The hardware development and testing of a unique lab technique for rapidly
sampling profiles of vertical velocity and temperature in a thermally
stratified turbulent shear flow is presented. The main purpose of this
novel system is to mimic vertical measurements made by oceanographers and to
gain a better understanding of what vertical sampling in the ocean can tell
us about oceanic turbulence and mixing. The sensing elements consist of a
cold wire probe for temperature measurements and a hot wire probe for
velocity measurements. These are propelled vertically through a thermally
stratified wind tunnel by a pneumatic piston. Speeds in excess of 10 m/s
are reached as it traverses the central part of the tunnel. This speed is
sufficient to freeze the flow structure sampled by the sensors, so the
measured profiles are effectively instantaneous. The design of the vertical
traverse device consists of a pneumatic piston, a valve system, and a linear
strip encoder. A computer using LabVIEW software controls the device.
Vertical velocity and acceleration profiles of the traverse are presented to
demonstrate the dynamic characteristics and performance of the system.
Ensemble-averaged measurements of the temperature profiles are compared to
single-point time-averaged measurements to reaffirm the capability of the
profiler. The application of this apparatus to future vertical measurements
of temperature and vertical velocity and their spatial variation will allow
the study of turbulent quantities such as available potential energy,
turbulent kinetic energy, diapycnal flux, vertical one-dimensional spectra
and other quantities associated with turbulence mixing.