Forces on Cylinders Near a Plane Boundary in a Sinusoidally Oscillating Fluid

1976 ◽  
Vol 98 (3) ◽  
pp. 499-503 ◽  
Author(s):  
Turgut Sarpkaya
Keyword(s):  
Reynolds Number ◽  
Least Squares ◽  
Least Squares Method ◽  
Lift Coefficient ◽  
Transverse Force ◽  
Circular Cylinders ◽  
Plane Boundary ◽  
Water Tunnel ◽  
Inertia Coefficient ◽  
Line Force

The in-line and transverse forces acting on circular cylinders placed near a plane boundary in a sinusoidally oscillating fluid in a U-shaped vertical water tunnel have been measured. The period parameter UmT/D was varied from about 2 to 40, the Reynolds number from 4000 to 25,000, and the gap between the cylinder and the plane boundary from 0.01 D to 1.0D. The drag and inertia coefficients for the in-line force have been determined through the use of the Morison’s equation and the Fourier analysis, least squares method, and a modified least squares method. The transverse force coefficients have been obtained for the forces toward the wall and away from the wall. The results show that the in-line and transverse forces could acquire very large magnitudes and give rise to serious oscillations. For very small values of the period parameter, effects of flow separation become negligible and the inertia coefficient for the in-line force and the lift coefficient for the transverse force approach those predicted by the potential theory.

scholarly journals FORCES ON ROUGH-WALLED CIRCULAR CYLINDERS

1976 ◽  
Vol 1 (15) ◽  
pp. 134 ◽  
Author(s):  
Turgut Sarpkaya
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Least Squares Method ◽  
Reynolds Numbers ◽  
Transverse Force ◽  
Circular Cylinders ◽  
Mean Square ◽  
Relative Roughness

This paper presents the results of an extensive experimental investigation of the in-line and transverse forces acting on sand-roughened circular cylinders placed in oscillatory flow at Reynolds numbers up to 1,500,000, Keulegan-Carpenter numbers up to 100, and relative roughnesses from 1/800 to 1/50. The drag and inertia coefficients have been determined through the use of the Fourier analysis and the least squares method. The transverse force (lift) has been analysed in terms of its maximum and root-mean-square values. In addition, the frequency of vortex shedding and the Strouhal number have been determined. The results have shown that all of the coefficients cited above are functions of the Reynolds number, Keulegan-Carpenter number, and the relative roughness height. The results have also shown that the effect of roughness is quite profound and that the drag coefficients obtained from tests in steady flow are not applicable to harmonic flows even when the loading is predominantly drag.

Thermal Resistance in a Rectangular Flux Channel With Nonuniform Heat Convection in the Sink Plane

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
M. Razavi ◽  
Y. S. Muzychka ◽  
S. Kocabiyik
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Least Squares ◽  
Least Squares Method ◽  
Separation Of Variables ◽  
Plane Boundary ◽  
The Heat Transfer Coefficient

In this paper, thermal resistance of a 2D flux channel with nonuniform convection coefficient in the heat sink plane is studied using the method of separation of variables and the least squares technique. For this purpose, a two-dimensional flux channel with discretely specified heat flux is assumed. The heat transfer coefficient at the sink boundary is defined symmetrically using a hyperellipse function which can model a wide variety of different distributions of heat transfer coefficient from uniform cooling to the most intense cooling in the central region. The boundary condition along the edges is defined with convective cooling. As a special case, the heat transfer coefficient along the edges can be made negligible to simulate a flux channel with adiabatic edges. To obtain the temperature profile and the thermal resistance, the Laplace equation is solved by the method of separation of variables considering the applied boundary conditions. The temperature along the flux channel is presented in the form of a series solution. Due to the complexity of the sink plane boundary condition, there is a need to calculate the Fourier coefficients using the least squares method. Finally, the dimensionless thermal resistance for a number of different systems is presented. Results are validated using the data obtained from the finite element method (FEM). It is shown that the thick flux channels with variable heat transfer coefficient can be simplified to a flux channel with the same uniform heat transfer coefficient.

