scholarly journals Experimental investigation of the return flow instability in magnetized spherical Couette flows

2020 ◽  
Vol 32 (12) ◽  
pp. 124119
Author(s):  
J. Ogbonna ◽  
F. Garcia ◽  
T. Gundrum ◽  
M. Seilmayer ◽  
F. Stefani
Keyword(s):  
Experimental Investigation ◽  
Flow Instability ◽  
Return Flow ◽  
Spherical Couette

Experimental investigation of intermittency modes in a spherical Couette flow

2003 ◽  
Vol 48 (6) ◽  
pp. 309-313 ◽  
Author(s):  
S. Ya. Gertsenshtein ◽  
D. Yu. Zhilenko ◽  
O. É. Krivonosova
Keyword(s):  
Experimental Investigation ◽  
Couette Flow ◽  
Spherical Couette Flow ◽  
Spherical Couette

scholarly journals Continuation and stability of rotating waves in the magnetized spherical Couette system: secondary transitions and multistability

2018 ◽  
Vol 474 (2220) ◽  
pp. 20180281 ◽  
Author(s):  
Ferran Garcia ◽  
Frank Stefani
Keyword(s):  
Magnetic Field ◽  
Axial Magnetic Field ◽  
Return Flow ◽  
Rotating Waves ◽  
Periodic Flows ◽  
Moderate Reynolds Number ◽  
Nonlinear Flows ◽  
Spherical Couette ◽  
The Magnetic Field ◽  
Secondary Transitions

Rotating waves (RW) bifurcating from the axisymmetric basic magnetized spherical Couette (MSC) flow are computed by means of Newton–Krylov continuation techniques for periodic orbits. In addition, their stability is analysed in the framework of Floquet theory. The inner sphere rotates while the outer is kept at rest and the fluid is subjected to an axial magnetic field. For a moderate Reynolds number Re  = 10 3 (measuring inner rotation), the effect of increasing the magnetic field strength (measured by the Hartmann number Ha ) is addressed in the range Ha ∈(0, 80) corresponding to the working conditions of the HEDGEHOG experiment at Helmholtz-Zentrum Dresden-Rossendorf. The study reveals several regions of multistability of waves with azimuthal wavenumber m  = 2, 3, 4, and several transitions to quasi-periodic flows, i.e modulated rotating waves. These nonlinear flows can be classified as the three different instabilities of the radial jet, the return flow and the shear layer, as found in the previous studies. These two flows are continuously linked, and part of the same branch, as the magnetic forcing is increased. Midway between the two instabilities, at a certain critical Ha , the non-axisymmetric component of the flow is maximum.

Control of Rotating Stall in the Diffuser of a Low Speed Centrifugal Compressor

2003 ◽  
Author(s):  
Saad A. Ahmed ◽  
Mohamed A. Gadalla
Keyword(s):  
Experimental Investigation ◽  
Centrifugal Compressor ◽  
Flow Instability ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Centrifugal Blower ◽  
Flow Area ◽  
Lower Flow ◽  
Preliminary Results ◽  
Control Delay

An experimental investigation to delay the onset of the rotating stall in the radial diffuser of a centrifugal blower was carried out. The method involved reducing the flow area by 50% at the diffuser exit using throttle rings attached to either diffuser shroud wall, or the diffuser hub wall. Simultaneous attachments of the throttle rings to both the diffuser’s shroud and the hub walls were also made. The following blockage ratios were used: 25% from both walls, 50% from the diffuser shroud and 0% from the diffuser hub and vice versa. The preliminary results suggest that the onset of the flow instability in the diffuser (stall) could be delayed (i.e., lower flow coefficient) when throttle rings were attached to the diffuser walls to reduce its exit flow area. The results also confirmed that the throttle rings could be an effective method to control/delay the stall in the vaneless radial diffuser.

