Transient Dynamic Analysis of Rotors Using SMAC Techniques: Part 2, Numerical Study

1992 ◽  
Vol 114 (4) ◽  
pp. 482-488 ◽  
Author(s):  
S. Ratan ◽  
J. Rodriguez
Keyword(s):  
Numerical Study ◽  
Time Domain Analysis ◽  
Superposition Method ◽  
Step Size ◽  
Time Step ◽  
Transient Dynamic Analysis ◽  
Transient Time ◽  
Rotor Systems ◽  
Time Step Size ◽  
And Performance

A new method for performing transient time-domain analysis of rotor systems using a Successive Merging and Condensation (SMAC) technique was introduced in Part 1. This approach can be applied to rotor analysis problems formulated with the finite element method. A numerical study, including examples, comparison of methods, and performance evaluation, is presented here. Validation and applicability of the SMAC method are illustrated with three examples: conservative, nonconservative, and nonlinear. The SMAC algorithm is then compared to the following methods: Transfer Matrix Method (TMM), Modal Superposition Method, and Runge-Kutta Method, and is demonstrated to be computationally more efficient in terms of CPU time and storage space. The issues of stability and time-step size are also studied.

Numerical Study on the Effect of a Volute on Surge Phenomena in a Centrifugal Compressor

2016 ◽  
Author(s):  
S. H. Jeon ◽  
D. H. Hwang ◽  
J. H. Park ◽  
C. H. Kim ◽  
J. H. Baek ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Stokes Equations ◽  
Flow Instability ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Unstable Flow ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Blade Passing Frequency

Numerical investigation of the effect of the volute on stall flow phenomenon is presented by solving three-dimensional Reynolds-averaged compressible Navier-Stokes equations. Two different configurations of a centrifugal compressor were used to compare their performance: One is an original centrifugal compressor which is composed of impeller, splitter, vaned diffuser and a volute and the other is the one without a volute. Steady calculations were performed to predict aerodynamic performance in terms of the pressure ratio, efficiency and mass flow rate. The results show that the operating range of the compressor with a volute is narrower than that of the compressor without a volute. This can be interpreted that flow instability is strongly influenced by the tongue of a volute which is highly asymmetric. Unsteady calculations were also performed with a time-step size of 38μs corresponding to a pitch angle of 5 degrees at the given rotational speed. The flow characteristics for two configurations are analyzed and compared at various instantaneous times showing unsteady dynamic features. Based on the unsteady flow simulation, fast Fourier transform at several discrete points in semi-vaneless space was performed at peak efficiency and near surge point in order to illustrate the unstable flow physics in both configurations. It is found that the blade passing frequency is dominant, indicating that diffuser passages have a periodicity of 40 degrees due to the rotational blades. Besides blade passing frequency, there were several noticeable frequencies which affect the instability of the whole system. Those frequencies in both configurations are compared and analyzed in various aspects.

scholarly journals Numerical Study on Catalytic Hydrodeoxygenation of Pyrolytic Bio-Oil Model Compound, Guaiacol, in Fluidized Bed Reactor

2021 ◽  
Author(s):  
Ogene Fortunate ◽  
Nanda Kishore
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Model Compound ◽  
Numerical Study ◽  
Thermochemical Conversion ◽  
Fluidised Bed ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Bio Oil

