aaditya chandel | Indian institute of Technology Madras (original) (raw)
Papers by aaditya chandel
Acta Mechanica, 2021
This paper reports the experimental investigations of the wake of a rotating and translating sphe... more This paper reports the experimental investigations of the wake of a rotating and translating sphere in the close proximity of a plane wall at moderate Reynolds numbers (Re 450-2020, defined based on velocity of translation and diameter of the sphere) and for a non-dimensional rotation rate, * (ratio of surface velocity to the translation velocity of the sphere), of 1. For the current gap (h)-to-diameter (d) ratio of the sphere (h/d 1/16), at Re 1000, hairpin vortices shed in the wake where looping of small-scale vortices increases with the increase in Re. At Re > 1000, the transition from hairpin type to shear layer vortex shedding occurs. At a relatively high Reynolds number (Re 1130), the separated vortex sheets from both sides of the sphere exhibit Kelvin-Helmholtz instability, and the wake shows multiple vortical structures. At Re 2020, a strong interaction of vortex rings in the wake of the sphere and boundary layer at plane wall results in the breakdown of larger vortical structures into smaller scales. The separation angle changes from the equatorial region to the pole of the sphere because of differential rotational speeds at other planes. At midplane, the separation angle increases with Re, and it decreases again when hairpin-shear layer vortex shedding transition occurs. The Strouhal number as a function of Re indicates the presence of dual frequency beyond this transition.
Acta Mechanica, 2021
The unsteady wake of a rotating and translating sphere is experimentally investigated at Reynolds... more The unsteady wake of a rotating and translating sphere is experimentally investigated at Reynolds numbers (Re) ranging from 115 to 550 for two rotational speeds. Non-dimensional rotational speed, * , is defined as the ratio of the maximum azimuthal speed of the sphere and the speed of translation. Motion of the sphere is generated using a specially designed mechanism in a channel, and its wake has been visualized using fluorescent dye. Unlike the steady flow past a stationary sphere where the limiting Reynolds number is 270, the flow becomes unsteady when sufficient rotation rate is introduced at much lower Reynolds number (Re 115, * 0.375). The transition from one-sided to double-sided hairpin vortex occurs at one critical Re for a given rotational speed, and it switches back to one-sided hairpin vortex shedding at another critical Re. Particle image velocimetry results demonstrate the vorticity distribution in the wake and the variation of the wake width with axial distance. At very low Re, velocity profiles in the wake are nearly self-similar. The strength of the vortex rings weakens in the far wake. The decay of centerline velocity in axial direction confirms the dissipation of the vorticity in the far wake. In this unsteady flow, the time-averaged value of the separation angle is higher than that of the steady flow on the advancing side due to enhanced adverse pressure gradient. The Strouhal number calculated from the dye visualization in this range of * and Re varies from 0.175 to 0.25, a clear increasing trend both with increasing Re and *. The coefficient of drag evaluated at the center plane remains constant at 0.94 for the present investigation up to Re 550. The wavelength of the unstable hairpin vortices is found to scale inversely with the translational velocity of the sphere.
Acta Mechanica, 2021
This paper reports the experimental investigations of the wake of a rotating and translating sphe... more This paper reports the experimental investigations of the wake of a rotating and translating sphere in the close proximity of a plane wall at moderate Reynolds numbers (Re 450-2020, defined based on velocity of translation and diameter of the sphere) and for a non-dimensional rotation rate, * (ratio of surface velocity to the translation velocity of the sphere), of 1. For the current gap (h)-to-diameter (d) ratio of the sphere (h/d 1/16), at Re 1000, hairpin vortices shed in the wake where looping of small-scale vortices increases with the increase in Re. At Re > 1000, the transition from hairpin type to shear layer vortex shedding occurs. At a relatively high Reynolds number (Re 1130), the separated vortex sheets from both sides of the sphere exhibit Kelvin-Helmholtz instability, and the wake shows multiple vortical structures. At Re 2020, a strong interaction of vortex rings in the wake of the sphere and boundary layer at plane wall results in the breakdown of larger vortical structures into smaller scales. The separation angle changes from the equatorial region to the pole of the sphere because of differential rotational speeds at other planes. At midplane, the separation angle increases with Re, and it decreases again when hairpin-shear layer vortex shedding transition occurs. The Strouhal number as a function of Re indicates the presence of dual frequency beyond this transition.
