Flow Past Rotating Low Axis Ratio Elliptic Cylinder

The subcritical flow over an array of elliptic cylinders with an axis ratio of 1:2 was studied both experimentally and numerically. The mean velocities, turbulence levels and the vortex dynamics of the array were determined experimentally by flow visualization and using a laser Doppler anemometer (LDA) and the flow was modelled using three-dimensional large eddy simulation (LES). The experimental results were compared with results obtained previously using circular cylinders and with numerical predictions of the flow. The study indicated that the flow past such a widely spaced array is characterized by low turbulence levels and poor lateral mixing compared with conventional circular cylinder arrays, and a weak flow periodicity with a constant Strouhal number of 0.11 was detected in downstream rows. The predicted mean and r.m.s. velocities, as well as the flow periodicity, were in good agreement with the experimental results.

Download Full-text

Linear Shear Flow Past a Rotating Elliptic Cylinder

Journal of Fluids Engineering ◽

10.1115/1.4040365 ◽

2018 ◽

Vol 140 (12) ◽

Cited By ~ 4

Author(s):

Sandeep N. Naik ◽

S. Vengadesan ◽

K. Arul Prakash

Keyword(s):

Shear Flow ◽

Immersed Boundary Method ◽

Elliptic Cylinder ◽

Immersed Boundary ◽

Axis Ratio ◽

Rotation Rates ◽

Flow Past ◽

Shear Parameter ◽

Linear Shear ◽

Flow Features

Simulations are carried out for linear shear flow past a rotating elliptic cylinder to investigate the effect of shear flow on hovering vortex. An in-house fluid solver that is based on immersed boundary method (IBM) is used to study the flow features and variation in aerodynamic forces. The simulations are carried out for various nondimensional rotation rates, axis ratio (AR) of the cylinder, and shear parameter. In shear flow past rotating elliptic cylinder, the negative vortices are sustained for longer distances in the downstream of the cylinder, and due to the velocity gradient, the sequence of the vortex street changes. It also has significant effect on the formation and composition of hovering vortex. To capture these features, each vortex is tracked as they form, detach, and move in the wake of the cylinder. Hovering vortex, formed due to coalescing of multiple vortices near the cylinder, is subdued for smaller rotation rates at moderate shear. It is also observed that lift forces increase linearly with shear, while the frequency of shedding shows no dependency on shear parameter.

Download Full-text

Study of two-dimensional flow past an elliptic cylinder by discrete-vortex approximation

Seventh International Conference on Numerical Methods in Fluid Dynamics - Lecture Notes in Physics ◽

10.1007/3-540-10694-4_31 ◽

2008 ◽

pp. 212-217

Author(s):

Kiyosi Horiuti ◽

Kunio Kuwahara ◽

Yuko Oshima

Keyword(s):

Elliptic Cylinder ◽

Two Dimensional ◽

Discrete Vortex ◽

Dimensional Flow ◽

Flow Past ◽

Two Dimensional Flow

Download Full-text

Experimental and Numerical Investigation of Natural Convection Heat Transfer in Horizontal Elliptic Annuli

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1696 ◽

2008 ◽

Vol 6 (1) ◽

Author(s):

Ramadan Y. Sakr ◽

Nabil S. Berbish ◽

Ali A. Abd-Aziz ◽

Abdalla Said Hanafi

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Rayleigh Number ◽

Average Nusselt Number ◽

Orientation Angle ◽

Elliptic Cylinder ◽

Major Axis ◽

Radius Ratio ◽

Hydraulic Radius ◽

Axis Ratio

Experimental and numerical studies for natural convection in two dimensional regions formed by a constant flux heat horizontal elliptic tube concentrically located in a larger, isothermally cooled horizontal cylinder were investigated. Both ends of the annulus are closed. Experiments were carried out for the Rayleigh number based on the equivalent annulus gap length ranges from 1.12x107 up to 4.92x107; the elliptic tube orientation angle varies from 0o to 90o and the hydraulic radius ratio, HRR, was 6.4. These experiments were carried out for the axis ratio of an elliptic tube (minor/major=b/c) of 1:3. The numerical simulation for the problem is carried out by using commercial CFD code. The effects of the orientation angle as well as other parameters such as elliptic cylinder axis ratio and hydraulic radius ratio on the flow and heat transfer characteristics are investigated numerically. The numerical simulations covered a range of elliptic tube axis ratios from 0.1 to 0.98 and for the hydraulic radius ratios from 1.5 to 6.4. The results showed that the average Nusselt number increases as the orientation angle of the elliptic cylinder increases from 0o (the major axis is horizontal) to 90o (the major axis is vertical) and with the Rayleigh number as well. Also, the average Nusselt number decreases with the increase of the hydraulic radius ratio. An increase up to 1.75 and further increases in the hydraulic radius ratio leads to an increase in the average Nusselt number. The axis ratio of the elliptic cylinder has an insignificant effect on the average Nusselt number. Both the average and local Nusselt number from the experimental results are compared with those obtained from the CFD code.Both the fluid flow and heat transfer characteristics for different operating and geometric conditions are illustrated velocity vectors and isotherm contours that were obtained from the CFD code. Also, two correlation equations that relate the average Nusslet number with the Rayleigh number, orientation angle, and hydraulic radius ratio and axis ratio are obtained.

