrency components of the rotating frequency and its multiple frequencies in the cepstrum. Finally, the rubbing characteristics found out in this paper are verified by using an actual aero-engines’ test data.

Determination of non‐stationarity in the surface layer during the T‐REX experiment

Stationarity is a fundamental assumption in the statistical investigation of turbulence and the development of similarity functions that are widely used in surface‐layer parametrization schemes. Non‐stationary time series should therefore be removed from the analysis before assessing turbulence statistics used in similarity functions. Many approaches have been developed over the years to determine non‐stationarity of means and (co‐)variances, but there has been no systematic investigation of the differences and similarities between the approaches. In this article, we contrast several frequently used approaches, including two statistical tests to determine trends, the determination of a non‐stationarity ratio, and the determination of differences in turbulence statistics calculated for different averaging times. We apply these approaches to near‐surface time series of wind and temperature collected during the Terrain‐induced Rotor Experiment (T‐REX). Our results show that the degree of non‐stationarity varies considerably with the approach used. Investigation of the time series that are declared stationary by all the above approaches simultaneously reveals that in many cases such time series still show a behaviour indicative of intermittent turbulence, both for stable and unstable conditions. When these approaches are combined with an additional condition for the intermittency level, a rigorous approach for the detection of non‐stationarity is developed.

A novel method for identifying rotor-stator rubbing positions using the cepstrum analysis technique

A novel method of aero-engine rubbing positions identification based on cepstrum analysis is proposed, and the transfer path characteristics which reflect the transfer characteristics information from rubbing points to casing measuring points are separated from the vibration acceleration signals of casing by means of cepstrum analysis. Therefore, there is different transfer characteristics information at different rubbing positions, and in view of this, twenty rubbing positions identification features from the cepstrum are extracted. A large number of rubbing experiments of different positions are simulated with the rotor experiment rig of aero-engine, and the characteristic analysis of experimental samples at different rubbing positions is carried out, and the results indicate the consistency of features to the same rubbing position and the difference of the features to the different rubbing positions. Finally, the aero-engine rubbing positions identification is carried out using the nearest neighbor classification method, the recognition rate reaches 100%, and the effectiveness of the method is full verified.

Identifying Rotor-stator Rubbing Positions Using the Cepstrum Analysis Technique

The method of aero-engine rubbing positions identification based on cepstrum analysis is proposed. The transfer path characteristics which reflect the transfer characteristics information from rubbing points to casing measuring points are separated from the vibration acceleration signals of casing by means of cepstrum analysis. Therefore, there is different transfer characteristics information at different rubbing positions, and in view of this, twenty rubbing positions identification features are extracted. A large number of rubbing experiments of different positions are simulated with the rotor experiment rig of aero-engine, and the characteristic analysis of experimental samples at different rubbing positions is carried out, and the results indicate the consistency of features to the same rubbing position and the difference of the features to the different rubbing positions. Aero-engine rubbing positions identification is carried out using the nearest neighbor classification method. The recognition rate reaches 100%, and the effectiveness of the method is full verified.

Nighttime Turbulent Events in a Steep Valley: A Nested Large-Eddy Simulation Study

Abstract This numerical study investigates the nighttime flow dynamics in Owens Valley, California. Nested high-resolution large-eddy simulation (LES) is used to resolve stable boundary layer flows within the valley. On 17 April during the 2006 Terrain-Induced Rotor Experiment, the valley atmosphere experiences weak synoptic forcings and is largely dominated by buoyancy-driven downslope and down-valley flows. Tower instruments on the valley floor record a continuous decrease in temperature after sunset, except for a brief warming episode. This transient warming event is modeled with good magnitude and temporal precision with LES. Analysis of the LES flow field confirms the event to be the result of a slope to valley flow transition, as previously suggested by researchers based on field observations. On the same night, a northerly cold airflow from the Great Basin is channeled through a pass on the eastern valley sidewall. The current plunges into the stable valley atmosphere, overshooting the altitude of its neutral buoyancy, and generating a large-scale oscillatory motion. The resulting cross-valley flow creates strong vertical shear with the down-valley flow in the lower layers of the atmosphere. A portion of the cross-valley flow is captured by a scanning lidar. The nested LES is in good agreement with the lidar-recorded radial velocity. Furthermore, the LES is able to resolve Kelvin–Helmholtz waves, and ejection and sweep events at the two-layer interface, which lead to top-down vertical mixing.