Bulletin of the American Physical Society, 2018
Acta Mechanica, 2021
This paper reports the experimental investigations of the wake of a rotating and translating sphe... more This paper reports the experimental investigations of the wake of a rotating and translating sphere in the close proximity of a plane wall at moderate Reynolds numbers (Re 450-2020, defined based on velocity of translation and diameter of the sphere) and for a non-dimensional rotation rate, * (ratio of surface velocity to the translation velocity of the sphere), of 1. For the current gap (h)-to-diameter (d) ratio of the sphere (h/d 1/16), at Re 1000, hairpin vortices shed in the wake where looping of small-scale vortices increases with the increase in Re. At Re > 1000, the transition from hairpin type to shear layer vortex shedding occurs. At a relatively high Reynolds number (Re 1130), the separated vortex sheets from both sides of the sphere exhibit Kelvin-Helmholtz instability, and the wake shows multiple vortical structures. At Re 2020, a strong interaction of vortex rings in the wake of the sphere and boundary layer at plane wall results in the breakdown of larger vortical structures into smaller scales. The separation angle changes from the equatorial region to the pole of the sphere because of differential rotational speeds at other planes. At midplane, the separation angle increases with Re, and it decreases again when hairpin-shear layer vortex shedding transition occurs. The Strouhal number as a function of Re indicates the presence of dual frequency beyond this transition.
Acta Mechanica, 2021
The unsteady wake of a rotating and translating sphere is experimentally investigated at Reynolds... more The unsteady wake of a rotating and translating sphere is experimentally investigated at Reynolds numbers (Re) ranging from 115 to 550 for two rotational speeds. Non-dimensional rotational speed, * , is defined as the ratio of the maximum azimuthal speed of the sphere and the speed of translation. Motion of the sphere is generated using a specially designed mechanism in a channel, and its wake has been visualized using fluorescent dye. Unlike the steady flow past a stationary sphere where the limiting Reynolds number is 270, the flow becomes unsteady when sufficient rotation rate is introduced at much lower Reynolds number (Re 115, * 0.375). The transition from one-sided to double-sided hairpin vortex occurs at one critical Re for a given rotational speed, and it switches back to one-sided hairpin vortex shedding at another critical Re. Particle image velocimetry results demonstrate the vorticity distribution in the wake and the variation of the wake width with axial distance. At very low Re, velocity profiles in the wake are nearly self-similar. The strength of the vortex rings weakens in the far wake. The decay of centerline velocity in axial direction confirms the dissipation of the vorticity in the far wake. In this unsteady flow, the time-averaged value of the separation angle is higher than that of the steady flow on the advancing side due to enhanced adverse pressure gradient. The Strouhal number calculated from the dye visualization in this range of * and Re varies from 0.175 to 0.25, a clear increasing trend both with increasing Re and *. The coefficient of drag evaluated at the center plane remains constant at 0.94 for the present investigation up to Re 550. The wavelength of the unstable hairpin vortices is found to scale inversely with the translational velocity of the sphere.
Acta Mechanica, 2021
This paper reports the experimental investigations of the wake of a rotating and translating sphe... more This paper reports the experimental investigations of the wake of a rotating and translating sphere in the close proximity of a plane wall at moderate Reynolds numbers (Re 450-2020, defined based on velocity of translation and diameter of the sphere) and for a non-dimensional rotation rate, * (ratio of surface velocity to the translation velocity of the sphere), of 1. For the current gap (h)-to-diameter (d) ratio of the sphere (h/d 1/16), at Re 1000, hairpin vortices shed in the wake where looping of small-scale vortices increases with the increase in Re. At Re > 1000, the transition from hairpin type to shear layer vortex shedding occurs. At a relatively high Reynolds number (Re 1130), the separated vortex sheets from both sides of the sphere exhibit Kelvin-Helmholtz instability, and the wake shows multiple vortical structures. At Re 2020, a strong interaction of vortex rings in the wake of the sphere and boundary layer at plane wall results in the breakdown of larger vortical structures into smaller scales. The separation angle changes from the equatorial region to the pole of the sphere because of differential rotational speeds at other planes. At midplane, the separation angle increases with Re, and it decreases again when hairpin-shear layer vortex shedding transition occurs. The Strouhal number as a function of Re indicates the presence of dual frequency beyond this transition.
Bulletin of the American Physical Society, 2018