Considerations in Exploring Laboratory Tornadolike Vortices with a Laser Doppler Velocimeter

John T. Snow College of Geosciences, University of Oklahoma, Norman, Oklahoma

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Donald E. Lund Milan, Michigan

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Abstract

A laser Doppler velocimeter was used to collect datasets consisting of means and turbulence intensities of radial and tangential velocity components for two vortex morphologies within a Ward-type tornado vortex chamber. This paper focuses on problems encountered in the application of the laboratory technique and the applied solutions. Among these are the nature and origin of particles for backscattering laser light, establishing and maintaining boundary conditions, lack of coincidence between the mean position of the vortex axis and that of the vortex chamber, and the nonstationary nature of the vortex. The impact of the axial offset and wander of the vortex on velocity measurements is examined using realistic velocity profiles based on laboratory data and parameters governing vortex wander based on video imagery. It is found that the tangential speed maximum was underestimated by at least 15% due to an inherent averaging process and that the core radius was overestimated by a factor of nearly 50%.

Corresponding author address: Dr. John T. Snow, College of Geosciences, Sarkeys Energy Center, Room 710, 100 East Boyd, Norman, OK 73019.

Abstract

A laser Doppler velocimeter was used to collect datasets consisting of means and turbulence intensities of radial and tangential velocity components for two vortex morphologies within a Ward-type tornado vortex chamber. This paper focuses on problems encountered in the application of the laboratory technique and the applied solutions. Among these are the nature and origin of particles for backscattering laser light, establishing and maintaining boundary conditions, lack of coincidence between the mean position of the vortex axis and that of the vortex chamber, and the nonstationary nature of the vortex. The impact of the axial offset and wander of the vortex on velocity measurements is examined using realistic velocity profiles based on laboratory data and parameters governing vortex wander based on video imagery. It is found that the tangential speed maximum was underestimated by at least 15% due to an inherent averaging process and that the core radius was overestimated by a factor of nearly 50%.

Corresponding author address: Dr. John T. Snow, College of Geosciences, Sarkeys Energy Center, Room 710, 100 East Boyd, Norman, OK 73019.

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