Laser Doppler Velocity Profile Sensor Research Articles

Near-wall measurements of turbulence statistics in a fully developed channel flow with a novel laser Doppler velocity profile sensor

This paper reports on the measurements of the near-wall turbulence statistics in a fully developed channel flow. The flow measurements were carried out with a novel laser Doppler velocity profile sensor with a high spatial resolution. The sensor provides both the information of velocity and position of individual tracer particles inside the measurement volume. Hence, it yields the velocity profile inside the measurement volume, in principle, without the sensor being mechanically traversed. Two sensor systems were realized with different techniques. Typically the sensor has a relative accuracy of velocity measurement of 10 −3 and the spatial resolution of a few micrometers inside the measurement volume of about 500 μm long. The streamwise velocity was measured with two independent sensor systems at three different Reynolds number conditions. The resulting turbulence statistics show a good agreement with available data of direct numerical simulations up to fourth order moment. This demonstrates the velocity profile sensor to be one of the promising techniques for turbulent flow research with the advantage of a spatial resolution more than one magnitude higher than a conventional laser Doppler technique.

Determination of the axial velocity component by a laser-Doppler velocity profile sensor

We report about the determination of the axial velocity component by a laser Doppler velocity profile sensor that is based on two superposed fanlike interference fringe systems. Evaluation of the ratio of the Doppler frequencies obtained from each fringe system yields the lateral velocity component and the axial position inside the fringe system. Inclined particle trajectories result in chirped burst signals, where the change of the Doppler frequency in one burst signal is directly related to the axial velocity component. For one single tracer particle it is possible to determine (i) the lateral velocity component, (ii) the axial velocity component including the direction, and (iii) the axial position of the tracer trajectory. In this paper we present the measurement principle and report about results from simulation and experiments. An uncertainty of the axial velocity component of about 3% and a spatial resolution in the micrometer range were achieved. Possible applications of the sensor lie in three-component velocity measurements of flow fields where only one optical access is available.

Spatial resolving laser Doppler velocity profile sensor using slightly tilted fringe systemsand phase evaluation

In this paper we report on a differential laser Doppler velocimeter which offersspatially resolved measurements in the probe volume. For the first time, twolaser wavelengths are employed to generate two interference fringe systems withidentical fringe spacing which are slightly tilted towards each other. The relativephase shift varies linearly with the position along the optical axis, thus allowingspatially resolved measurements. In the centre of the measurement volume a spatialresolution in the nanometre range is achieved. The sensor was applied in a windtunnel for the determination of the wall shear stress of a laminar flat-plate flowwithout mechanical traversing. Spatially resolved measurements of the Blasiusvelocity profile are presented. All results agree well with the theoretical prediction.