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- Author or Editor: C. R. Church x
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Abstract
Time-dependent features of the wall static pressure field beneath vortices modeled in a Ward-type vortex simulator have been investigated with emphasis on measurements of maximum surface pressure deficit. A pressure-measuring system was devised for this purpose which is capable of resolving important transient features of the surface pressure field in an essentially undistorted form, and measurement techniques were employed which reduced the influence of vortex wander. Measurements of maximum surface pressure deficits and their dependence on flow rate and geometry are presented, as well as a detailed study of the magnitudes of the maximum surface pressure deficits as a function of swirl ratio. Also presented are surface pressure distributions in individual subsidiary vortices in a multiple vortex flow.
The greatest deficit pressures are found to be associated with the penetration of the vortex breakdown to the surface. The magnitude of the surface pressure deficit is closely related to the. square of the mean vertical velocity of the upflow and also is dependent on swirl ratio. The pressure deficits in the subsidiary vortices presented are variable but range up to three times that found at the center of the “parent” vortex.
Abstract
Time-dependent features of the wall static pressure field beneath vortices modeled in a Ward-type vortex simulator have been investigated with emphasis on measurements of maximum surface pressure deficit. A pressure-measuring system was devised for this purpose which is capable of resolving important transient features of the surface pressure field in an essentially undistorted form, and measurement techniques were employed which reduced the influence of vortex wander. Measurements of maximum surface pressure deficits and their dependence on flow rate and geometry are presented, as well as a detailed study of the magnitudes of the maximum surface pressure deficits as a function of swirl ratio. Also presented are surface pressure distributions in individual subsidiary vortices in a multiple vortex flow.
The greatest deficit pressures are found to be associated with the penetration of the vortex breakdown to the surface. The magnitude of the surface pressure deficit is closely related to the. square of the mean vertical velocity of the upflow and also is dependent on swirl ratio. The pressure deficits in the subsidiary vortices presented are variable but range up to three times that found at the center of the “parent” vortex.
Abstract
The wall static pressure fields beneath tornado-like vortices have been investigated using a large vortex generator especially designed to model tornado cyclone airflow. Presented in nondimensional form, the data include both a series of radial profiles across the mean pressure field under a variety of flow conditions, and a detailed investigation of the magnitude of the central pressure as a function of swirl. The profiles clearly show the development of the intense vortical core from the no-swirl state, and the evolution of the core from a one-celled into a two-celled flow. For the experimental range examined, it is found that the greatest pressure deficits and largest pressure gradients (in the mean field) are associated with single-celled vortices. Strong evidence is found for the existence of a dynamically induced downdraft in the two-celled vortex.
Abstract
The wall static pressure fields beneath tornado-like vortices have been investigated using a large vortex generator especially designed to model tornado cyclone airflow. Presented in nondimensional form, the data include both a series of radial profiles across the mean pressure field under a variety of flow conditions, and a detailed investigation of the magnitude of the central pressure as a function of swirl. The profiles clearly show the development of the intense vortical core from the no-swirl state, and the evolution of the core from a one-celled into a two-celled flow. For the experimental range examined, it is found that the greatest pressure deficits and largest pressure gradients (in the mean field) are associated with single-celled vortices. Strong evidence is found for the existence of a dynamically induced downdraft in the two-celled vortex.
Abstract
No Abstract Available.
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Abstract
The investigation of tornado vortex dynamics by means of a laboratory simulation is described. Based on observations from nature and an examination of the Navier-Stokes equations, a laboratory simulator of the Ward type has been constructed. This simulator generates various vortex configurations as a function of swirl ratio, radial Reynolds number and aspect ratio. Configurations which are described are 1) a single laminar vortex; 2) a single vortex with breakdown bubble separating the upper turbulent region from the lower laminar region; 3) a fully developed turbulent core, where the breakdown bubble penetrates to the bottom of the experimental chamber; 4) vortex transition to two intertwined helical vortices; and 5) examples of higher order multiple-vortex configurations that form in the core region.
Hot-film anemometry measurements of the magnitude of the velocity vector and inflow (swirl) angle have been obtained in a sequence of flows characterized by progressively increasing values of swirl ratio. These data include measurements in both the quasi-irrotational outer flow and the more complex core region. Due to the similarity that exists between the model and tornadoes, these observations provide insight into the flow fields likely to be encountered in real events.
Particularly significant findings include the mapping of the transition points at which the flow converts from a single to a double helical vortex configuration, and from a double to a triple pattern, as a function of system parameters. Additionally, the velocity measurements show the development of a cylindrical shear zone at the outer edge of the core, which, through inertial instability, may lead to the multiple-vortex phenomenon.
Abstract
The investigation of tornado vortex dynamics by means of a laboratory simulation is described. Based on observations from nature and an examination of the Navier-Stokes equations, a laboratory simulator of the Ward type has been constructed. This simulator generates various vortex configurations as a function of swirl ratio, radial Reynolds number and aspect ratio. Configurations which are described are 1) a single laminar vortex; 2) a single vortex with breakdown bubble separating the upper turbulent region from the lower laminar region; 3) a fully developed turbulent core, where the breakdown bubble penetrates to the bottom of the experimental chamber; 4) vortex transition to two intertwined helical vortices; and 5) examples of higher order multiple-vortex configurations that form in the core region.
Hot-film anemometry measurements of the magnitude of the velocity vector and inflow (swirl) angle have been obtained in a sequence of flows characterized by progressively increasing values of swirl ratio. These data include measurements in both the quasi-irrotational outer flow and the more complex core region. Due to the similarity that exists between the model and tornadoes, these observations provide insight into the flow fields likely to be encountered in real events.
Particularly significant findings include the mapping of the transition points at which the flow converts from a single to a double helical vortex configuration, and from a double to a triple pattern, as a function of system parameters. Additionally, the velocity measurements show the development of a cylindrical shear zone at the outer edge of the core, which, through inertial instability, may lead to the multiple-vortex phenomenon.
