摘要 :
A rotor system (4) having odd and even blade assemblies (O.sub.b, E.sub.b) mounting to and rotating with a rotor hub assembly (6) wherein the odd blade assemblies (O.sub.b) define a radial length R.sub.O, and the even blade assemb...
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A rotor system (4) having odd and even blade assemblies (O.sub.b, E.sub.b) mounting to and rotating with a rotor hub assembly (6) wherein the odd blade assemblies (O.sub.b) define a radial length R.sub.O, and the even blade assemblies (E.sub.b) define a radial length R.sub.E and wherein the radial length R.sub.E is between about 70 to about 95 of the radial length R.sub.O. Other embodiments of the invention are directed to a Variable Diameter Rotor system (4) which may be configured for operating in various operating modes for optimizing aerodynamic and acoustic performance. The Variable Diameter Rotor system (4) includes odd and even blade assemblies (O.sub.b, E.sub.b) having inboard and outboard blade sections (10, 12) wherein the outboard blade sections (12) telescopically mount to the inboard blade sections (10). The outboard blade sections (12) are positioned with respect to the inboard blade sections (10 such that the radial length R.sub.E of the even blade assemblies (E.sub.b) is equal to the radial length R.sub.O of the odd blade assemblies (O.sub.b) in a first operating mode, and such that the radial length R.sub.E is between about 70 to about 95 of the length R.sub.O in a second operating mode.
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摘要 :
An experimental investigation of the effect of tip-shape modification on blade-vortex interaction induced helicopter blade-slap noise has been conducted. The general rotor model system (GRMS) with a 3.148-m (10.33-ft) diameter, fo...
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An experimental investigation of the effect of tip-shape modification on blade-vortex interaction induced helicopter blade-slap noise has been conducted. The general rotor model system (GRMS) with a 3.148-m (10.33-ft) diameter, four-bladed, fully articulated rotor was installed in the Langley Research Center V/STOL tunnel. Tests were conducted over a range of simulated flight and descent velocities which have been shown to produce blade slap. Aerodynamic performance parameters of the rotor system were monitored to ensure properly matched flight conditions among the tip shapes. The tunnel was operated in the open-throat configuration with treatment to improve the acoustic characteris¬tics of the test chamber. Four promising tips (based on previous investiga¬tions) were used (ogee, subwing, 60° swept tapered, and end plate), along with a standard square tip as a baseline configuration. This investigation pro¬vided a detailed acoustic evaluation on the same rotor system of the relative applicability of the various tip configurations for blade-slap noise reduction. (This report applies to the evaluation changes in tip shape on the rotor per¬formance and acoustic signature.)
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A 1/17-scale research model of the AH-1 series helicopter main rotor was tested. Model-rotor acoustic and simultaneous blade pressure data were recorded at high speeds where full-scale helicopter high-speed impulsive noise levels ...
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A 1/17-scale research model of the AH-1 series helicopter main rotor was tested. Model-rotor acoustic and simultaneous blade pressure data were recorded at high speeds where full-scale helicopter high-speed impulsive noise levels are known to be dominant. Model-rotor measurements of the peak acoustic pressure levels, waveform shapes, and directively patterns are directly compared with full-scale investigations, using an equivalent in-flight technique. Model acoustic data are shown to scale remarkably well in shape and in amplitude with full-scale results. Model rotor-blade pressures are presented for rotor operating conditions both with and without shock-like discontinuities in the radiated acoustic waveform. Acoustically, both model and full-scale measurements support current evidence that above certain high subsonic advancing-tip Mach numbers, local shock waves that exist on the rotor blades ""delocalize'' and radiate to the acoustic far-field.
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摘要 :
A 1/17-scale research model of the AH-1 series helicopter main rotor was tested. Model-rotor acoustic and simultaneous blade pressure data were recorded at high speeds where full-scale helicopter high-speed impulsive noise levels ...
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A 1/17-scale research model of the AH-1 series helicopter main rotor was tested. Model-rotor acoustic and simultaneous blade pressure data were recorded at high speeds where full-scale helicopter high-speed impulsive noise levels are known to be dominant. Model-rotor measurements of the peak acoustic pressure levels, waveform shapes, and directively patterns are directly compared with full-scale investigations, using an equivalent in-flight technique. Model acoustic data are shown to scale remarkably well in shape and in amplitude with full-scale results. Model rotor-blade pressures are presented for rotor operating conditions both with and without shock-like discontinuities in the radiated acoustic waveform. Acoustically, both model and full-scale measurements support current evidence that above certain high subsonic advancing-tip Mach numbers, local shock waves that exist on the rotor blades 'delocalize' and radiate to the acoustic far-field.
