Numerical Simulation of Stirrer Oscillations in Consideration of Fluid-Structure-Interaction and Flexible Restraint Systems

2003 ◽  
Author(s):  
Thomas Berger ◽  
Klaus Strohmeier
Keyword(s):  
Rotational Speed ◽  
Fluid Dynamic ◽  
Dynamic Effects ◽  
Resonant Vibrations ◽  
Structural Dynamic ◽  
Structure Interaction ◽  
Critical Rotational Speed ◽  
Method Of Solution ◽  
Fully Coupled ◽  
Good Agreement

Stirrers are subjected to severe damages when the rotational speed n approaches the critical rotational speed nkrit (eigenfrequency). Appearing resonant vibrations result in huge stirrer shaft bending deformations and possible stirrer damages (see Figure 1). The possibilities of an accurate stirrer design (regarding the shaft vibrations) with analytical calculations [Fischer and Strohmeier (2000)] are often very unsatisfactional: The fluid dynamic effects on the structure and the real, often flexible, restraint systems cannot be considered. Both aspects, however, have an important influence, both on the critical rotational speed nkrit, and the oscillation amplitudes of the stirrer. As a method of solution, a fully coupled interaction of flow field and structural dynamic response of the stirrer is implemented in a commercial CFD-Code. The simulated results are compared to experimental data and show good agreement.

Fluid-Structure Interaction of Stirrers in Mixing Vessels: Part II — Fully Coupled Simulation

2002 ◽  
Author(s):  
Thomas Berger ◽  
Bernhard Eckl ◽  
Klaus Strohmeier
Keyword(s):  
Rotational Speed ◽  
Analytical Data ◽  
Coupled Analysis ◽  
Structural Dynamic ◽  
Fluid Medium ◽  
Sliding Mesh ◽  
User Subroutine ◽  
Accurate Design ◽  
Critical Rotational Speed ◽  
Fully Coupled

Mixing Stirrers are subjected to severe damages [Strohmeier (1996), Strohmeier and Ho¨lzl (1998)] when the rotational speed approaches the critical rotational speed nkrit (eigenfrequency). Because of resonant vibrations, the stirrer deflection approaches infinity (no damping case). The possibilities of an accurate design of mixing stirrers with analytical calculations [Fischer and Strohmeier (2000)] are often very unsatisfactional, due to the complex effects of the fluid medium on the structure (impeller), and consequently its critical speed and its vibrational amplitudes cannot be readily defined. To consider transient fluid effects and out-of-balance forces, it is necessary to implement a coupled analysis of flow field and structural dynamic response of the stirrer in the CFD code as a user subroutine. As a new aspect, a rotating grid (sliding mesh) was combined with a deformable grid to simulate the impeller movement. The results are compared to experimental and analytical data and show good agreement.

Numerical Study of the Laminar Flow Past a Rotating Square Cylinder at Low Spinning Rates

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Dipankar Chatterjee ◽  
Satish Kumar Gupta
Keyword(s):  
Rotational Speed ◽  
Stream Flow ◽  
Free Stream ◽  
Stokes Equations ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Low Frequency ◽  
Square Cylinder ◽  
Rotating Circular Cylinder ◽  
Critical Rotational Speed

The fluid dynamic interaction between a uniform free stream flow and the rotation induced flow from a sharp edged body is numerically investigated. A two-dimensional (2D) finite volume based computation is performed in this regard to simulate the laminar fluid flow around a rotating square cylinder in an unconfined medium. Body fitted grid system along with moving boundaries is used to obtain the numerical solution of the incompressible Navier–Stokes equations. The Reynolds number based on the free stream flow is kept in the range 10≤Re≤200 with a dimensionless rotational speed of the cylinder in the range 0≤Ω≤5. At low Re=10, the flow field remains steady irrespective of the rotational speed. For 50≤Re≤200, regular low frequency Kármán vortex shedding (VS) is observed up to a critical rate of rotation (Ωcr). Beyond Ωcr, the global flow shows steady nature, although high frequency oscillations in the aerodynamic coefficients are present. The rotating circular cylinder also shows likewise degeneration of Kármán VS at some critical rotational speed. However, significant differences can be seen at higher rotation. Such fluid dynamic transport around a spinning square in an unconfined free stream flow is reported for the first time.

scholarly journals Computational Liquid Dynamic Simulation Mixing Time from Side Inlet Mixer Tank

2021 ◽  
Vol 5 (1) ◽  
pp. 30-40
Author(s):  
Nadia Mumtazah ◽  
Ainurazis Ramadhana Putraninghadi ◽  
Ni'am Nisbatul
Keyword(s):  
Rotational Speed ◽  
Single Phase ◽  
Rotation Speed ◽  
Fluid Dynamic ◽  
Mixing Time ◽  
Flat Bottom ◽  
Geometric Size ◽  
Cfd Method ◽  
The Impact ◽  
Good Agreement

This study aims to investigate the mixing time of the side-entry mixer tank and the influence of the propeller's rotational speed on mixing time by the Computational Fluid Dynamic (CFD) method. The tank's model is a flat-bottom cylinder tank whose diameter is 40 cm with a 6 cm propeller contains three blades. The tracer, HCL 37%, was injected on the water's surface while the propeller's rotation speed is varied 100 rpm, 200 rpm, 300 rpm, and 400 rpm. The simulation process is examined using CFD FLUENT 17.1, with a turbulence model is k-ɛ RNG. Its conditions are single-phase then proceeded using species transport. Furthermore, the monitoring point's simulation is identical to the experimental data monitoring probe, which is used to inspect the mass fraction at each point. After all, this simulation contains three processes: pre-processing, solving, and post-processing. as a result, the propeller's higher rotational speed makes the mixing time shorter in the CFD method, which has a good agreement with the experimental method. Moreover, this study also examines the impact of the grid's type and the geometric size for the mixing process in the side-entry mixer tank.

