Instability Mechanisms and Stability Criteria of a Group of Circular Cylinders Subjected to Cross-Flow—Part 2: Numerical Results and Discussions

1983 ◽  
Vol 105 (2) ◽  
pp. 253-260 ◽  
Author(s):  
S. S. Chen
Keyword(s):  
Experimental Data ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Critical Flow ◽  
Stability Criteria ◽  
Flow Part ◽  
Parameter Ranges ◽  
Square Array ◽  
Good Agreement ◽  
Flow Velocities

The fluid-force coefficients for a row of cylinders and a square array are determined from available experimental data and critical flow velocities are calculated as a function of system parameters. Experimental data for critical flow velocities are found to be in good agreement with the analytical results. It is concluded that different stability criteria have to be utilized in different parameter ranges because of different instability mechanisms.

Instability Mechanisms and Stability Criteria of a Group of Circular Cylinders Subjected to Cross-Flow. Part I: Theory

1983 ◽  
Vol 105 (1) ◽  
pp. 51-58 ◽  
Author(s):  
S. S. Chen
Keyword(s):  
Dynamic Instability ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Stability Criteria ◽  
Critical Flow Velocity ◽  
Closed Form Solutions ◽  
Fluid Damping ◽  
Functional Forms ◽  
Flow Part ◽  
The Stability

A mathematical model is presented for a group of circular cylinders subject to cross-flow. It is found that there are two basic dynamic instability mechanisms: instability controlled by fluid damping and instability controlled by fluidelastic force. Approximate closed form solutions of the critical flow velocity for the two mechanisms are obtained based on constrained-mode analyses. The model has identified the key parameters in the stability criteria and their functional forms and resolved the controversy associated with the empirical stability criteria.

Some Issues Concerning Fluid-Elastic Instability of a Group of Circular Cylinders in Cross-Flow

1989 ◽  
Vol 111 (4) ◽  
pp. 507-518 ◽  
Author(s):  
S. S. Chen
Keyword(s):  
Flow Velocity ◽  
State Of The Art ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Critical Flow ◽  
Elastic Instability ◽  
Stability Criteria ◽  
Critical Flow Velocity ◽  
Current State

Since the early 1970s, extensive studies of fluid-elastic instability of circular cylinders in cross-flow have been reported. A significant understanding of the phenomena involved now exists. However, some confusion, misunderstanding, and misinterpretation still remain. The objective of this paper is to discuss, based on the current state of the art, a series of the most asked questions. Emphasis is placed on the determination of the critical flow velocity, nondimensional parameters, stability criteria, and instability mechanisms.

Characteristics of Fluidelastic Instability of Tube Rows in Crossflow

1988 ◽  
Vol 110 (1) ◽  
pp. 1-5
Author(s):  
S. S. Chen ◽  
J. A. Jendrzejczyk
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Diameter Ratio ◽  
Critical Flow ◽  
Jump Phenomenon ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Flow Velocities

An experimental study is reported that investigated the jump phenomenon in critical flow velocities for tube rows with different pitch-to-diameter ratios, and the excited and intrinsic instabilities for a tube row with a pitch-to-diameter ratio of 1.75. The experimental data provide additional insights into the instability phenomena of tube arrays in crossflow.

Experiments on Fluidelastic Instability of Cylinder Clusters in Axial Flow

1982 ◽  
Vol 104 (3) ◽  
pp. 342-347 ◽  
Author(s):  
M. P. Paidoussis ◽  
LI. R. Curling ◽  
J. O. Gagnon
Keyword(s):  
Natural Frequencies ◽  
Axial Flow ◽  
High Flow ◽  
Strain Gauges ◽  
Critical Flow ◽  
Water Tunnel ◽  
Random Vibrations ◽  
General Behavior ◽  
Good Agreement ◽  
Flow Velocities

This paper presents a summary of the general behavior of cylinder clusters in axial flow and especially of the fluidelastic instabilities which occur at high flow velocities. Experiments were conducted in a water tunnel with three- and four-cylinder clusters, and the behavior was monitored either optically or by instrumenting one of the cylinders with strain gauges. With increasing flow, the amplitude of small random vibrations of the cylinders increased; simultaneously, the natural frequencies, as a group, decreased, which is in good agreement with theory. The cylinders eventually lost stability by buckling (divergence), and at higher flow by flutter. Agreement between theoretical and experimental critical flow velocities for these fluidelastic instabilities has been found to be good.