High-Resolution Doppler Lidar Observations of Transient Downslope Flows and Rotors

Abstract The authors present observations of the temporal evolution of downslope windstorms with rotors and internal hydraulic jumps of unprecedented detail and spatiotemporal coverage. The observations were carried out by means of a coherent Doppler lidar in the lee of the southern Sierra Nevada range during the sixth intensive observational period of the Terrain-induced Rotor Experiment (T-REX) in 2006. Two representative flow regimes are analyzed and juxtaposed in this paper. The first case shows pulses of high-momentum air that propagate eastward through the valley with an internal hydraulic jump on the leading edge. The region downstream of the transient internal hydraulic jump is characterized by turbulence but no coherent rotor circulation was observed. During the second case, the strongest windstorm of the field campaign T-REX occurred. The observed features of this event resemble the classical notion of a rotor. Altogether, the Doppler lidar observations of both downslope flow events reveal a complex, turbulent flow that is highly transient, intermittent, 3D, and interacts with a significant along-valley flow.

A down-valley low-level jet event during T-REX 2006

A prolonged down-valley flow and low-level jet were observed throughout the Enhanced Observing Period 4 (April 28–29) of the 2006 Terrain-induced Rotor Experiment, held in the Owens Valley of California near the town of Independence. The low-level jet was strongest during the nocturnal hours, and special field observations captured important details of the event lifecycle. High-resolution simulations using the Weather Research and Forecasting numerical weather prediction model were generated, with underlying assumptions being that model resolution, boundary layer physics, and nesting configuration would be dominant controlling factors in reproducing the jet. The large-scale conditions were dry throughout the event, so moist physics were not a significant forcing consideration. For the control simulation, a two-nest (4.5 and 1.5 km grid spacing) configuration with 90 vertical levels was applied. Additionally, the Quasi-Normal Scale Elimination planetary boundary and surface layer option were selected due to its published performance under conditions of stable stratification. Three other sensitivity simulations were run for comparison, differing from the control just in the choice of vertical resolution (60 versus 90 levels with Quasi-Normal Scale Elimination) and planetary boundary/surface layer physics (90 levels/Mellor-Yamada-Jancic; 90 levels/Yonsei State University). Although the gross evolution (location, height, and timing) of the low-level jet is captured by all model runs (with the 1.5 km inner nest providing the more accurate details), there were at times large underestimations of the nocturnal jet speed max in each simulation (approaching 100 % error, or up to almost 10 m s−1). Overall, the variations of vertical resolution and planetary boundary/surface physics against the control seemed to (1) yield little overall improvement to statistical or subjective evaluations; (2) do little to improve deficiencies in reproducing the magnitude strength of the nocturnal down-valley low-level jet. Since the cold-start simulations spanned 36 h (including a 12-h spin-up period), it was suspected that the lateral boundary conditions imposed on the outermost 4.5 km nest might negatively impact the interior model solutions in the Owens Valley. To investigate this possibility, an additional simulation was executed by adding two extra nests to the control configuration: an outer 13.5 km and an inner 500 m. This simulation produced a better evolution of the nocturnal low-level jet and especially the speed max. The addition of the larger 13.5 km nest appears more critical to this improvement than that of the extra spatial resolution provided by the inner 500 m nest, which supports the idea that accurate capturing of the large-scale synoptic condition was critical in reproducing important details of this down-valley low-level jet event. The extra 500-m resolution did seem to improve the morning valley cold pool forecast.

Cerebellar Morphology and Procedural Learning Impairment in Neuroleptic-Naive Youth at Ultrahigh Risk of Psychosis.

Despite evidence suggesting a role for cerebellar abnormalities in the pathogenesis of psychosis, the structure has yet to receive attention in individuals at ultrahigh risk for psychosis (UHR). Accumulating research has suggested that the cerebellum helps modulate cognition and movement, domains in which UHR individuals show impairment; understanding putative markers of risk, such as structural abnormalities and behavioral correlates, is essential. In this study, participants underwent a high-resolution structural brain scan and participated in a pursuit rotor experiment. Cerebellar regions associated with movement (anterior cerebellum) and cognition (crus I) were subsequently analyzed. UHR participants showed impaired performance on the pursuit rotor task, learned at a slower rate, and showed smaller cerebellar volumes compared with control participants. Left crus I volume was significantly associated with poor rate of learning. The present results suggest that cerebellar abnormalities and their behavioral correlates (poor learning and motor control) precede the onset of psychosis.

