Measurement of the Propagation of Long-Wavelength Disturbances Through Turbulent Flow in Tubes

1976 ◽  
Vol 98 (1) ◽  
pp. 70-78 ◽  
Author(s):  
D. L. Margolis ◽  
F. T. Brown
Keyword(s):  
Small Amplitude ◽  
Eddy Viscosity ◽  
Flow Model ◽  
Transition Band ◽  
Low Frequencies ◽  
Long Wavelength ◽  
Phase Velocities ◽  
Eddy Viscosity Model ◽  
Turbulence Production ◽  
Factor Data

Phase velocities and attenuation factors for the propagation of small amplitude long wavelength sinusoidal disturbances, measured in a tube with turbulent liquid flow, are reported. Three frequency bands are delineated. A quasi-steady-flow model, based primarily on friction-factor data, is corroborated at low frequencies. An eddy-viscosity model, in which the energy of turbulence fails to respond in quasi-steady fashion to the sinusoidal disturbances, is corroborated at higher frequencies. In a predicted transition band unexpected and dramatic peaks in attenuation and phase velocity were found. A discussion suggests that the phenomenon may be related to deterministic aspects of turbulence production.

scholarly journals On the extension of the eddy viscosity model to compressible flows

2014 ◽  
Vol 26 (4) ◽  
pp. 041702 ◽  
Author(s):  
M. Germano ◽  
A. Abbà ◽  
R. Arina ◽  
L. Bonaventura
Keyword(s):  
Compressible Flows ◽  
Eddy Viscosity ◽  
Viscosity Model ◽  
Eddy Viscosity Model

An Assessment of Three-Dimensional Turbulent Boundary Layer Prediction Methods

1973 ◽  
Vol 95 (3) ◽  
pp. 415-421 ◽  
Author(s):  
A. J. Wheeler ◽  
J. P. Johnston
Keyword(s):  
Boundary Layer ◽  
Eddy Viscosity ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Eddy Viscosity Model ◽  
Separating Flow ◽  
Dimensional Boundary ◽  
Stress Models

Predictions have been made for a variety of experimental three-dimensional boundary layer flows with a single finite difference method which was used with three different turbulent stress models: (i) an eddy viscosity model, (ii) the “Nash” model, and (iii) the “Bradshaw” model. For many purposes, even the simplest stress model (eddy viscosity) was adequate to predict the mean velocity field. On the other hand, the profile of shear stress direction was not correctly predicted in one case by any model tested. The high sensitivity of the predicted results to free stream pressure gradient in separating flow cases is demonstrated.

Simulation of Multi-Stage Compressor at Off-Design Conditions

2017 ◽  
Author(s):  
Feng Wang ◽  
Mauro Carnevale ◽  
Luca di Mare ◽  
Simon Gallimore
Keyword(s):  
Mass Flow ◽  
High Speed ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Viscosity Model ◽  
Eddy Viscosity Model ◽  
Multi Stage ◽  
Pressure Profiles ◽  
Non Linear ◽  
The Right

Computational Fluid Dynamics (CFD) has been widely used for compressor design, yet the prediction of performance and stage matching for multi-stage, high-speed machines remain challenging. This paper presents the authors’ effort to improve the reliability of CFD in multistage compressor simulations. The endwall features (e.g. blade fillet and shape of the platform edge) are meshed with minimal approximations. Turbulence models with linear and non-linear eddy viscosity models are assessed. The non-linear eddy viscosity model predicts a higher production of turbulent kinetic energy in the passages, especially close to the endwall region. This results in a more accurate prediction of the choked mass flow and the shape of total pressure profiles close to the hub. The non-linear viscosity model generally shows an improvement on its linear counterparts based on the comparisons with the rig data. For geometrical details, truncated fillet leads to thicker boundary layer on the fillet and reduced mass flow and efficiency. Shroud cavities are found to be essential to predict the right blockage and the flow details close to the hub. At the part speed the computations without the shroud cavities fail to predict the major flow features in the passage and this leads to inaccurate predictions of massflow and shapes of the compressor characteristic. The paper demonstrates that an accurate representation of the endwall geometry and an effective turbulence model, together with a good quality and sufficiently refined grid result in a credible prediction of compressor matching and performance with steady state mixing planes.