An Assessment of Turbulence Models in Simulating a Synthetic Jet

2013 ◽  
Vol 465-466 ◽  
pp. 603-607
Author(s):  
Greg G. Gomang ◽  
Ann Lee
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Numerical Study ◽  
Cross Flow ◽  
Turbulence Models ◽  
Synthetic Jet ◽  
Shear Stress Transport ◽  
Sst Model ◽  
Realistic Prediction ◽  
Good Agreement

This paper presents a two-dimensional numerical study on the interaction of synthetic jet and the cross flow inside a microchannel. Three different turbulence models namely the standard k-, Shear Stress Transport (SST) and Scale Adaptive Simulation Shear Stress Transport (SAS SST) were tested for their ability to predict the flow structure generated by a synthetic jet. The results are validated against existing experimental data. The SAS SST model was found to give the most realistic prediction of the fluid flow based on the good agreement with experimental data.

Mach Number Scaling of Single-Component, Two-Phase Flow

1993 ◽  
Vol 115 (4) ◽  
pp. 772-777
Author(s):  
D. E. Nikitopoulos
Keyword(s):  
Experimental Data ◽  
Mach Number ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Critical Mass ◽  
Critical Flow ◽  
Phase Flow ◽  
Homogeneous State ◽  
Two Phase ◽  
Good Agreement

A simple two-fluid formulation is used to investigate compressibility effects and Mach number scaling for equilibrium, evaporating two-phase flow. The definition of the local two-phase Mach number emerges from a critical flow analysis. Comparisons of the theoretical critical mass flux with existing experimental data obtained in steam-water flows show very good agreement for moderate and high qualities over a wide critical pressure range. Within this quality range the predicted critical mass flux is quite insensitive to the velocity ratio. The analysis confirms previous observations, based on homogeneous flow models, indicating that in variable area ducts the critical state does not occur at a geometrical throat. Results of existing critical flow experiments in slowly diverging ducts are discussed in the light of this conclusion. A way from the neighborhood of the flash horizon, pressure-drop and kinetic energy changes are shown to scale with similar local Mach functions as those of single-phase compressible flow. Existing experimental data from vertical-upwards and horizontal two-phase flows in pipes indicate that the Mach number calculated on the basis of the local homogeneous state provides the optimum scaling performance. Scaling of the same experimental data using a Mach number based on the local nonhomogeneous state provides results that are in reasonably good agreement with the theoretical scaling guidelines and predictions, but is handicapped by considerable scatter in the scaled experimental variables.

scholarly journals Large Eddy Simulation of Scalar Mixing in Jet in a Cross-Flow

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Asela Uyanwaththa ◽  
Weeratunge. Malalasekera ◽  
Graham Hargrave ◽  
Mark Dubal
Keyword(s):  
Experimental Data ◽  
Velocity Field ◽  
Large Eddy Simulation ◽  
Cross Flow ◽  
Passive Scalar ◽  
Scalar Mixing ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Fuel Mixing ◽  
Good Agreement

Jet in a cross-flow (JICF) is a flow arrangement found in many engineering applications, especially in gas turbine air–fuel mixing. Understanding of scalar mixing in JICF is important for low NOx burner design and operation, and numerical simulation techniques can be used to understand both spatial and temporal variation of air–fuel mixing quality in such applications. In this paper, mixing of the jet stream with the cross-flow is simulated by approximating the jet flow as a passive scalar and using the large eddy simulation (LES) technique to simulate the turbulent velocity field. A posteriori test is conducted to assess three dynamic subgrid scale models in modeling jet and cross-flow interaction with the boundary layer flow field. Simulated mean and Reynolds stress component values for velocity field and concentration fields are compared against experimental data to assess the capability of the LES technique, which showed good agreement between numerical and experimental results. Similarly, time mean and standard deviation values of passive scalar concentration also showed good agreement with experimental data. In addition, LES results are further used to discuss the scalar mixing field in the downstream mixing region.

