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A new method of interpreting the signals from triple-sensor thermal anemometer probes has been developed based on fast solution for all the roots of the non-linear Jorgensen (1971) equations describing the directional response of each cylindrical sensor. The sensors can be oriented at arbitrary angles to each other, but always within a range of probe geometries that keep prong interference and thermal wake interference below acceptable levels. The properties of a class of non-orthogonal symmetric tetrahedral probe geometries are studied in relation to the range of flow vector angles that can be measured, the sensitivity of the probe with respect to changes in flow angle, and the sensitivity of the computed velocity components due to angular errors associated with the construction of the probe. The solutions of Jorgensen's equations are inherently multiple-valued, but if the velocity vector is restricted to be within a cone of angles, they are unique. It is shown that measurements with non-orthogonal triple sensor signals are sensitive to angular deviations of a few degrees of the sensor angles from the nominally orthogonal probe geometry, indicating the need of a non-orthogonal algorithm. The mean, rms, Reynolds stress, and power spectrum of the velocity in fully developed turbulent pipe flow were measured using a specially designed triple sensor probe and the proposed algorithm. [ABSTRACT FROM AUTHOR]

Measurements of the streamwise velocity over solid sinusoidal waves with height to wavelength ratios of 2 a/λ=0.05, 0.125 and with dimensionless wave numbers α=0.00624, 0.00135 have been made. For these conditions the instantaneous flow reverses direction, but the time-averaged flow is non-separated. Many features of the flow are similar to those reported in previous papers for a time-averaged flow that is separated. Approximate agreement is obtained from an eddy viscosity model derived for flow over small amplitude waves. However, the differences are more interesting than the agreement in that they point out shortcomings of present Reynolds stress models. Comparison with other measurements in the literature shows how increasing Reynolds number decreases the size of the separated region. Measurements of pressure profiles and of drag are interpreted in terms of measured flow patterns. [ABSTRACT FROM AUTHOR]

The transition from steady thermal convection to turbulent thermal convection in a horizontal layer of water (Prandtl number=5.8) contained by a square cavity of large aspect ratio (48.5) has been studied using laser Doppler velocimetry. Power spectra of the horizontal velocity fluctuations were measured in the Rayleigh number range from 30,000 and 99,000, wherein periodic, quasi-periodic, and broad-band time-dependent instabilities coexist. At Rayleigh numbers greater than 32,000 a narrow-band spectrum emerges. The frequency of this motion scales with x/d modified by a Prandtl number factor for intermediate values of the Prandtl number. Between 10 Raand 30 Rathe frequency undergoes three abrupt jumps while increasing along an Ra power law. A different frequency mode that occurs above 30 Raappears to be associated with fully turbulent convection. [ABSTRACT FROM AUTHOR]

The power spectrum and the correlation of the laser Doppler velocimeter velocity signal obtained by sampling and holding the velocity at each new Doppler burst are studied. Theory valid for low fluctuation intensity flows shows that the measured spectrum is filtered at the mean sample rate and that it contains a filtered white noise spectrum caused by the steps in the sample and hold signal. In the limit of high data density, the step noise vanishes and the sample and hold signal is statistically unbiased for any turbulence intensity. [ABSTRACT FROM AUTHOR]

Turbulence in thermal convection is investigated for flows in which the production of turbulence energy is due solely to buoyancy, and the statistics of the flow are homogeneous in horizontal planes. New experimental results for high Rayleigh number unsteady turbulent convection in a horizontal layer heated from below and insulated from above are presented and compared to turbulent Rayleigh convection, convection in the planetary boundary layer, and laboratory penetrative convection. Mean temperature fields are correlated in terms of wall layer scales and convection scales. Joint statistics of turbulent temperature and horizontal velocity and vertical velocity through fourth order are presented for the core region of the convection layer. [ABSTRACT FROM AUTHOR]