B. H. Lakshmana Gowda

Eccentric Drain Port to Prevent Vortexing During Draining from Cylindrical Tanks

D URING draining of liquid from a circular tank through an axisymmetrically placed circular orifice (drain port), a vortex with an air core forms as the free surface level reaches a critical height Hc. The vortex extends to the bottom port, reducing the effective cross-sectional area of the drain outlet and, consequently, the flow rate [1–4]. The presence of initial rotation can augment the vortex formation, and the flow rate can be further affected [1]. This phenomenon has practical relevance in the fuel feed system in space vehicles and rockets. Because of environmental disturbances, rotational motion can be generated in the liquid-propellant tank, which can in turn affect the rate of outflow to the engines. Attempts have been made to suppress vortexing using different methods. Baffles were used by Abramson et al. [1] to suppress sloshing, which also prevented vortexing. Ramamurthi and Tharakan [4] used a stepped drain port to arrest vortex formation. Even with initial rotation present in the liquid column, Gowda [5] showed that vortexing can be avoided by using tanks of square and rectangular cross sections. Gowda et al. [6] used a dish-type suppressor to prevent vortexing. Gowda and Udhayakumar [7] showed vane-type suppressor to be effective in preventing the vortex formation. In the present study, it is shown that evenwith initial rotation given to the liquid column, vortexing can be prevented by using eccentric drain holes. The study is carried out with different values of eccentricity parameter e=R.

Interference effects on the flow-induced vibrations of a circular cylinder in side-by-side and staggered arrangement

This paper presents the results of an investigation on the interference effects of a rigid circular cyclinder on the transverse vibrations of a spring-mounted circular cylinder (test cylinder) exposed to a uniform flow. All tests were at a single value of the reduced velocity, viz., 7·0. The interference effects were studied for the side-by-side arrangement and staggered arrangement. Experiments have been carried out for various relative dimensions of the test cylinder and the interfering cylinder; the tests for the staggered arrangement were conducted for several gap widths between the two. The results indicate that there is a critical combination of relative dimensions and spacing which gives rise to maximum amplitudes of vibration. A tentative explanation is offered for the observed features based on flow-visualization studies.

Reverse flow in a channel with an obstruction at the entry

In this study the flow through and around a parallel-walled channel with an obstruction (flat plate) placed at the channel inlet is investigated. Depending on the position of the obstruction, the flow inside the channel is in a direction opposite to that outside, stagnant or in the same direction as outside but with reduced magnitude. Flow visualization in water is used to examine the fluid motion, although some wind tunnel measurements have been made and are also reported. The parameters that have been varied are the gap between the obstruction and the entry to the channel, the length of the channel and the Reynolds number. The maximum value of the reverse flow velocity is found to be about 20% of that of the flow outside. The maximum forward velocity inside the channel (when it occurs) is only about 65% of the outside velocity even for very large gaps between the obstruction and the channel entrance. A tentative explanation is offered for the observed features.

Reverse flow in channel-influence of obstruction geometry

In the present study the flow through and around a parallel walled channel with various obstruction geometries placed at the channel entry is investigated. The flow inside the channel is found to be either stagnant, reverse, or in the forward direction depending upon the position of the obstruction. Experiments were carried out with various obstruction geometries like square, triangular, circular and semi-circular to study the effect of the shape of the geometry on the reverse flow phenomenon. Of the four, the triangular geometry gave the maximum reverse flow. The square and the semi-circular gave almost the same as the flat plate. The maximum forward flow also depends upon the shape of the obstruction geometry. To study the effect of the afterbody length the rectangular shape was chosen and models of different afterbody lengths were investigated. It is seen that the shorter afterbody lengths give a higher reverse flow. The maximum forward flow velocity however is higher for larger afterbody lengths.

REVERSE FLOW IN CHANNEL-EFFECT OF FRONT AND REAR OBSTRUCTIONS

The occurrence of reverse flow in a channel when a bluff body is kept at the entry is already known. In the earlier investigations, attention was focused on the generation of the reverse flow with bluff bodies, such as flat plate and other geometries, having the same width as the channel. The separation of the shear layers from the obstruction at the front end and the interaction of the shear layers at the rear end are mainly responsible for the reverse flow. To gain further insight into the phenomenon, the effects of the width of the obstruction at the front and that of placing another at the rear end in tandem with the front one are examined in this study. It is observed that the reverse flow occurs even when the width of the flat plate (b) is less than the channel width (w); the lower limit being b/w=0.6. At this b/w the reverse flow velocity is small, but it increases progressively with b/w until a maximum of about 30% of the forward velocity is attained for b/w≥2.0. However, reverse flow as high as 0.6 times the free‐stream velocity is obtained when another plate is kept close to the rear end in addition to the front plate. Further increase in the reverse flow to 0.83 times the free‐stream velocity has been achieved by replacing the flat plate model at the rear with a semicircular scoop.

Vortex induced oscillatory response of a circular cylinder due to interference effects

Abstract The oscillatory response of a spring mounted circular cylinder (test cylinder, diameter D) due to the presence of a rigid circular cylinder (interfering cylinder, diameter d) are presented in this paper. Ratios of d/D = 0.5, 1.0, 1.5 and 2.0 have been utilized for this purpose. Various relative positions of the test cylinder and the interfering cylinder in the tandem, side-by-side and the staggered arrangements are considered. The results show that under certain combinations of d/D ratio and the relative position, the test cylinder can experience oscillatory amplitudes nearly three times those observed for the no-interfering case. Under certain other conditions the vibrations are completely suppressed. The observed features are discussed with reference to earlier related studies.

An experimental investigation of separating flow on a convex surface

The mean and turbulent characteristics of an incompressible turbulent boundary layer developing on a convex surface under the influence of an adverse pressure gradient are presented in this paper.

Laminar flow through slots

Laminar flow through slots is investigated using a flow-visualization technique and the numerical solution of the Navier-Stokes equations for steady flow. In the flow situation studied here, the fluid enters an upper channel blocked at the rear end and leaves through a lower channel blocked at the front end. The two channels are interconnected by one, two and three slots. The flow-visualization technique effectively brings out the various features of the flow through slot(s). The ratio of the slot width to the channel height w/h is varied between 0.5 to 4.0 and the Reynolds number Re, based on the velocity at the entry to the channel and the height of the channel, is varied between 300 and 2000. Both w/h and Re influence the flow in general and the extent of the regions of recirculating flow in particular. The Reynolds number at which the vortex shedding begins depends on w/h. Computations are carried out using the computer code 2/E/FIX of Pun & Spalding (1977). The computed flow patterns closely resemble the observed patterns at various Reynolds numbers investigated except around the Reynolds number where the vortex shedding begins.