An experimental investigation of the oscillating lift and drag of a circular cylinder shedding turbulent vortices

1961 ◽  
Vol 11 (2) ◽  
pp. 244-256 ◽  
Author(s):  
J. H. Gerrard
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Cylinder Surface ◽  
Fluctuating Pressure ◽  
Order Of Magnitude ◽  
Lift And Drag

The oscillating lift and drag on circular cylinders are determined from measurements of the fluctuating pressure on the cylinder surface in the range of Reynolds number from 4 × 103 to just above 105.The magnitude of the r.m.s. lift coefficient has a maximum of about 0.8 at a Reynolds number of 7 × 104 and falls to about 0.01 at a Reynolds number of 4 × 103. The fluctuating component of the drag was determined for Reynolds numbers greater than 2 × 104 and was found to be an order of magnitude smaller than the lift.

Phase-Lag-Induced Fluctuating Lift Forces on Two Tandem Bluff Bodies

2015 ◽  
Author(s):  
Md. Mahbub Alam ◽  
Ma Zhe
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Vortex Dynamics ◽  
Lift Coefficient ◽  
Nonlinear Function ◽  
Local Maximum ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Phase Lag ◽  
Spacing Ratio

A numerical simulation at a Reynolds number Re = 200 is conducted to find how flow-induced forces on two tandem circular cylinders is connected to the phase lag between vortex sheddings from the cylinders. The spacing ratio L* (= L/D) is varied from 2 to 9, where L is the cylinder center-to-center spacing and D is the cylinder diameter. Here we mainly focus on fluctuating lift coefficient CLf of the upstream cylinder, vortex dynamics in the gap between cylinders, and phase lag ϕ between the vortex sheddings from the two cylinders for L* larger than the critical where the co-shedding flow prevails. ϕ is indeed nonlinear function of L*, Strouhal number (St) and convection velocity of vortices in the gap between the cylinders. We unearth that the upstream cylinder CLf is affected by both L* and ϕ. While the contribution of L* to CLf diminishes rapidly with L*, that of ϕ makes the L*-dependent CLf variation damped-sinusoidal, persisting in the L* range examined. The inphase and antiphase flows respectively correspond to a local maximum and minimum CLf. How CLf is correlated with L* and ϕ can be deduced as, C L f = A e −α L * + B e −β L * sin ϕ + π 2 + C , where A, α, B, β and C are constants. The physics behind the damped-sinusoidal variation in CLf is discussed.

The predominant frequency for viscous flow past two tandem circular cylinders of different diameters at low Reynolds number

2019 ◽  
Vol 234 (2) ◽  
pp. 534-546
Author(s):  
Ming-ming Liu
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Viscous Flow ◽  
Lift Coefficient ◽  
Circular Cylinders ◽  
Predominant Frequency ◽  
Flow Past ◽  
Gap Ratio ◽  
The Mean ◽  
Different Diameters

Viscous flow past two circular cylinders in tandem arrangement is numerically investigated at a typical Reynolds number of 200 which is based on the diameter of the downstream cylinder. The non-dimensional diameter of the downstream cylinder D is fixed to be 1.0, while the non-dimensional diameter of the upstream cylinder d varies from 0.1 to 1.0 with an interval of 0.1. Moreover, the minimal non-dimensional distance between the two cylinders changes from 0.1 to 4.0. The numerical results show that continuous variation of the mean drag coefficient, the lift coefficient, and the lift frequency is observed with the increase in the gap ratio for d/ D = 0.1 and 0.2. Discontinuities are found for the mean drag coefficient, the lift coefficient, and the lift frequency of the downstream cylinder with the increase in gap ratio for d/ D = 0.9 and 1.0. Multiple lift oscillating frequencies of the downstream cylinder can be detected for d/ D = 0.3–0.8 at special gap ratios. Special attention is paid on d/ D = 0.4, which is a typical example for d/ D = 0.3–0.8. The predominant lift frequency of the downstream cylinder is observed to change from fL-1 to fL-2 as the increase in the gap ratio for d/ D = 0.4, which have not been previously detected. However, the predominant drag frequency of the downstream cylinder is found always to be fD-3 in present investigation scope. Moreover, a conclusion that fD-3 =  fL-1 +  fL-2 can be obtained.

