Unsteady Potential Flow Theory and Numerical Analysis of Forces on Cylinders Induced by Nearby Oscillating Disturbances

2009 ◽  
Author(s):  
Daniel T. Valentine ◽  
Farshad Madhi
Keyword(s):  
Numerical Model ◽  
Unsteady Flow ◽  
Potential Flow ◽  
Complete Solution ◽  
Boundary Integral ◽  
Circular Cylinders ◽  
Two Dimensional ◽  
Method Of Images ◽  
Surface Distribution ◽  
Flow Problems

The complete solution of several two-dimensional potential flow problems are reported that deal with the unsteady flow around circular cylinders. Three of the flows considered are induced by an oscillating disturbance near the cylinder. The three elemental disturbances examined are (1) a pulsating source, (2) a pulsating doublet and (3) a pulsating vortex. The formulas for the force acting on the cylinder due to each of the elemental disturbances were derived by applying the method of images and checked by deriving the equivalent surface distribution of sources to model the cylinder starting with Green’s second identity. The theory helped direct the development of a boundary-integral numerical model described and applied in this paper to solve the unsteady flow around a circular cylinder due to an arbitrarily specified oscillatory disturbance near the cylinder. The numerical method is validated by comparing predictions of the force with the exact solutions.

Potential Flow Theory and Numerical Analysis of Forces on Cylinders Induced by Oscillating Disturbances

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Daniel T. Valentine ◽  
Farshad Madhi
Keyword(s):  
Unsteady Flow ◽  
Vortex Shedding ◽  
Potential Flow ◽  
Model Problem ◽  
Complete Solution ◽  
Boundary Integral ◽  
Circular Cylinders ◽  
Method Of Images ◽  
Surface Distribution ◽  
Flow Problems

The complete solution of several two-dimensional potential flow problems are reported that deal with the unsteady flow around circular cylinders. Three of the flows considered are induced by an oscillating disturbance near the cylinder. The three elemental disturbances examined are (1) a pulsating source, (2) a pulsating doublet, and (3) a pulsating vortex. The formulas for the force acting on the cylinder due to each of the elemental disturbances were derived by applying the method of images. These results were checked by deriving the equivalent surface distribution of sources to model the cylinder by applying Green’s second identity. The theory helped direct the development of a boundary-integral numerical model described and applied in this paper to solve the unsteady flow around a circular cylinder due to an arbitrarily specified oscillatory disturbance near the cylinder. The numerical method is validated by comparing predictions of the force with the exact solutions. We applied the theory to examine a model problem related to the vortex-shedding force that causes vortex-induced vibration.

Numerical Model of Three-Dimensional Motion of Plate-Type Wind-Borne Debris Based on Quaternions and its Improvement in Unsteady Flow

2013 ◽  
Vol 405-408 ◽  
pp. 2399-2408 ◽  
Author(s):  
An Min Fu ◽  
Peng Huang ◽  
Ming Gu
Keyword(s):  
Numerical Model ◽  
Unsteady Flow ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Moment Coefficient ◽  
Flight Mode ◽  
Gimbal Lock ◽  
Improved Model ◽  
Plate Type ◽  
Good Agreement

A numerical model of three-dimensional motion of plate-type wind-borne debris in uniform wind field based on quaternions is proposed in this paper. This model can simulate the complex 3D spinning flight robustly and efficiently with rotational quaternions, which are also free from the gimbal lock that is associated with Euler rotational matrix. The predictions from the model were then compared with the results of another quasi-steady model, and good agreement is found. For the unsteady flow involved in autorotational flight mode, the present model was improved by revising the damping moment in order to simulate the two-dimensional motion of plates with higher accuracy. Calibration of the damping moment coefficient was performed through a direct comparison of the predicted non-dimensional angular velocity with the results of CFD-RBD model. The predictions of the improved model agree reasonably well with the CFD-RBD results, which verifies the accuracy of the improved model in predicting the two-dimensional trajectories of plates.

Potential Flow Past a Group of Circular Cylinders

1971 ◽  
Vol 93 (4) ◽  
pp. 636-642 ◽  
Author(s):  
C. Dalton ◽  
R. A. Helfinstine
Keyword(s):  
Potential Flow ◽  
Lift Coefficient ◽  
Controlling Factors ◽  
Circular Cylinders ◽  
Method Of Images ◽  
Single Cylinder ◽  
Flow Past ◽  
Inertial Coefficient

The problem of an accelerating potential flow past a group of stationary circular cylinders is considered using the method of images. The problem is formulated so that the number and location of the cylinders is arbitrary so long as there is no overlap between adjacent cylinders. Inertial and lift coefficients are determined for several different cylinder arrangements. The inertial coefficient for a cylinder can vary in either direction from its single-cylinder value of 2.0. The controlling factors on this variation are the relative geometric position of the cylinder within the group and its distance from its neighbors. These same factors determine, as is expected, the lift coefficient values. In two example configurations, there is even a drag-type force generated on an individual cylinder in the potential flow.

Flows of thin streams with free boundaries

1973 ◽  
Vol 59 (3) ◽  
pp. 417-432 ◽  
Author(s):  
Joseph B. Keller ◽  
James Geer
Keyword(s):  
Channel Flow ◽  
Potential Flow ◽  
Slenderness Ratio ◽  
Asymptotic Series ◽  
Two Dimensional ◽  
Free Boundaries ◽  
Complex Flow ◽  
Flow Problems ◽  
Different Types ◽  
Wall Flow

A method is developed for determining any thin steady two-dimensional potential flow with free and/or rigid boundaries in the presence of gravity. The flow is divided into a number of parts and in each part the flow and its free boundaries are represented as asymptotic series in powers of the slenderness ratio of the stream. There are three basic flows, having two, one and no free boundaries and called jet flow, wall flow and channel flow, respectively. First the three expansions for these flows are found, extending results of Keller & Weitz (1952). They are called outer expansions to distinguish them from the inner expansions which apply near the ends of the stream or at the junction of two different types of flow. The inner and outer expansions must be matched at a junction to find how the emerging flow is related to the entering flow. This process can be continued to build up any complex flow involving thin streams. The method is illustrated in the case of a wall flow that leaves the wall to become a jet, which includes the case of a waterfall treated by Clarke (1965) in a similar way. In part 2 (to be published) other inner expansions are found and matched to outer expansions, providing the ingredients for the construction of the solutions of many flow problems.

A Free-Streamline Model for Bluff Bodies in Confined Flow

1977 ◽  
Vol 99 (3) ◽  
pp. 585-592 ◽  
Author(s):  
V. J. Modi ◽  
S. E. El-Sherbiny
Keyword(s):  
Potential Flow ◽  
Bluff Body ◽  
Flow Model ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Flat Plates ◽  
Surface Loading ◽  
Confined Flow ◽  
Potential Flow Model

A potential flow model is presented for two-dimensional symmetrical bluff bodies under wall confinement. It provides a procedure for predicting surface loading on a bluff body over a range of blockage ratios. Experimental results with normal flat plates and circular cylinders for blockage ratios up to 35.5 percent substantiate the validity of the approach.

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