Improved compressor corner separation prediction using the quadratic constitutive relation

2017 ◽  
Vol 231 (7) ◽  
pp. 618-630 ◽  
Author(s):  
Xinrong Su ◽  
Xin Yuan
Keyword(s):  
Constitutive Relation ◽  
Eddy Viscosity ◽  
Pressure Coefficient ◽  
Momentum Equation ◽  
Viscosity Model ◽  
Corner Separation ◽  
Pressure Loss Coefficient ◽  
Eddy Viscosity Model ◽  
Relation Model ◽  
Separation Size

This work presents the implementation and study of the quadratic constitutive relation nonlinear eddy-viscosity model with representative compressor application, for which the corner separation has been poorly predicted with the widely used linear Boussinesq eddy-viscosity model. With the introduction of the Reynolds stress anisotropy, the secondary flow of the second kind and its effect on the corner flow can be well captured and this results in greatly improved prediction of pressure coefficient, total pressure loss coefficient and the corner separation size. Without the quadratic constitutive relation model, the separation size and loss are generally over-estimated. The mechanism of the improvement is studied using both the vortex dynamics and the momentum equation. It is proved that quadratic constitutive relation model consumes low CPU time and provides much improved compressor corner separation prediction without worsening the convergence property.

A Three-Equation Eddy-Viscosity Model for Reynolds-Averaged Navier–Stokes Simulations of Transitional Flow

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
D. Keith Walters ◽  
Davor Cokljat
Keyword(s):  
Boundary Layer ◽  
Turbulent Flows ◽  
Eddy Viscosity ◽  
Flow Behavior ◽  
Applied Pressure ◽  
Plate Boundary ◽  
Low Frequency ◽  
Transitional Flow ◽  
Test Cases ◽  
Eddy Viscosity Model

An eddy-viscosity turbulence model employing three additional transport equations is presented and applied to a number of transitional flow test cases. The model is based on the k-ω framework and represents a substantial refinement to a transition-sensitive model that has been previously documented in the open literature. The third transport equation is included to predict the magnitude of low-frequency velocity fluctuations in the pretransitional boundary layer that have been identified as the precursors to transition. The closure of model terms is based on a phenomenological (i.e., physics-based) rather than a purely empirical approach and the rationale for the forms of these terms is discussed. The model has been implemented into a commercial computational fluid dynamics code and applied to a number of relevant test cases, including flat plate boundary layers with and without applied pressure gradients, as well as a variety of airfoil test cases with different geometries, Reynolds numbers, freestream turbulence conditions, and angles of attack. The test cases demonstrate the ability of the model to successfully reproduce transitional flow behavior with a reasonable degree of accuracy, particularly in comparison with commonly used models that exhibit no capability of predicting laminar-to-turbulent boundary layer development. While it is impossible to resolve all of the complex features of transitional and turbulent flows with a relatively simple Reynolds-averaged modeling approach, the results shown here demonstrate that the new model can provide a useful and practical tool for engineers addressing the simulation and prediction of transitional flow behavior in fluid systems.

scholarly journals THE HYDRODYNAMICAL LIMIT OF QUANTUM HALL SYSTEM

2001 ◽  
Vol 15 (19n20) ◽  
pp. 2771-2781 ◽  
Author(s):  
D. SREEDHAR BABU ◽  
R. SHANKAR ◽  
M. SIVAKUMAR
Keyword(s):  
Landau Level ◽  
Small Amplitude ◽  
Quantum Hall ◽  
Collective Excitations ◽  
Current Form ◽  
Long Wavelength ◽  
Lowest Landau Level ◽  
Hydrodynamical Limit ◽  
Quantum Hall System ◽  
A Current

We study the current algebra of FQHE systems in the hydrodynamical limit of small amplitude, long-wavelength fluctuations. We show that the algebra simplifies considerably in this limit. The Hamiltonian is expressed in a current–current form and the operators creating inter-Landau level and lowest Landau level collective excitations are identified.

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