Potential Amplification Mechanism of Rotor–Stator-Interaction Noise via Spiral-Poiseuille-Flow Instability

AIAA Journal ◽  
2021 ◽  
pp. 1-17
Author(s):  
Takao Suzuki ◽  
Michael L. Shur ◽  
Michael Kh. Strelets ◽  
Andrey K. Travin
Keyword(s):  
Poiseuille Flow ◽  
Flow Instability ◽  
Rotor Stator Interaction ◽  
Amplification Mechanism

On the instability of the flow in a squeeze lubrication film

1990 ◽  
Vol 430 (1879) ◽  
pp. 347-375 ◽  
Keyword(s):  
Reynolds Number ◽  
Poiseuille Flow ◽  
Flow Instability ◽  
Initial Distribution ◽  
Neutral Curve ◽  
Time Dependent ◽  
Order Partial Differential Equation ◽  
Plane Poiseuille Flow ◽  
Disturbance Wave ◽  
Sommerfeld Equation

When two parallel plates move normal to each other with a slow time-dependent speed, the velocity field developed in the intervening film of fluid is approximately that of plane Poiseuille flow, except that the magnitude of the velocity is dependent on time and on the coordinate parallel to the planes. This fact is intrinsic to Reynolds’ lubrication theory, and can be shown to follow from the Navier-Stokes equations when both the modified Reynolds number ( Re M ) and an aspect ratio ( δ ) are small. The modified Reynolds number is the product of δ and an actual Reynolds number ( Re ), which is based on the gap between the planes and on a characteristic velocity. The occurrence of flow instability and of turbulence in the film depend on Re . Typical values of Re , which are known to be required for the linear instability of plane Poiseuille flow, are of order 6000. This condition can be achieved, even if Re M is of order 1, provided that δ is of order 10 -4 . Such parameter values are typical of lubrication problems. The Orr-Sommerfeld equation governing flow instability is derived in this paper by use of the WKBJ technique, δ being the approximate small parameter to represent the small length-scale of the disturbance oscillations compared with the larger scale of the basic laminar flow. However, the coefficients in the Orr-Sommerfeld equation depend on slow space and time variables. Consequently the eigenrelation, derivable from the Orr-Sommerfeld equation and the associated boundary conditions, constitutes a nonlinear first-order partial differential equation for a phase function. This equation is solved by use of Charpit’s method for certain special forms of the time-dependent gap between the planes, followed by detailed numerical calculations. The relation between time-dependence and flow instability is delineated by the calculated results. In detail the nature of the instability can be described as follows. We consider a disturbance wave at or near a particular station, the initial distribution of amplitude being gaussian in the slow coordinate parallel to the planes. In the context of the Orr-Sommerfeld equation and its eigenrelation, the particular station implies an equivalent Reynolds number, while the initial distribution of the disturbance wave implies an equivalent wavenumber. As time increases, the disturbance wave can be considered to move in the instability diagram of equivalent wavenumber against Reynolds number, in the sense that these parameters are time- and space-dependent for the evolution of the disturbance-wave system. For our detailed calculations we use a quadratic approximation to the eigenrelation, an approximation which is quite accurate. If the initial distribution implies a point within the neutral curve, when the plates are squeezed together the equivalent wavenumber falls while the equivalent Reynolds number rises, and amplification takes place until the lower branch of the neutral curve is nearly crossed. If the plates are pulled apart (dilatation) the equivalent wavenumber rises, while the Reynolds number drops, and amplification takes place until the upper branch of the neutral curve has been just crossed. In the case of dilatation the transition from amplification to damping takes place more quickly than for the case of squeezing, in part due to the geometry of the neutral curve.

An Investigation of the IGV/Rotor Interaction in a Low Speed Axial Compressor Using DPIV

2006 ◽  
Author(s):  
Zhiqiang Gong ◽  
Zhiping Li ◽  
Maoyi Li ◽  
Yajun Lu
Keyword(s):  
Flow Field ◽  
Rotor Blade ◽  
Flow Instability ◽  
Dynamic Pressure ◽  
Axial Compressor ◽  
Tip Leakage Flow ◽  
Stall Margin ◽  
Low Speed ◽  
Wide Range ◽  
Rotor Stator Interaction

IGV/rotor interaction phenomenon in axial compressors is important, because different matching states of IGV and rotor can result in significant differences in performance of the compressors. An experimental investigation of IGV/rotor interaction is performed on a one stage low speed axial compressor. The performance of the compressor is measured with the number of IGV varied within a wide range. Different IGV results in very different performance of the compressor, and the performance does not change with the number of IGV monotonously. Flow field around a rotor blade is measured using 2D Digital Particle Image Velocimetry (DPIV) and dynamic pressure probes, without IGV and with the IGV which brings the largest stall margin to the compressor. Comparison of flow fields reveals that the IGV wakes change the flow field around the rotor blade significantly. The wake of the rotor blade is weakened and its structure is changed. The rotor exit total pressure is elevated throughout the entire span. The tip leakage flow is suppressed, so relevant blockage is reduced and consequently the stable operating range of the compressor is extended. The relatively high turbulence intensity and periodic changes in flow velocity and direction brought by IGV wakes to the rotor may account for some of the observed changes in the flow field structure and the compressor performance. The flow instability and receptivity theory must be included to explain all the experimental results, and to utilize the rotor/stator interaction phenomena during the compressors design process.

