Pitot tube

About: Pitot tube is a research topic. Over the lifetime, 3162 publications have been published within this topic receiving 31665 citations. The topic is also known as: pitot probe.

Calibration of the Preston tube and limitations on its use in pressure gradients

Abstract: Preston's method of measuring skin friction in the turbulent boundary layer makes use of a circular Pitot tube resting on the wall. On the assumption of a velocity distribution in the wall region common to boundary layer and pipe flows the calibration curve for the Pitot tube can be obtained in fully developed pipe flow. Earlier experiments suggested that Preston's original calibration was in error, and a revised calibration curve has been obtained and is presented here.From experiments in strong favourable and adverse pressure gradients, limits are assigned to the pressure-gradient conditions within which the calibration can be used with prescribed accuracy. It is shown that in sufficiently strong favourable gradients the ‘inner-law’ velocity distribution breaks down completely, and it is suggested that this breakdown is associated with reversion to laminar flow.As an incidental result, values have been obtained for the constants occurring in the logarithmic expression for the inner-law velocity distribution.

The Determination of Turbulent Skin Friction by Means of Pitot Tubes

Abstract: A simple method of determining local turbulent skin friction on a smooth surface has been developed which utilises a round pitot tube resting on the surface. Assuming the existence of a region near the surface in which conditions are functions only of the skin friction, the relevant physical constants of the fluid and a suitable length, a universal non-dimensional relation is obtained for the difference between the total pressure recorded by the tube and the static pressure at the wall, in terms of the skin friction. This relation, on this assumption, is independent of the pressure gradient. The truth and form of the relation were first established, to a considerable degree of accuracy, in a pipe using four geometrically similar round pitot tubes—the diameter being taken as representative length. These four pitot tubes were then used to determine the local skin friction coefficient at three stations on a wind tunnel wall, under varying conditions of pressure gradient. At each station, within the limits of experimental accuracy, the deduced skin friction coefficient was found to be the same for each pitot tube, thus confirming the basic assumption and leaving little doubt as to the correctness of the skin friction so found. Pitot traverses were then made in the pipe and in the boundary layer on the wind tunnel wall. The results were plotted in two non-dimensional forms on the basis already suggested and they fell close together in a region whose outer limit represented the breakdown of the basic assumption, but close to the wall the results spread out, due to the unknown displacement of the effective centre of a pitot tube near a wall. This again provides further evidence of the existence of a region of local dynamical similarity and of the correctness of the skin friction deduced from measurements with round pitot tubes on the wind tunnel wall. The extent of the region in which the local dynamical similarity may be expected to hold appears to vary from about 1/5 to 1/20 of the boundary-layer thickness for conditions remote from, and close to, separation respectively.

Digital Particle Image Velocimetry

Abstract: Development of aerospace airframes and propulsion systems depends on the accurate simulation of these components in their normal operating environment. Measurement of velocity fields is of critical importance in these aerodynamic studies in order to both verify the external flow field and also to determine the performance of these components/systems in the flow field. Quantitative flow field measurements were initially obtained in aerodynamic studies using Pitot static probes, which were suitable for measuring the time-average or low frequency response flow field properties at a single point in the flow.1 Hot wire anemometry proved to be a significant improvement over pitot probes by providing high frequency response velocity measurements.1 Adding more wires enabled multi-component flow measurements. By their design, hot wires are very fragile and easily damaged by foreign objects or particles in the flow. While able to provide continuous records of flow fluctuations, hot wire anemometers only perform reliably in low turbulence flows. Similar to pitot probes, hot wire anemometers were invasive and disturbed the flow field under study. The first non-invasive point velocity measurement technique was Laser Doppler Velocimetry (LDV), which used a crossed pair of laser beams to measure the velocity of seed particles entrained in the flow.1

Experiments on the flow and acoustic properties of a moderate-Reynolds-number supersonic jet

Abstract: Flow and acoustic properties of a jet at Reynolds number of 70,000 were studied at Mach 2.1. Measurements in a free jet test facility were made with pitot tubes and hot-wire anemometry. Center-line Mach number distributions for natural and excited jets were obtained. A slow initial growth rate was in the potential core region of the jet, indicating a transition from laminar to turbulent flow in moderate Reynolds number jets. The transition occurred within the first 2-3 diameters. Spectral components were calculated for the fluctuating flowfield, and sound pressure levels were measured for the overall near-field noise. The centroid of noise was located about 8 nozzle diameters downstream. The growth rates of instabilities were determined to be in agreement with linear stability theory predictions over a broad frequency range.