Obtaining accurate mean velocity measurements in high Reynolds number turbulent boundary layers using Pitot tubes

Abstract

This article reports on one component of a larger study on measurement of the zeropressure-gradient turbulent flat plate boundary layer, in which a detailed investigation was conducted of the suite of corrections required for mean velocity measurements performed using Pitot tubes. In particular, the corrections for velocity shear across the tube and for blockage effects which occur when the tube is in close proximity to the wall were investigated using measurements from Pitot tubes of five different diameters, in two different facilities, and at five different Reynolds numbers ranging from Re θ = 11 100 to 67 000. Only small differences were found amongst commonly used corrections for velocity shear, but improvements were found for existing nearwall proximity corrections. Corrections for the nonlinear averaging of the velocity fluctuations were also investigated, and the results compared to hot-wire data taken as part of the same measurement campaign. The streamwise turbulence-intensity correction was found to be of comparable magnitude to that of the shear correction, and found to bring the hot-wire and Pitot results into closer agreement when applied to the data, along with the other corrections discussed and refined here.

Assessment of uncertainties in hot-wire anemometry and oil-film interferometry measurements for wall-bounded turbulent flows

“…, for i = 1, 2, · · · , N , and V denotes the covariance matrix of parameters q. This approach was used by Bailey et al [3] to study uncertainties in zero-pressure-gradient TBL measurements using Pitot tubes, and by Hösgen et al [16] to assess uncertainties in hot-wire measurements. Linearisation can be avoided by employing sampled-based methods, in which PDFs of the QoIs are constructed by evaluation of the model response at sufficiently large numbers of realizations q (j) , randomly sampled from the joint PDF of the parameters, ρ Q (q), which is known either from a prior analysis of the measurements or by employing Bayesian techniques.…”

“…Hence, this error can be modelled through the different approaches reviewed in Section 2.3. Although we do not study the influence of the bias in the present analysis, one way to detect sources of bias would be to compare measurements of the same flow case from various facilities, performed by different researchers, as in the International Collaboration on Experimental Turbulence (ICET) described in Bailey et al [3]. There are essentially two types of bias errors: the ones associated to the mathematical model, and those present in the measurements.…”

Turbulent boundary layer statistics at very high Reynolds number

“…As for the NSTAP measurements, the initial wall distance of the Pitot probe y 0 was measured using a depth-measuring optical microscope and the probe was traversed in the wall-normal direction using a stepper motor traverse with a resolution of 0.05 µm. The Pitot tube measurements were corrected following Bailey et al (2013), including the static tap correction by McKeon et al (2003), viscous and shear corrections by Zagarola & Smits (1998), and the near-wall correction by MacMillan (1957). The data for wall distances smaller than 2d p were neglected, as in the pipe flow experiments described by Bailey et al (2014).…”

Boundary Layer Investigation at the Inlet of a Linear Blade Cascade

“…[18]. These corrections (viscous and turbulence corrections) were not used in this paper because of experimental setup.…”