Applications of Wavelet Neural Network for Prediction of CHF

2011 ◽  
Vol 58-60 ◽  
pp. 1282-1286
Author(s):  
Hui Ming Wei ◽  
Yuan Tian ◽  
Jun Zhong ◽  
Xuan Zhang
Keyword(s):  
Neural Network ◽  
Experimental Data ◽  
Heat Flux ◽  
Linear Problem ◽  
Wavelet Neural Network ◽  
Data Simulation ◽  
Data Points ◽  
Set Up ◽  
Parameter Ranges ◽  
Good Agreement

In this study, a wavelet neural network (WNN) model for predicting critical heat flux (CHF) is set up. The WNN mode combining the properties of the wavelet transform and the advantages of Artificial Neural Networks (ANN) has some advantages of its globe optimal searching, quick convergence speed and solving non-linear problem. The database used in the analysis is from the 1960’s, including 126 data points which cover these parameter ranges: pressure P=100–1,000 kPa, mass flow rate G=40–500 kgm-2s-1, inlet subcooling ΔTsub=0–35◦C and heat flux Q=20–8,000 kWm-2. The WNN prediction results have a good agreement with experimental data. Simulation and analysis results show that the network model can effectively predict CHF.

A Single-Flexible-Cylinder Analysis for the Fluidelastic Instability of an Array of Flexible Cylinders in Cross-Flow

1986 ◽  
Vol 108 (2) ◽  
pp. 193-199 ◽  
Author(s):  
S. J. Price ◽  
M. P. Paidoussis
Keyword(s):  
Experimental Data ◽  
Flow Direction ◽  
Cross Flow ◽  
Critical Flow ◽  
Flexible Cylinder ◽  
Stagnation Region ◽  
Critical Flow Velocity ◽  
Array Pattern ◽  
Damping Parameter ◽  
Fluid Damping

A quasi-static fluidelastic analysis is developed for a single flexible cylinder surrounded by rigid cylinders and subject to cross-flow. Although the analysis is quasi-static, it includes a frequency-dependent term which arises because of flow retardation around the front stagnation region of the cylinder. The combined effect of this flow retardation and of the fluid force field is to produce, for some intercylinder patterns of motion, a negative fluid damping, acting in the sense normal to the flow direction. Using this analysis, the effect of array pattern of the adjacent rigid cylinders is investigated, and it is shown that for some geometries a single flexible cylinder will become unstable while for others it will not. For those array patterns which the theory indicates to be potentially unstable, the variation of critical flow velocity with mass-damping parameter is obtained and compared with available experimental data. In general, the comparison is good, indicating the validity of this analysis.

Development of Numerical Method for Prediction of Maneuvering Performance of Marine Vehicle

2010 ◽  
Vol 44-47 ◽  
pp. 929-934 ◽  
Author(s):  
Lei Yue ◽  
Da Kui Feng ◽  
Zhi Guo Zhang ◽  
Jing Guo Lu ◽  
Shuai Zhang
Keyword(s):  
Experimental Data ◽  
Numerical Method ◽  
Pressure Coefficient ◽  
Cross Flow ◽  
Skin Friction Coefficient ◽  
Circular Motion ◽  
Commercial Code ◽  
Turning Motion ◽  
Marine Vehicle ◽  
Good Agreement

Numerical maneuvering tank (NMT) is developed which could be used for investigating the flow physics involving the interaction of the flow shed from the sail and the cross-flow boundary layer of the hull, interaction between the hull and appendages like rudder and propeller during maneuvering operation. Two numerical codes are used for this study: CADMV (computer aid design of marine vehicle) and FLUENT commercial code. They are validated against each other and compared with experimental measurement results. Pressure coefficient and skin friction coefficient are obtained and compared with experimental data available in the literature. The simulation results show good agreement with the experimental data. NMT was developed based on above numerical method to simulate the circular motion of marine vehicle. The steady, uniform flow fields are obtained and the characteristics of rotation flow show good agreement with actual phenomena. The circular motion simulations of a SUBOFF in NMT is conducted at different angle of drifts of hull. The obtaining of hydrodynamics parameters is very important for accurately predicting the hydrodynamic behavior of a maneuvering marine vehicle in turning motion.

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