Evaluating Reynolds number effects in small-scale wind turbine experiments

A series of experiments was conducted to evaluate the effect of the Reynolds number on the initial wake expansion and on the thrust coefficient in scaled wind turbine tests. Two scaled horizontal axis wind turbines were tested in a 0.6m×0.8m closed-loop water channel at Reynolds numbers that ranged from 3620 to 31,400, based on the blade tip speed and tip chord. The first rotor was a three-bladed rotor custom-designed to operate in these low Reynolds number conditions. The second rotor was a 1/4.8 scaled model of an existing two-bladed rotor. The initial wake expansion was assessed by using quantitative dye visualisation to identify the propagation of tip vortices downstream of the rotor. Thrust coefficients were determined from data obtained with a six degree-of-freedom balance. Dye visualisation indicated that the initial wake expansion downstream of the custom three-bladed rotor narrowed when the Reynolds number was lower than 20,000. Additional experiments compared the wake expansion downstream of the scaled two-bladed rotor to existing data recorded for a medium-scale rotor. The wake in the scaled two-bladed rotor was 30–60% narrower than the medium-scale rotor′s wake depending on the Reynolds number. Similarly, the thrust coefficient was reduced by 25–60% in the scaled two-bladed rotor experiments as a result of lower Reynolds numbers than in the medium-scale experiment. The results have identified that the thrust coefficient of a geometrically-scaled rotor may be degraded in a low Reynolds number environment whereas a rotor designed for the particular Reynolds number regime can generate thrust coefficients that are representative of commercial-scale wind turbines.

CFD predictions of NREL Phase VI Rotor Experiments in NASA/AMES Wind tunnel

This article presents the computational predictions of NREL Phase VI rotor, a stall-regulated two bladed wind turbine with full-span pitch control and a power rating of 20 kW, in the NASA/AMES 80 ft. X 120 ft. wind tunnel. A 3D CFD–RANS approach is used, modeling single blade of the rotor utilizing periodicity, in a rotating frame of reference; over several upwind cases. All the simulations are performed using the commercial multi-purpose CFD solver ANSYS CFX 12.1. The blade is modeled with simplified spherical hub excluding nacelle and tower, at stationary wind conditions neglecting wall shear effects due to tunnel blockage. The comparisons are done for the blade with 0° yaw angle and 3° tip pitch angle. Reasonably good agreement is obtained when comparing modeled mechanical effects Viz. power, thrust, and span wise force components with measurements over wind speeds ranging from 5m/s to 25m/s. The capability of CFD in predicting complex 3D wind turbine aerodynamics is demonstrated in this paper with NREL Phase VI data campaign as a case study.

A New Similarity Measure of Generalized Trapezoidal Fuzzy Numbers and Its Application on Rotor Fault Diagnosis

Fault diagnosis technology plays a vital role in the variety of critical engineering applications. Fuzzy approach is widely employed to cope with decision-making problems because it is in the simplest and most used form. This paper proposed a new similarity measure of generalized trapezoidal fuzzy numbers used for fault diagnosis. The presented similarity measure combines concepts of the geometric distance, the center of gravity point, the perimeter, and the area of the generalized trapezoidal fuzzy numbers for calculating the degree of similarity between generalized trapezoidal fuzzy numbers. This method is proposed to deal with both standardized and nonstandardized generalized trapezoidal fuzzy numbers. Some properties of the proposed similarity measure have been proved, and 12 sets of generalized fuzzy numbers have been used to compare the calculation results of the proposed similarity measures with the existing similarity measures. Comparison results indicate that the proposed similarity measure can overcome the drawbacks of existing similarity measures. Finally, a fault diagnosis experiment is carried out in laboratory based on multifunctional flexible rotor experiment bench. Experimental results demonstrate that the proposed similarity measure is more effective than other methods in terms of rotor fault diagnosis.