Abstract The bio-oil obtained by thermochemical conversion of lignocellulosic biomass consist of large fractions of oxygenated compounds which deteriorate its quality leading to low calorific value, high viscosity, high density, high moisture content, etc. Therefore, the bio-oil should be deoxygenated using hydrogen in the presence of appropriate catalyst to improve its properties. Adequate literature on pyrolysis of biomass within the framework of computational fluid dynamics is available but only a couple of papers available on hydrodeoxygenation of bio-oil obtained by pyrolysis. Thus, in this study, guaiacol has been selected as a representative model compound of phenolic fraction of bio-oil for upgrading it by catalytic hydrodeoxygenation. The reaction process has been implemented in a fluidised bed reactor in the presence of palladium catalyst, Pd/Al 2 O 3 using computational fluid dynamics (CFD) based solver, ANSYS Fluent 14.5. The range of conditions considered herein are: weight-hourly space velocity (WHSV) = 1, 3 and 5 h -1 ; superficial H 2 -gas velocity, u = 0.075, 0.15 and 0.25 m/s; catalyst load = 0.06 kg and temperature, T = 548 K, 573 K, and 598 K. The solver has been thoroughly validated in terms of grid dependence study, time step size dependence study validating hydrodynamics and HDO results wherever possible with existing literature results. The HDO of guaiacol produces phenol as the most abundant compound along with significant amount of cyclopentanone and methanol. The formation of cyclopentanone from HDO of guaiacol is favourable at high temperature whereas low temperature conditions favour formation of methanol and phenol.

scholarly journals Numerical Study of a Francis Turbine over Wide Operating Range: Some Practical Aspects of Verification

2020 ◽  
Vol 12 (10) ◽  
pp. 4301
Author(s):  
Chirag Trivedi ◽  
Igor Iliev ◽  
Ole Gunnar Dahlhaug
Keyword(s):  
Numerical Model ◽  
Transport Model ◽  
Numerical Study ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Step Size ◽  
Time Step ◽  
Angular Rotation ◽  
Time Step Size ◽  
Automatic Optimization

Hydropower plays an essential role in maintaining energy flexibility. Modern designs focus on sustainability and robustness using different numerical tools. Automatic optimization of the turbines is widely used, including low, mini and micro head turbines. The numerical techniques are not always foolproof in the absence of experimental data, and hence accurate verification is a key component of automatic optimization processes. This work aims to investigate the newly designed Francis runner for flexible operation. Unsteady simulations at 80 operating points of the turbine were conducted. The numerical model consisted of 16 million nodes of hexahedral mesh. A SAS-SST (scale adaptive simulation-shear stress transport) model was enabled for resolving/modeling the turbulent flow. The selected time-step size was equivalent to one-degree angular rotation of the runner. Global parameters, such as efficiency, torque, head and flow rate were considered for proper verification and validation. (1) A complete hill diagram of the turbine was prepared and verified with the reference case. (2) The relative error in hydraulic efficiency was computed and the over trend was studied. This allowed us to investigate the consistency of the numerical model under extreme operating conditions, far away from the best efficiency point. (3) Unsteady fluctuations of runner output torque were studied to identify unstable regions and magnitude of torque oscillations.

A Numerical Study of BWR Steam Separator

2002 ◽  
Author(s):  
Haruo Terasaka ◽  
Sensuke Shimizu
Keyword(s):  
Transient Flow ◽  
Numerical Study ◽  
Fluid Model ◽  
Flow Analysis ◽  
Phase Flow ◽  
Step Size ◽  
Time Step ◽  
Two Phase ◽  
Time Step Size ◽  
Steam Separator

An advanced numerical method based on two-fluid model of two-phase flow has been developed to simulate the swirling gas-liquid flow and the phase separation process in a Boiling Water Reactor separator. The goal is to correctly predict the performance of operating steam separator as well as new designs. The solution method present here is an extension of SIMPLEST scheme, a fully implicit scheme for single-phase flow analysis. It is robust and unconditionally stable, therefore enable us to use very large time step size. This feature is suitable for steady and/or slow transient flow analyses. Furthermore, it enhances numerical stability during rapid transient calculations. By employing this method, separator hydrodynamics around swirler were calculated.

scholarly journals Analysis of a Decoupled Time-Stepping Scheme for Evolutionary Micropolar Fluid Flows

2016 ◽  
Vol 2016 ◽  
pp. 1-13 ◽  
Author(s):  
S. S. Ravindran
Keyword(s):  
Micropolar Fluid ◽  
Stokes Equations ◽  
Fluid Model ◽  
Navier Stokes ◽  
Optimal Order ◽  
Step Size ◽  
Time Step ◽  
Order Error ◽  
Time Step Size ◽  
Time Stepping

Micropolar fluid model consists of Navier-Stokes equations and microrotational velocity equations describing the dynamics of flows in which microstructure of fluid is important. In this paper, we propose and analyze a decoupled time-stepping algorithm for the evolutionary micropolar flow. The proposed method requires solving only one uncoupled Navier-Stokes and one microrotation subphysics problem per time step. We derive optimal order error estimates in suitable norms without assuming any stability condition or time step size restriction.