Experimental investigation of draft tube flow instability

2010 ◽  
Vol 12 ◽  
pp. 012044 ◽  
Author(s):  
S Tridon ◽  
S Barre ◽  
G D Ciocan ◽  
P Leroy ◽  
C Ségoufin
Keyword(s):  
Experimental Investigation ◽  
Flow Instability ◽  
Draft Tube ◽  
Tube Flow

scholarly journals Solar Prominence Fine Structure and Dynamics

2013 ◽  
Vol 8 (S300) ◽  
pp. 15-29 ◽  
Author(s):  
Thomas Berger
Keyword(s):  
Fine Structure ◽  
Flow Instability ◽  
Emission Measure ◽  
Return Flow ◽  
Solar Prominence ◽  
Magnetic Flux Ropes ◽  
Structure And Dynamics ◽  
Solar Prominences ◽  
Dem Analysis ◽  
Shear Flow Instability

AbstractWe review recent observational and theoretical results on the fine structure and dynamics of solar prominences, beginning with an overview of prominence classifications, the proposal of possible new “funnel prominence” classification, and a discussion of the recent “solar tornado” findings. We then focus on quiescent prominences to review formation, down-flow dynamics, and the “prominence bubble” phenomena. We show new observations of the prominence bubble Rayleigh-Taylor instability triggered by a Kelvin-Helmholtz shear flow instability occurring along the bubble boundary. Finally we review recent studies on plasma composition of bubbles, emphasizing that differential emission measure (DEM) analysis offers a more quantitative analysis than photometric comparisons. In conclusion, we discuss the relation of prominences to coronal magnetic flux ropes, proposing that prominences can be understood as partially ionized condensations of plasma forming the return flow of a general magneto-thermal convection in the corona.

Numerical Analysis Versus Experimental Investigation of a Distributor-Type Diesel Fuel-Injection System

1994 ◽  
Vol 116 (4) ◽  
pp. 814-830 ◽  
Author(s):  
A. E. Catania ◽  
C. Dongiovanni ◽  
A. Mittica ◽  
M. Badami ◽  
F. Lovisolo
Keyword(s):  
Experimental Investigation ◽  
Numerical Analysis ◽  
Fuel Injection ◽  
Injection Pressure ◽  
Injection System ◽  
Return Flow ◽  
Computer Assisted ◽  
Fuel Injection System ◽  
Flow Restriction ◽  
Nozzle Hole

A production distributor-type fuel-injection system for diesel engines has been extensively investigated via computer-assisted simulation and experimentation. The investigation was mainly aimed at assessing and validating a sophisticated computational model of the system, developed with specific attention given to the pump and to some important aspects concerning the injection pressure simulation, such as the dynamic effects of the injector needle lift, the flow unsteadiness, and compressibility effects on the nozzle-hole discharge coefficient. The pump delivery assembly was provided with a valve of the reflux type. This presented a flat in the collar, forming a return-flow restriction with the seat, and had no retraction piston. A single-spring injector, with a reduced sac volume, was fitted to the system. The numerical analysis of transient flow phenomena linked to the mechanical unit dynamics, including possible cavitation occurrence in the system, was performed using an implicit finite-difference algorithm, previously set up for in-line injection equipment. Particular care was exercised in modeling the distributor pump so as to match the dynamics of the delivery-valve assembly to the pressure wave propagation in the distributor and its outlets. The so-called minor losses were also taken into account and it was ascertained that sudden expansion and contraction losses were significant for the type of pump examined. The experimental investigation was performed on a test bench at practical pump speeds. Pressures were measured in the pumping chamber, at two different pipe locations, and upstream to the needle seat opening passage. This last measurement was taken in order to evaluate the nozzle-hole flow coefficient with the support of the simulation, using experimental values of the needle lift, injection rate, and injected fuel quantity as known variables. The numerical and experimental results were compared and discussed, showing the validity of the model. The injection pressure time history and the influence of the delivery return-flow restriction on the system performance were numerically examined.

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