Experimental Investigation into the Instability of an Over-Hung Rigid Centrifuge Rotor Partially Filled With Fluid

2002 ◽  
Vol 124 (4) ◽  
pp. 483-491 ◽  
Author(s):  
Zhu Changsheng
Keyword(s):  
Experimental Investigation ◽  
Free Surface ◽  
Upper Bound ◽  
Dynamical Behavior ◽  
Rotor System ◽  
Unstable Region ◽  
Fill Ratio ◽  
Rotor Imbalance ◽  
New Phenomena ◽  
Centrifuge Rotor

The objective of this paper is to experimentally investigate the instability of an over-hung rigid centrifuge rotor partially filled with fluid. Specific emphasis has been placed on the developing process of rotor instability, the dynamical behavior of the rotor system while the instability occurs, and the frequency and direction of rotor whirl within the unstable region of rotational speeds. The effects of fluid-fill ratio on the rotor whirl frequency, the extent of the unstable region of rotational speeds, and the rotor imbalance are also studied. The detailed results clarify some issues and show some new phenomena on the instability of a rotor partially filled with fluid. The phenomena include: sub-synchronous frequency that does not result in instability of the rotor system and disappears in the unstable region at the larger fluid-fill ratios; different whirl frequencies entering the unstable region for slowly increasing and decreasing rotational speed operations; variable whirl frequency within the unstable region; hysteresis at the upper bound of the unstable region; and a break-down of the fluid free-surface.

Instability of an Over-Hung Rigid Centrifuge Rotor Partially Filled With Fluid

2000 ◽  
Author(s):  
Changsheng Zhu ◽  
H. Ulbrich
Keyword(s):  
Free Surface ◽  
Dynamical Behaviour ◽  
Rotor System ◽  
Hysteresis Phenomenon ◽  
Unstable Region ◽  
Fill Ratio ◽  
Rotor Imbalance ◽  
New Phenomena ◽  
First Time ◽  
Centrifuge Rotor

The objective of this paper is to experimentally investigate the instability of an over-hung rigid centrifuge rotor partially filled with fluid. Specific attention is paid to the developing process of rotor instability, the dynamical behaviour of rotor system while the instability occurs, and the whirling frequency and direction of rotor system within the unstable region. The effects of the fluid fill ratio on the whirling frequency, the unstable region and the rotor imbalance are also studied. The results clarify some issues and show many new phenomena about the instability of the rotor partially filled with fluid for the first time. The phenomena include the sub-synchronous frequency that does not result in the instability of rotor system and which disappears in the unstable region at the large fluid fill ratios; different whirling frequencies existing in the unstable region between the slowly increasing and decreasing rotational speed operations, hysteresis phenomenon in the upper side of the unstable region and the breaking-down phenomenon of the fluid free surface.

A note on the instabilities of a horizontal shear flow with a free surface

2000 ◽  
Vol 406 ◽  
pp. 337-346 ◽  
Author(s):  
L. ENGEVIK
Keyword(s):  
Surface Tension ◽  
Free Surface ◽  
Shear Flow ◽  
Velocity Profile ◽  
Froude Number ◽  
The Other ◽  
Algebraic Equations ◽  
Horizontal Shear ◽  
Analytical Treatment ◽  
Unstable Region

The instabilities of a free surface shear flow are considered, with special emphasis on the shear flow with the velocity profile U* = U*0sech2 (by*). This velocity profile, which is found to model very well the shear flow in the wake of a hydrofoil, has been focused on in previous studies, for instance by Dimas & Triantyfallou who made a purely numerical investigation of this problem, and by Longuet-Higgins who simplified the problem by approximating the velocity profile with a piecewise-linear profile to make it amenable to an analytical treatment. However, none has so far recognized that this problem in fact has a very simple solution which can be found analytically; that is, the stability boundaries, i.e. the boundaries between the stable and the unstable regions in the wavenumber (k)–Froude number (F)-plane, are given by simple algebraic equations in k and F. This applies also when surface tension is included. With no surface tension present there exist two distinct regimes of unstable waves for all values of the Froude number F > 0. If 0 < F [Lt ] 1, then one of the regimes is given by 0 < k < (1 − F2/6), the other by F−2 < k < 9F−2, which is a very extended region on the k-axis. When F [Gt ] 1 there is one small unstable region close to k = 0, i.e. 0 < k < 9/(4F2), the other unstable region being (3/2)1/2F−1 < k < 2 + 27/(8F2). When surface tension is included there may be one, two or even three distinct regimes of unstable modes depending on the value of the Froude number. For small F there is only one instability region, for intermediate values of F there are two regimes of unstable modes, and when F is large enough there are three distinct instability regions.