Forces on Cylinders and Spheres in a Sinusoidally Oscillating Fluid

1975 ◽  
Vol 42 (1) ◽  
pp. 32-37 ◽  
Author(s):  
T. Sarpkaya
Keyword(s):  
Fourier Analysis ◽  
Reynolds Numbers ◽  
Transverse Force ◽  
Circular Cylinders ◽  
Driving Frequency ◽  
Line Force ◽  
Cylinders And Spheres

The in-line and transverse forces acting on circular cylinders and the in-line force acting on spheres immersed in a harmonically oscillating fluid in a U-shaped vertical tunnel have been measured. The drag, inertia, and the transverse force (lift) coefficients have been determined through the use of a Fourier analysis and found to depend on a period parameter. The results have shown that the transverse force on cylinders is as large as the in-line force and alternates at frequencies ranging from one to four times the driving frequency of the fluid within the range of subcritical Reynolds numbers encountered in the investigation.

In-Line and Transverse Forces on Cylinders in Oscillatory Flow at High Reynolds Numbers

1977 ◽  
Vol 21 (04) ◽  
pp. 200-216 ◽  
Author(s):  
Turgut Sarpkaya
Keyword(s):  
Oscillatory Flow ◽  
Least Squares Method ◽  
Reynolds Numbers ◽  
Transverse Force ◽  
Circular Cylinders ◽  
Relative Roughness ◽  
High Reynolds Numbers ◽  
Smooth Cylinder ◽  
New Interpretation ◽  
High Reynolds

This paper presents the results of an extensive experimental investigation of the in-line and transverse forces acting on smooth and sand roughened circular cylinders placed in oscillatory flow at Reynolds numbers up to 1.5 × 106, Keulegan Carpenter numbers up to 100, and relative roughnesses from 1/800 to 1/50. The drag and inertia coefficients have been determined through the use of the Fourier analysis and the least-squares method. The transverse force (lift) has been analyzed in terms of its maximum, semi peak-to-peak, and root-mean-squarevalues. In addition, the frequency of vortex shedding and the Strouhal number have been determined. The results have shown that (a) for smooth cylinders, all of the coefficients just cited are functions of the Reynolds and Keulegan-Carpenter numbers, particularly for Reynolds numbers larger than about 20 000; (b) for rough cylinders, the force coefficients also depend on the relative roughness k/D and differ significantly from corresponding to the smooth cylinder; and that (c) the use of the frequencyparameter' D2/vT and the roughness Reynolds number Umk/vallows a new interpretation of the present as well as the previously obtained data.

Effects of Masts on the Aerodynamics of Sail Sections

1978 ◽  
Vol 15 (01) ◽  
pp. 35-42
Author(s):  
Jerome H. Milgram
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Lift Coefficient ◽  
Limited Range ◽  
Cross Sectional Area ◽  
Water Tunnel ◽  
Two Dimensional ◽  
Sectional Area ◽  
Cross Sectional ◽  
Coefficient Versus

The effects of the addition of masts of varying geometries to two different sail-like two-dimensional airfoil sections were determined by water tunnel tests. Thirteen different mast-sail combinations were tested with four of the sections retested at a different time to confirm repeatability of the data. The results were found to be best presented and best understood by means of graphs of drag coefficient versus lift coefficient for fixed values of d/c(mast diameter/sail chord). The additional drag caused by the addition of a mast was found to be substantial, especially as the ratio d/cbecame relatively large. Results were found to be insensitive to changes in Reynolds number of a factor of two for d/cless than 0.3 for round masts, and 0.2 for elliptical masts (d for an elliptical mast is taken as the diameter of a circle having the same cross-sectional area). Elliptical masts with d/c greater than 0.3 gave results which exhibited a sensitivity to Reynolds number and which, over a limited range of lift coefficients, gave an unexpectedly high value of the ratio of lift coefficient/drag coefficient.

‘Least squares’ method—theorem or law?

1980 ◽  
Vol 59 (9) ◽  
pp. 8
Author(s):  
D.E. Turnbull
Keyword(s):  
Least Squares ◽  
Least Squares Method
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