Tire Vibrations

1977 ◽  
Vol 5 (4) ◽  
pp. 202-225 ◽  
Author(s):  
G. R. Potts ◽  
C. A. Bell ◽  
L. T. Charek ◽  
T. K. Roy
Keyword(s):  
Natural Frequencies ◽  
Standing Waves ◽  
Resonant Mode ◽  
Mode Shapes ◽  
Resonant Vibrations ◽  
Resonant Frequencies ◽  
Radial Tire ◽  
Analysis Techniques ◽  
Thin Ring ◽  
Good Agreement

Abstract Natural frequencies and vibrating motions are determined in terms of the material and geometric properties of a radial tire modeled as a thin ring on an elastic foundation. Experimental checks of resonant frequencies show good agreement. Forced vibration solutions obtained are shown to consist of a superposition of resonant vibrations, each rotating around the tire at a rate depending on the mode number and the tire rotational speed. Theoretical rolling speeds that are upper bounds at which standing waves occur are determined and checked experimentally. Digital Fourier transform, transfer function, and modal analysis techniques used to determine the resonant mode shapes of a radial tire reveal that antiresonances are the primary transmitters of vibration to the tire axle.

scholarly journals Analysis of Radial Inflow Turbine Losses Operating with Supercritical Carbon Dioxide

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3561
Author(s):  
Antti Uusitalo ◽  
Aki Grönman
Keyword(s):  
Fluid Dynamic ◽  
Dynamic Simulations ◽  
Average Deviation ◽  
Loss Analysis ◽  
Specific Speed ◽  
Loss Models ◽  
Rotor Losses ◽  
Radial Turbines ◽  
Design Power ◽  
Good Agreement

The losses of supercritical CO2 radial turbines with design power scales of about 1 MW were investigated by using computational fluid dynamic simulations. The simulation results were compared with loss predictions from enthalpy loss correlations. The aim of the study was to investigate how the expansion losses are divided between the stator and rotor as well as to compare the loss predictions obtained with the different methods for turbine designs with varying specific speeds. It was observed that a reasonably good agreement between the 1D loss correlations and computational fluid dynamics results can be obtained by using a suitable set of loss correlations. The use of different passage loss models led to high deviations in the predicted rotor losses, especially with turbine designs having the highest or lowest specific speeds. The best agreement in respect to CFD results with the average deviation of less than 10% was found when using the CETI passage loss model. In addition, the other investigated passage loss models provided relatively good agreement for some of the analyzed turbine designs, but the deviations were higher when considering the full specific speed range that was investigated. The stator loss analysis revealed that despite some differences in the predicted losses between the methods, a similar trend in the development of the losses was observed as the turbine specific speed was changed.

The Effect of Track-Seeking Motion on Off-Track Vibrations of the Head Gimbal Assembly in HDDs

2017 ◽  
Author(s):  
Guoqing Zhang ◽  
Hui Li ◽  
Shengnan Shen ◽  
Tan Trinh ◽  
Frank E. Talke ◽  
...  
Keyword(s):  
Fluid Dynamic ◽  
Angular Acceleration ◽  
Sinusoidal Wave ◽  
Interaction Method ◽  
Square Wave ◽  
Structure Interaction ◽  
Head Gimbal Assembly ◽  
Head Positioning ◽  
Mesh Method ◽  
Simulation Results

The effect of track-seeking on off-track residual vibrations of the head-gimbal assembly (HGA) is investigated for air and helium environments using the so-called “fluid dynamic mesh” method and the “fluid-structure interaction” method. Three different angular acceleration profiles (square wave, triangular wave and sinusoidal wave) are investigated as a function of seek time (10 ms and 5 ms). Results show that smoothening of sharp transitions of the seek profile improves the performance of off-track residual vibrations during track-following and shortens the track-following time of the head positioning servo system. In addition, the effect of lateral flow (windage) on off-track residual vibrations during track-following must be considered for a square wave angular acceleration profile. Simulation results show that helium improves the track-following accuracy compared to air due to the lower windage forces acting on the HGA. We observe that the sinusoidal wave angular acceleration performs best among the three angular acceleration profiles investigated. Furthermore, seek time is found to have only a small effect on off-track residual vibrations during track-following.

Fluid dynamic effects of grooves on circular cylinder surface

AIAA Journal ◽  
1991 ◽  
Vol 29 (12) ◽  
pp. 2062-2068 ◽  
Author(s):  
Takeyoshi Kimura ◽  
Michihisa Tsutahara
Keyword(s):  
Circular Cylinder ◽  
Fluid Dynamic ◽  
Cylinder Surface ◽  
Dynamic Effects
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