Base-Vented Hydrofoils of Finite Span Under a Free Surface: An Experimental Investigation

1984 ◽  
Vol 28 (02) ◽  
pp. 90-106
Author(s):  
Jacques Verron ◽  
Jean-Marie Michel
Keyword(s):  
Experimental Investigation ◽  
Free Surface ◽  
Flow Rate ◽  
Cavity Length ◽  
Three Dimensional ◽  
Leading Edge ◽  
Pulsation Frequency ◽  
Cavity Pressure ◽  
Air Flow Rate ◽  
Cavity Configuration

Experimental results are given concerning the behavior of the flow around three-dimensional base-vented hydrofoils with wetted upper side. The influence of planform is given particular consideration so that the sections of the foils are simple wedges with rounded noses. Results concern cavity configuration, the relation between the air flow rate and cavity pressure, leading-edge cavitation, cavity length, pulsation frequency, and force coefficients.

scholarly journals EFFECT OF FRICTION ON VIBRATIONAL CHARACTERISTICS OF ROTOR SYSTEM DURING ROTOR-STATOR INTERACTION

2020 ◽  
pp. 22-31
Author(s):  
Anton Kurakin ◽  
Keyword(s):  
Experimental Data ◽  
Experimental Investigation ◽  
Friction Coefficient ◽  
Rotor System ◽  
Aluminum Bronze ◽  
Rotor Systems ◽  
Vibrational Characteristics ◽  
Rotor Stator Interaction ◽  
Intermediate Value ◽  
Impact Motion

Systems operation which include rotating elements in certain cases is associated with occurrence of contact between the rotating parts (rotor) and the stationary parts (stator). There were cases then rotor-stator interaction led to damage or to complete unit destruction. For this reason, rotor-stator interaction is one of the main problem of rotor systems exploitation. The main aim of the work is to gather detail data about effect of friction on vibrational characteristics of rotor system during rotor-stator interaction. In this article the experimental investigation method and experimental investigation of dynamic behavior of rotor during rotor-stator interaction is presented. The analysis of experimental data obtained during interaction between steel rotor and stator made of aluminum, bronze and PTFE is presented. All results with rotor-stator contact and without were compared by using Campbell diagrams, orbits and frequency responses. Analysis of experimental data shows that friction has strong effect on vibrational characteristics of rotor system during rotor-stator interaction. According to friction ratio three kinds of vibrational characteristics of rotor system are distinguished: forward slipping if friction coefficient is small, backward rolling if friction coefficient is big, vibratory impact motion if friction coefficient has intermediate value. Created experimental method and gathered data about rotor dynamics during rotor-stator contact can be used for verification and tuning of mathematical models.

Experimental Investigation of Free Surface Gradients in a 90° Angled Asymmetrical Open Channel Confluence

2018 ◽  
pp. 803-819 ◽  
Author(s):  
Stéphan Creëlle ◽  
Lukas Engelen ◽  
Laurent Schindfessel ◽  
Pedro X. Ramos ◽  
Tom De Mulder
Keyword(s):  
Experimental Investigation ◽  
Free Surface ◽  
Open Channel ◽  
Channel Confluence

An Experimental Investigation on the Response of a Flexible Rotor Mounted in Pressure Dam Bearings

1980 ◽  
Vol 102 (4) ◽  
pp. 842-850 ◽  
Author(s):  
R. D. Flack ◽  
M. E. Leader ◽  
E. J. Gunter
Keyword(s):  
Experimental Investigation ◽  
Rotor System ◽  
Flexible Rotor ◽  
The Stability

The response of a flexible rotor mounted in six bearing sets has been experimentally determined. One set of axial groove bearings and five sets of pressure dam bearings were tested. Conventional synchronous tracking was used in the analysis and other techniques utilizing an FFT analyzer were developed. The stability of the system was seen to strongly depend on the design of the step bearings. The dam bearings were also noted to lock into subsynchronous whip during deceleration after the system went unstable. The response of the system with varying degrees of unbalance is also analyzed and several structural resonances of the rotor system are discussed.

Sign in / Sign up

Export Citation Format

Share Document