The fluctuating wall-shear stress and the velocity field in the viscous sublayer

Alfredsson, P. Henrik; Johansson, A.; Haritonidis, Joseph H.; Eckelmann, Helmut

doi:10.1063/1.866783

Cited by 281 publications

(178 citation statements)

References 21 publications

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“…However, the existence of negative shear stress events cannot be distinguished with hot wires, hence no further assessment can be made to that effect. The values of higher order moments are also shown in figure 5(a); their value being smaller than those commonly reported in the literature (S ≈ 1 and K ≈ 4.8 by (Alfredsson et al, 1988)) probably due to wireresolution effects (Talamelli et al, 2013).…”

Section: Fluctuating Shear Stress τmentioning

confidence: 55%

“…On the other hand, constant temperature anemometry enables the instantaneous value of the wall shear stress to be determined. Due to their large thermal inertia, hot films present a damping of the fluctuations in low thermal conductivity fluids (as first reported by Alfredsson et al, 1988); hence a wall-mounted hot wire will be employed due to its better frequency response.…”

Section: Introductionmentioning

confidence: 99%

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Experimental measurement of wall shear stress in strongly disrupted flows

Rodríguez-López

Bruce

Buxton

2017

Journal of Turbulence

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Mean and fluctuating wall shear stress is measured in strongly disrupted cases generated by various low-porosity wall-mounted single-and multi-scale fences. These grids generate a highly turbulent wake which interacts with the wall-bounded flow modifying the wall shear stress properties. Measurement methods are validated first against a naturally growing zero pressure gradient turbulent boundary layer showing accuracies of 1% and 4% for extrapolation and direct measurement of the mean shear stress respectively. Uncertainty associated with the root mean square level of the fluctuations is better than 2% making it possible to measure small variations originating from the different fences. Additionally, probability density functions and spectra are also measured providing further insight into the flow physics. Measurement of shear stress in the disrupted cases (grid+TBL) suggest that the flow characteristics and turbulence mechanisms remain unaltered far from the grid even in the most disrupted cases. However, a different root mean square level of the fluctuations is found for different grids. Study of the probability density functions seem to imply that there are different degrees of interaction between the inner and outer regions of the flow.

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Section: Fluctuating Shear Stress τmentioning

confidence: 55%

Section: Introductionmentioning

confidence: 99%

Experimental measurement of wall shear stress in strongly disrupted flows

Rodríguez-López

Bruce

Buxton

2017

Journal of Turbulence

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“…For example, in a study involving conventional hot-film shear stress probes, Alfredsson et al noted that using the static calibration to reduce dynamic data resulted in a significant under-prediction of the rms turbulent shear stress levels when there was substantial heat conduction to the substrate. 6 Specifically, large variations were reported in the axial turbulent wall shear stress intensity / rms w τ τ ′ . Because of the unknown dynamic response of thermal sensors, it is virtually impossible to separate errors in spatial averaging from those due to unsteady heat conduction.…”

Section: 248mentioning

confidence: 99%

“…5 Similarly, the ratio of the convective time scale to the Kolmogorov time scale ℑ τ is the wall shear stress, and ρ is the density) is often used to determine the spatial resolution performance of probes in turbulent boundary layers, the above scaling is sufficient to illustrate the stringent spatial resolution requirements for turbulent flows. 6 In addition, a flat frequency response function is desired for turbulence measurements so that the spectra and statistical moments are accurately estimated. If the required data analysis requires correlation analysis, a zero-phase frequency response function over a wide frequency range is also desirable.…”

Section: Introductionmentioning

confidence: 99%

MEMS Shear Stress Sensors: Promise and Progress

Sheplak

Cattafesta

Nishida

et al. 2004

24th AIAA Aerodynamic Measurement Technology and Ground Testing Conference

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This paper reviews existing microelectromechanical systems (MEMS)-based shear stress sensors. The promise and progress of MEMS scaling advantages to improve the spatial and temporal resolution and accuracy of shear stress measurement is critically reviewed. The advantages and limitations of existing devices are discussed. Finally, unresolved technical issues are summarized for future sensor development.

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“…Despite its advantages, in order to make this technology of practical applicability, the sensor should be insensitive to the thermal characteristics of substrate on which it is installed, and should provide a rapid response to fluctuations of shear stress [8]. In this sense several proposals emerged.…”

Section: Introductionmentioning

confidence: 99%

Wall shear stress hot film sensor for use in gases

Osorio¹,

Silin²

2011

J. Phys.: Conf. Ser.

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-The dynamic response of a hot-wire anemometer: III. Voltage-perturbation versus velocity-perturbation testing for near-wall hot-wire/film probes B C Khoo, Y T Chew, C J Teo et al. Abstract. The purpose of this work is to present the construction and characterization of a wall shear stress hot film sensor for use in gases made with MEMS technology. For this purpose, several associated devices were used, including a constant temperature feedback bridge and a shear stress calibration device that allows the sensor performance evaluation. The sensor design adopted here is simple, economical and is manufactured on a flexible substrate allowing its application to curved surfaces. Stationary and transient wall shear stress tests were carried on by means of the calibration device, determining its performance for different conditions. IntroductionThe study of shear stress on the walls that make the boundary of a flow is an area of great interest in Fluid Mechanics and Heat Transfer. However its measurement is complex and is generally limited to experimental models. The measurement of wall shear stresses is relevant when studying the drag of blunt or aerodynamic objects, the pressure drop through conduits, the convective heat transfer of surfaces exposed to flows, etc., but it can also be used to detect the passage of fluid-dynamic structures such as hairpin vortices, vortex shearing behind obstacles or large scale coherent structures. Having a good temporal resolution in this kind of devices is of great interest, one reason for this is that the fluctuations of wall shear are relevant in the understanding of the flow and its effect on walls. In turbulent flows, the fluctuations of shear stress reach values as high as 0.46 of the mean wall shear stress [6]. The second reason is that a slow sensor exposed to a turbulent flow yields average measurement values that do not agree with the mean shear stress. That is, the average introduced by a slow sensor is not satisfactory, requiring therefore a turbulent calibration, i.e. a calibration under the same turbulence intensity that will be found in the case to be measured. To avoid such difficulties, it is necessary to obtain measurements with good temporal resolution and eventually to estimate the average value a posteriori.A technique for wall shear stress measurement that stands out for its simplicity of implementation and accuracy is the use of thermal sensors. Thermal sensors are heaters whose electrical resistance is a function of temperature, which in turn depends on the convection heat transfer between the sensor and the flow. A trend evident in all the measurement techniques of wall shear stress is that the sensors have their sensing areas ever smaller in order to improve the temporal and spatial resolution. In this process of miniaturization micro-electro-mechanical systems (MEMS) manufacturing technology has played a central role in shear stress sensor technology [7]. MEMS technology is based on the same technology developed for semiconductor device fabrication and is w...

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The fluctuating wall-shear stress and the velocity field in the viscous sublayer

Cited by 281 publications

References 21 publications

Experimental measurement of wall shear stress in strongly disrupted flows

Experimental measurement of wall shear stress in strongly disrupted flows

MEMS Shear Stress Sensors: Promise and Progress

Wall shear stress hot film sensor for use in gases

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