Isobaric Height Perturbations Associated with Mountain Waves Measured by Aircraft during the Terrain-Induced Rotor Experiment

Abstract It has only been in the last few years that accurate measurement of the horizontal pressure gradient has been possible over complex terrain using an airborne platform. To infer forcing mechanisms for the wind, an independent measure of the height of an isobaric surface is required. Differential GPS analyses have enabled determination of the aircraft height with sufficient accuracy to infer isobaric heights. When coupled with an accurate measurement of static pressure, the horizontal pressure field can be determined. To demonstrate this measurement technique, research flight legs by the University of Wyoming King Air (UWKA) conducted in support of the Terrain-Induced Rotor Experiment (T-REX) in March and April 2006 are examined. UWKA flights conducted on 14 and 25 March and 16 April 2006 encountered strong mountain waves in response to winds directed primarily normal to the Sierra Nevada ridgeline. Winds at flight level showed pronounced variation that suggested topographic influence. The magnitude of isobaric height perturbations along UWKA flight tracks obtained using differential GPS during case study days of 14 and 25 March and 16 April are shown to exceed 70 m, corresponding to horizontal pressure perturbations greater than 4 hPa. Measurements suggest that changes in wind speed are linked primarily to the perturbation height field and that the flow can be classified as Eulerian, implying that Coriolis accelerations are negligible and flows respond to the horizontal pressure gradient force.

Analysis on Oil Whip of Steam Turbine

Oil whip, which is one of the typical types of steam turbine failure, may lead to large amplitude vibration of the rotor and even to catastrophic accident. In order to prevent and on-line eliminate the oil whip, researches on vibration of steam turbine caused by the oil whip and its characteristics have been elaborated from two respects of theory and experiment. The causes and the formation mechanism of the oil whip have been analyzed, and in certain conditions, a series of experiments for the oil whip on the rotor experiment rig have been made. Illustrating and summarizing the results of these experiments by change the rotor speed and the lubricant quantity. These researches on the oil whip could provide some theoretical bases for the practical work. Along with the expounded prevention measures of oil whip, some ideas on oil whip online elimination are put forward.

Rotor dynamics analysis and experiment study of the flywheel spin test system

The strength study of the flywheel is important to the flywheel energy storage. The motor and bearing are the key challenges for the high-speed flywheel spin test device in vacuum. By using a small stiffness pivot-jewel bearing and a spring squeeze film damper as the lower support of the flywheel, a simple spin system was designed at a low cost and is suitable for longtime operation. The auxiliary sup- port at the top was not removed until the flywheel passed the first critical speed. The flywheel that kept its rigid state in sub-critical state was tested at the high speed without the top support. The dynamic model of the flywheel-bearing-damper was built by means of the La- grangian equation to calculate critical speeds, mode shapes and modal damping ratios at different speeds. The lower damper's effects on the modal damping ratios and forced vibration were discussed. The vibrations of the flywheel-bearing-damper system were measured at the different damping coefficients in the experiment. When the lower damper was adjusted to be overdamped, the flywheel ran up to 50000 r/min steadily, and the experimental result was in agreement with the theoretical assumption. The sub-critical rotor dynamics de- sign and pivot-jewel bearing proved to be good solutions to the spin test for the composite flywheel.

High-Resolution Simulations of Lee Waves and Downslope Winds over the Sierra Nevada during T-REX IOP 6

AbstractThe downslope windstorm during intensive observation period (IOP) 6 was the most severe that was detected during the Terrain-Induced Rotor Experiment (T-REX) in Owens Valley in the Sierra Nevada of California. Cross sections of vertical motion in the form of a composite constructed from aircraft data spanning the depth of the troposphere are used to link the winds experienced at the surface to the changing structure of the mountain-wave field aloft. Detailed analysis of other observations allows the role played by a passing occluded front, associated with the rapid intensification (and subsequent cessation) of the windstorm, to be studied. High-resolution, nested modeling using the Met Office Unified Model (MetUM) is used to study qualitative aspects of the flow and the influence of the front, and this modeling suggests that accurate forecasting of the timing and position of both the front and strong mountaintop winds is crucial to capture the wave dynamics and accompanying windstorm. Meanwhile, far ahead of the front, simulated downslope winds are shallow and foehnlike, driven by the thermal contrast between the upstream and valley air mass. The study also highlights the difficulties of capturing the detailed interaction of weather systems with large and complex orography in numerical weather prediction.