On the Influence of Inflow Model Selection for Time-Domain Tiltrotor Aeroelastic Analysis

2021 ◽  
Author(s):  
Ethan Corle ◽  
Matthew Floros ◽  
Sven Schmitz
Keyword(s):  
Experimental Data ◽  
Particle Method ◽  
Comprehensive Analysis ◽  
Solution Stability ◽  
Step Size ◽  
Time Step ◽  
Time Step Size ◽  
Vortex Particle Method ◽  
Whirl Flutter ◽  
Vortex Particle

The methods of using the viscous vortex particle method, dynamic inflow, and uniform inflow to conduct whirl-flutter stability analysis are evaluated on a four-bladed, soft-inplane tiltrotor model using the Rotorcraft Comprehensive Analysis System. For the first time, coupled transient simulations between comprehensive analysis and a vortex particle method inflow model are used to predict whirl-flutter stability. Resolution studies are performed for both spatial and temporal resolution in the transient solution. Stability in transient analysis is noted to be influenced by both. As the particle resolution is refined, a reduction in simulation time-step size must also be performed. An azimuthal time step size of 0.3 deg is used to consider a range of particle resolutions to understand the influence on whirl-flutter stability predictions. Comparisons are made between uniform inflow, dynamic inflow, and the vortex particle method with respect to prediction capabilities when compared to wing beam-bending frequency and damping experimental data. Challenges in assessing the most accurate inflow model are noted due to uncertainty in experimental data; however, a consistent trend of increasing damping with additional levels of fidelity in the inflow model is observed. Excellent correlation is observed between the dynamic inflow predictions and the vortex particle method predictions in which the wing is not part of the inflow model, indicating that the dynamic inflow model is adequate for capturing damping due to the induced velocity on the rotor disk. Additional damping is noted in the full vortex particle method model, with the wing included, which is attributed to either an interactional aerodynamic effect between the rotor and the wing or a more accurate representation of the unsteady loading on the wing due to induced velocities.

A Strategy to Accelerate the Numerical Integration in the Dynamic Simulation of Multibody Systems

1997 ◽  
Author(s):  
Jesús Cardenal ◽  
Javier Cuadrado ◽  
Eduardo Bayo
Keyword(s):  
Multibody Systems ◽  
Equations Of Motion ◽  
Stiff Systems ◽  
Step Size ◽  
Step Method ◽  
Integral Of Motion ◽  
Time Step ◽  
Time Step Size ◽  
Variable Time ◽  
Numerical Integrator

Abstract This paper presents a multi-index variable time step method for the integration of the equations of motion of constrained multibody systems in descriptor form. The basis of the method is the augmented Lagrangian formulation with projections in index-3 and index-1. The method takes advantage of the better performance of the index-3 formulation for large time steps and of the stability of the index-1 for low time steps, and automatically switches from one method to the other depending on the required accuracy and values of the time step. The variable time stepping is accomplished through the use of an integral of motion, which in the case of conservative systems becomes the total energy. The error introduced by the numerical integrator in the integral of motion during consecutive time steps provides a good measure of the local integration error, and permits a simple and reliable strategy for varying the time step. Overall, the method is efficient and powerful; it is suitable for stiff and non-stiff systems, robust for all time step sizes, and it works for singular configurations, redundant constraints and topology changes. Also, the constraints in positions, velocities and accelerations are satisfied during the simulation process. The method is robust in the sense that becomes more accurate as the time step size decreases.

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