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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Medical & biological engineering & computing 17 (1979), S. 192-198 
    ISSN: 1741-0444
    Keywords: Collapsible tube ; Elastic jump ; Elastic tube ; Wavespeed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The behaviour of the flow regime downstream of the choke point in a flow-limited water filled penrose tube was examined. The transmural pressure along the length of the tube was measured with a moveable side-tap catheter and tube area and stiffness were derived from the tube's static pressure/area curve. Stable supercritical flow, in which the local fluid velocity is greater than the local speed of wave propagation, was demonstrated to extend downstream from the choke point. Speed ratios (fluid velocity divided by tube wavespeed) as large as ten were measured in tube segments in which the area changed so gradually with length as to rule out significant longitudinal tension effects on the tube pressure/area curve. The predicted transition from supercritical to subcritical velocity, or elastic jump, was also studied. Sidewall friction along the jump and longitudinal tension effects due to longitudinal wall curvature were found to be significant factors governing the variation of pressure within the jump. Taking friction into account, the flow momentum equation was found to describe the overall size of the elastic jump adequately if its upstream and downstream limits were taken at points where wall curvature effects were negligible.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2016-06-07
    Description: A series of experiments was performed on a 1.8-m-diam model rotor in hover for the principal purpose of investigating the lead-lag stability of isolated bearingless rotors. Incidental to those tests, at least three types of pitch-flap flutter were encountered. Type 1 flutter occurred approximately at the second flap-mode frequency on both two-and three-bladed rotors for both small and large pitch angles and appeared to be a classic pitch-flap flutter. Type 2 flutter showed mostly torsional motion and was seen on both two- and three-bladed rotors. Type 3 flutter was a regressing flap flutter that occurred for only the three-bladed rotor configurations and appears to be a wake excited flutter. Although flutter occurred on a number of different configurations, no rotor parameters were identified that were clearly stabilizing or destabilizing.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA. Ames Research Center Rotorcraft Dynamics 1984; p 69-88
    Format: application/pdf
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