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摘要 :
A study to identify and control helicopter rotor blade-vortex interaction (BVI) noise and vibratory hub loads using neural networks has been initiated at Ames Research Center. BVI noise can make a major contribution to the total r...
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A study to identify and control helicopter rotor blade-vortex interaction (BVI) noise and vibratory hub loads using neural networks has been initiated at Ames Research Center. BVI noise can make a major contribution to the total rotorcraft noise, and can be annoying. The vibratory hub loads substantially determine the total rotorcraft vibration level. This vibration affects pilot and passenger comfort and the vehicle s structural fatigue life. Current neural control simulation covers simultaneous control of BVI noise and vibratory hub loads by using an objective function approach. In the present study, the advancing side BVI noise and the vibratory hub load components were represented by two metrics, namely, the noise metric and the hub loads metric. The objective function was composed of the sum of the weighted squares of the noise and hub loads metrics. The closed-loop controller must be fast-executing and must converge quickly (in six iterations or less); gradient-based methods must not be used. was completed; it involved the use of a two-hidden-layer radial-basis function neural network with one input and two outputs. A simple, easy-to-implement neural control technique, the 'direct inverse' method, was successfully applied and found to be robust. The present approach had the following essential ingredients: accurate plant modeling, halving of the metric in order to accelerate controller convergence, 'inverted-axes' control modeling, and a feedback iterative loop. A simple, two-hidden-layer back-propagation neural network used in the control step was successful. Results from the present, closed-loop neural network controller showed that simultaneous reductions of 5 decibels in the baseline noise and 54 in the baseline vibratory hub loads were achievable in only two controller iterations.
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The effectiveness of the EPNL procedure in quantifying helicopter blade slap and tail rotor noise heard on approach some distance from the flyover position is addressed. Alternative methods of rating helicopter noise are reviewed ...
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The effectiveness of the EPNL procedure in quantifying helicopter blade slap and tail rotor noise heard on approach some distance from the flyover position is addressed. Alternative methods of rating helicopter noise are reviewed including correction procedures to the EPNL concept which account for blade slap and tail rotor noise. The impact of the use of such corrections is examined.
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摘要 :
When a rotating blade system moves under certain operating conditions, each bladewill impinge on the tip vortices shed by itself or other blades. This impingement is called a blade-vortex interaction, or BVI. Although the blade an...
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When a rotating blade system moves under certain operating conditions, each bladewill impinge on the tip vortices shed by itself or other blades. This impingement is called a blade-vortex interaction, or BVI. Although the blade and trailing tip vortices interact with many different orientations, one of the two extremes, either parallel or perpendicular interaction, is usually modeled. A parallel interaction has the largest concurrent interaction with the blade, as a result this case is given the most attention. One of the most commonly studied occurrences of blade-vortex interactions is associated with low-speed descending rotorcraft flight. BVI occurs when the tip vortices shed by the blades intersect the plane of the rotor. BVI cause local pressure changes over the blades which are responsible, in part, for the acoustic signature of the rotorcraft. The local pressure changes also cause vibrations which lead to fatigue of both the blades and the mechanical components driving the blades.
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摘要 :
Blade-vortex interaction noises, sometimes referred to as 'blade slap', are avoided by increasing the absolute value of inflow to the rotor system of a rotorcraft. This is accomplished by creating a drag force which causes the ang...
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Blade-vortex interaction noises, sometimes referred to as 'blade slap', are avoided by increasing the absolute value of inflow to the rotor system of a rotorcraft. This is accomplished by creating a drag force which causes the angle of the tip-path plane of the rotor system to become more negative or more positive.
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摘要 :
As a rotor blade moves through the air, it sheds vortices. These vortices shed along the length of the blade over time form the wake. The strongest vortices of the wake are those trailing from the tip of the blade. When a rotating...
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As a rotor blade moves through the air, it sheds vortices. These vortices shed along the length of the blade over time form the wake. The strongest vortices of the wake are those trailing from the tip of the blade. When a rotating blade system moves under certain operating conditions, each blade will impinge on the tip vortices shed by itself or other blades. This impingement is called a blade-vortex interaction, or BVI. Although the blade and trailing tip vortices interact with many different orientations, one of the two extremes, either parallel or perpendicular interaction, is usually modelled. In a perpendicular interaction, the portion of the blade that is actually interacting with the travelling vortex at any given time is very small. A parallel interaction, however, has the largest concurrent interaction with the blade, as a result this case is given the most attention. One of the most commonly studied occurrences of blade-vortex interactions is associated with low-speed descending rotorcraft flight. BVI occur when the tip vortices shed by the blades intersect the plane of the rotor. BVI cause local pressure changes over the blades which are responsible, in part, for the acoustic signature of the rotorcraft. The local pressure changes also cause vibrations which lead to fatigue of both the blades and the mechanical components driving the blades.
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