Download Full-text

Erratum: “Application of the Thin-Wing-Expansion Method to the Compressible Flow past an Elliptic Cylinder”

Journal of the Physical Society of Japan ◽

10.1143/jpsj.9.145 ◽

1954 ◽

Vol 9 (1) ◽

pp. 145-145

Author(s):

Hidenori Hasimoto

Keyword(s):

Compressible Flow ◽

Elliptic Cylinder ◽

Expansion Method ◽

Thin Wing ◽

Flow Past

Download Full-text

Flow Around an Elliptic Cylinder in the Critical Reynolds Number Regime

Journal of Fluids Engineering ◽

10.1115/1.3242635 ◽

1987 ◽

Vol 109 (2) ◽

pp. 149-155 ◽

Cited By ~ 33

Author(s):

T. Ota ◽

H. Nishiyama ◽

Y. Taoka

Keyword(s):

Reynolds Number ◽

Strouhal Number ◽

Critical Reynolds Number ◽

Separation Bubble ◽

Leading Edge ◽

Elliptic Cylinder ◽

Reynold Number ◽

Major Axis ◽

Cylinder Surface ◽

Axis Ratio

Flow around an elliptic cylinder of axis ratio 1:3 has been investigated experimentally in the critical Reynolds number regime on the basis of mean static pressure measurements along the cylinder surface and of hot-wire velocity measurements in the near wake. The critical Reynold number has been found to vary with the angle of attack α and attains a minimum around α = 5 to 10 deg. At the critical Reynolds number, the drag, lift, and moment coefficients change discontinuously, and the Strouhal number based on the upstream uniform flow velocity and the major axis length of the cylinder reaches a maximum of about 1.0 to 1.5 depending on α. It is found, however, that the universal Strouhal number based on the velocity along the separated shear layer and the wake width is nearly equal to 0.19, on average, even in the critical Reynolds number regime. The pressure distribution along with the surface oil flow pattern revealed the existence of a small separation bubble near the leading edge accompanying a turbulent boundary layer.

Download Full-text

A new method of solving Oseen’s equations and its application to the flow past an inclined elliptic cylinder

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1954.0148 ◽

1954 ◽

Vol 224 (1157) ◽

pp. 141-160 ◽

Cited By ~ 29

Keyword(s):

Reynolds Number ◽

Elliptic Cylinder ◽

Cylindrical Body ◽

Thickness Ratio ◽

Successive Approximations ◽

Angle Of Incidence ◽

Mathieu Functions ◽

Flow Past ◽

Transcendental Functions ◽

Lift And Drag

In this paper is developed a general method of solving Oseen’s linearized equations for a two-dimensional steady flow of a viscous fluid past an arbitrary cylindrical body. The method is based on the fact that the velocity in the neighbourhood of the cylinder can be generally expressed in terms of a pair of analytic functions, the determination of which from the appropriate boundary condition can be effected by successive approximations in powers of the Reynolds number, R . The method enables one to obtain the velocity distribution near the cylinder and the lift and drag acting on it in the form of power series in R , without recourse to manipulation of higher transcendental functions such as Bessel and Mathieu functions for circular and elliptic cylinders, respectively. As an example of the application of the method, the uniform flow past an elliptic cylinder at an arbitrary angle of incidence is considered. Analytical expressions for the lift and drag coefficients are obtained, which are correct to the order of R , the lowest order terms being O ( R -1 ) and numerical calculations are carried out for the thickness ratio t = 0, 0.1, 0.5, 1 and the Reynolds number R = 0.1, 1. It is found that drag increases slightly with increase of either thickness ratio or angle of incidence, and that lift decreases with increase of thickness ratio while, as a function of the angle of incidence, it has a maximum at about 45°.

Download Full-text

Effect of Axis Ratio on Fluid Flow Around an Elliptic Cylinder—A Numerical Study

Journal of Fluids Engineering ◽

10.1115/1.4024862 ◽

2013 ◽

Vol 135 (11) ◽

Cited By ~ 11

Author(s):

S. Kalyana Raman ◽

K. Arul Prakash ◽

S. Vengadesan

Keyword(s):

Fluid Flow ◽

Drag Coefficient ◽

Strouhal Number ◽

Vortex Shedding ◽

Numerical Study ◽

Elliptic Cylinder ◽

Solid Boundary ◽

Axis Ratio ◽

Moderate Reynolds Number ◽

Wake Formation

The bluff body simulations over canonical forms like circular and square cylinders are very well studied and the correlations for bulk parameters like mean drag coefficient and Strouhal numbers for the same are reported widely. In the case of elliptic cylinder, the literature is very sparse, especially for moderate Reynolds number (Re). Hence, in this work, a detailed study about fluid flow characteristics over an elliptic cylinder placed in a free stream is performed. Simulations are carried out for different Re ranging from 50 to 500 with axis ratio (AR) varied between 0.1 to 1.0 in steps of 0.1. Immersed boundary method is used for the solid boundary condition implementation which avoids the grid generation for each AR and a single Cartesian grid is used for all the simulations. The effect of AR for various Reynolds numbers is also focused on using the in-house code. The influence of AR is phenomenal for all the Re and the values of wake length, drag coefficient, and Strouhal number decrease with decreasing AR for a particular Re. The critical ARs, for vortex shedding and wake formation, are identified for various Re. Detailed correlations for wake length, critical ARs for vortex shedding and wake formation, mean drag coefficient and Strouhal number, in terms of AR, are reported in this work.

Download Full-text