Effect of vortex line distribution in superfluid plane Poiseuille flow instability

2013 ◽  
Vol 720 ◽  
Author(s):  
R. Sooraj ◽  
A. Sameen
Keyword(s):  
Poiseuille Flow ◽  
Vortex Line ◽  
Flow Instability ◽  
Mutual Friction ◽  
Plane Poiseuille Flow ◽  
Normal Fluid ◽  
Friction Mode ◽  
Classical Plane ◽  
Mode Stability ◽  
Classical Mode

AbstractThe hydrodynamic stability of plane Poiseuille flow of superfluid is studied using modal and non-modal analysis. Two modes of instability are predicted, in normal mode stability analysis of the normal fluid, one caused by viscosity similar to the classical mode and another due to mutual friction between superfluid and normal fluid. The mutual friction mode occurs at high wavenumbers, which are stable wavenumbers in classical plane Poiseuille flow. A high superfluid vortex line density alone is not enough to induce instability in normal fluid; a localization of vortex lines is shown to play a major role. The extent of vortex line concentration required to cause instability depends on the density itself. Non-modal instability analysis shows that oblique waves are stronger than streamwise waves, unlike the scenario in classical plane Poiseuille flow.

scholarly journals Effects of the Rates on the Performance and Pressure Pulsations of a High-Speed Pump with Straight Blade

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Hao Jia ◽  
Xianghui Su ◽  
Wei Jin
Keyword(s):  
Pressure Fluctuation ◽  
High Speed ◽  
Transient Flow ◽  
Flow Instability ◽  
Harmonic Wave ◽  
Dynamic Performance ◽  
Mechanical Vibration ◽  
Straight Blade ◽  
Blade Passing Frequency ◽  
Rotor Stator Interaction

Along with the crucial requirement for efficiency improvement in the cutting-edge petrochemical technology, the evaluation of the dynamic performance characteristics of high-speed pump is becoming increasingly important. It has become a main topic in the research of high-speed pump to minimize the pressure pulsation induced by the fluid in the pump body, so as to reduce the mechanical vibration. Although the research on the transient flow characteristic and pressure fluctuation of a high-speed pump with straight blades is of great significance, it has been seldom explored. In this work, the flow instability of a 16 straight-blade high-speed centrifugal pump is studied numerically at a rotational speed of 8500 rpm and flow rate of 3 m3/h. Results show that with the influence of rotor-stator interaction, time-domain pressure signals at the tongue show double peak characteristic, whereas a single peak characteristic exists at the diffuser wall. The pressure fluctuation near the tongue is reduced to approximately half of that at the volute wall by the water ring effect accompanied with the high-pressure factor. At the tongue region, the amplitude of the blade passing frequency is reduced by the unsteady flow, whereas the harmonic wave was increased at 2–4 times of the blade passing frequency.

scholarly journals Dynamic Instability Analysis of a Double-Blade Centrifugal Pump

2021 ◽  
Vol 11 (17) ◽  
pp. 8180
Author(s):  
Denghao Wu ◽  
Songbao Yao ◽  
Renyong Lin ◽  
Yun Ren ◽  
Peijian Zhou ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Dynamic Instability ◽  
Flow Instability ◽  
Design Feature ◽  
Internal Flow ◽  
Low Flow ◽  
Pressure Pulsations ◽  
Frequency Spectra ◽  
Rotor Stator Interaction ◽  
The Time Domain

The flow instability of a double-blade centrifugal pump is more serious due to its special design feature with two blades and large flow passages. The dynamic instabilities and pressure pulsations can affect the pump performance and operating lifetime. In the present study, a numerical investigation of unsteady flow and time variation of pressure within a complete double-blade centrifugal pump was carried out. The time domain and frequency domain of pressure pulsations were extracted at 16 monitoring locations covering the important regions to analyze the internal flow instabilities of the pump model. The frequency spectra of pressure pulsations were decomposed into Strouhal number dependent functions. This led to the conclusion that the blade passing frequency (BPF) related vibrations are exclusively flow-induced. Large vortices were observed in the flow passages of the pump at low flow rate. It is noted that high vorticity magnitude occurred in the vicinities of the blade trailing edge and tongue of the volute, due to the rotor-stator interaction between impeller and volute.

Analysis of the Rotor-Stator Interaction in a Radial Flow Pump

2009 ◽  
pp. 141-151 ◽  
Author(s):  
G. Cavazzini ◽  
G. Pavesi ◽  
G. Ardizzon ◽  
P. Dupont ◽  
S. Coudert ◽  
...  
Keyword(s):  
Radial Flow ◽  
Rotor Stator Interaction ◽  
Radial Flow Pump ◽  
Flow Pump
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