Fluctuation Theorems for an Asymmetric Rotor in a Granular Gas

We investigate the validity of fluctuation theorems for an asymmetric rotor experiment in a granular gas. A first state, with a Gaussian distribution of the angular velocity, is found to be well described by a first order Langevin equation. We show that fluctuation theorems are valid for the injected work and for the total entropy production. In a second state, the angular velocity distribution is double peaked due to a spontaneous symmetry breaking: A convection roll develops in the granular gas, which strongly couples to the rotor. Surprisingly, in this case, similar symmetry relations hold, which lead to a good prediction for the height ratio of the two peaks.

Investigation of a Complex Nocturnal Flow in Owens Valley, California Using Coherent Doppler Lidar

A study of an interesting meteorological episode over the Owens Valley, California, USA during the Terrain-Induced Rotor EXperiment was conducted using a recently adapted statistical interpolation method to retrieve wind-velocity vectors from Doppler lidar data. This vector retrieval method has been adapted from radar data assimilation techniques. Results show that the method allows better preservation of local variations in the flow field than other techniques. In addition, a high resolution Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) run is used to understand the large-scale flow within the valley and compared with lidar retrievals. Observations from 1030 UTC to 1230 UTC (0230 local time to 0430 local time) on March 27, 2006 are presented. Lidar observations show complex and uncharacteristic flows such as sudden bursts of westerly cross-valley wind mixing with the dominant up-valley wind. Model results from COAMPS and other in-situ instrumentation are used to corroborate and complement these observations. The optimal interpolation technique for Doppler lidar data vector retrieval appears well suited for scenarios with complex spatial variations in the flow field.

Validation of the Beddoes–Leishman dynamic stall model for horizontal axis wind turbines using MEXICO data

ABSTRACTThe aim of this study is to assess the load predicting capability of a classical Beddoes–Leishman dynamic stall model in a horizontal axis wind turbine environment, in the presence of yaw misalignment. The dynamic stall model was tailored to the horizontal axis wind turbine environment and validated against unsteady thick airfoil data. Subsequently, the dynamic stall model was implemented in a blade element‐momentum code for yawed flow, and the results were compared with aerodynamic measurements obtained in the MEXICO (Model Rotor Experiments under Controlled Conditions) project on a wind turbine rotor placed in a large scale wind tunnel. In general, reasonable to good agreement was found between the blade element‐momentum model and MEXICO data. When large yaw misalignments were imposed, poor agreement was found in the downstroke of the movement between the model and the experiment. Still, over a revolution, the maximum normal force coefficient predicted was always within 8% of experimental data at the inboard stations, which is encouraging especially when blade fatigue calculations are being considered. Copyright © 2012 John Wiley & Sons, Ltd.

Balancing of flexible rotors without trial weights based on finite element modal analysis

With the continuous improvement of aviation engine performance, the engine rotor’s working speed is above the first critical speed, and some small engine rotor’s operating speed exceeds the second critical speed, thus most of the aircraft engine rotor is now flexible rotor. The primary goal of this research is to provide a new method without trial weights for flexible rotor balancing, which is based on the traditional modal balancing method and combines the dynamic characteristics of the rotor, such as the model shape, obtained by using finite element analysis software, the critical speed, the modal damping ratio, and so on. To demonstrate the validity and accuracy of the new method, two experiments are carried out. One is on a four-disk simply supported structure rotor experiment, which is balanced by using three balancing planes. After balancing the amplitude of the rotor through the first critical speed is reduced 80%. The other is on a turboshaft engine power turbine rotor which had been balanced quite well. The initial amplitude of the turboshaft engine power turbine rotor is 0.05 mm when it rotates at low speed, and the maximum amplitude is just 0.12 mm when it rotates at the first critical speed. After balancing the amplitude of the rotor through the first critical speed is reduced to 0.06 mm. The results of the experiments indicate that the new without trial weights method is a significant effective method for the flexible rotor dynamic balancing, and it will be widely used to balance the engine rotor.