Hot Wire in Wall Proximity

Janke, Gerd

doi:10.1007/978-3-642-83045-7_55

Cited by 12 publications

(8 citation statements)

References 6 publications

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“…Hutchins [9] shows a comparison of the velocity in the viscous sublayer for different wall materials. This plot is shown in Figure 5.18, where data collected by Hutchins (non-labeled) is compared with that from other studies [10][11][12][13]. In this plot, as the hot-wire probe gets closer to the wall, the velocity departs the expected linear trend (Equation 2.3) and has an apparent increase in velocity.…”

Section: Hot Wire Anemometry (Hwa)mentioning

confidence: 91%

Turbulent Boundary Layer over a Piezoelectrically Excited Traveling Wave Surface

Musgrave

Tarazaga

2019

AIAA Scitech 2019 Forum

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Skin friction drag plays a significant role in determining the fuel efficiency of a vehicle. Reducing the skin friction thus has implications in a number of applications such as aircraft, ships, and automobiles. In recent years, a large amount of studies have researched various active drag reduction methods. One particular method involves active wall motion with the use of spanwise traveling waves. These out-of-plane traveling waves interact with the vortices in the turbulent boundary layer and weaken the bursting events that are responsible for increased skin friction drag. Computational and experimental studies have shown that these spanwise traveling waves are able to reduce the skin friction by upwards of 13% in turbulent flow. However, previous studies generated traveling waves using bulky actuation setups requiring arrays of discrete actuators that limited the achievable bandwidth and traveling wave patterns. In order for traveling waves to be a practical drag reduction method, a more implementable wave generation method is necessary. A promising traveling wave generation method is known as two-mode excitation. This technique takes advantages of a surface's inherent structural properties to generate steady-state traveling waves in an open-loop fashion. In addition, the waves can be excited at most frequencies and using a small number of low-profile piezoelectric actuators. Previous research into two-mode excitation has primarily focused on one-dimensional beams. Traveling waves have been generated on a two-dimensional surface, but this was done from a fundamental standpoint with the resultant waves propagating in arbitrary directions. Before the two-mode excitation method can be applied for drag reduction, traveling waves must be generated on two-dimensional surfaces with tailorable propagation patterns. The goal of this research is the development and testing of an implementable traveling wave generation method that alters the turbulent boundary layer with the aim of reducing skin friction drag. The first objective is to further develop the two-mode excitation method in order to tailor the traveling waves generated on a two-dimensional plate. Then, these tailored traveling waves are experimentally tested to determine their effect on the turbulent boundary layer. By directly investigating the boundary layer, a more fundamental approach is taken than only focusing on the skin friction drag. Finally, the overall effect of the traveling waves on the boundary layer are compared with standing waves. vii None of this would have been possible without the support of my family. My parents, Robert and Jacqueline, you raised me to be the person I am today. You have always been there with support and encouragement, and I am eternally grateful. I want to thank my brothers, Brian and Robert, and their wives, Katie and Lindsay. You are always there to chat and you provided many late nights of fun. Finally, I want to thank Alexis Gushiken and the endless support she has given. You always know when to motivate, encourage, o...

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Section: Hot Wire Anemometry (Hwa)mentioning

confidence: 91%

Turbulent Boundary Layer over a Piezoelectrically Excited Traveling Wave Surface

Musgrave

Tarazaga

2019

AIAA Scitech 2019 Forum

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“…This reveals a dependence on the wire diameter and therefore the deviation in wire readings increases with increasing wire diameter for a constant overheat ratio. Hence the effect of the wire diameter cannot be neglected since it exerts a significant influence on the velocity and the temperature fields near the wall, see, e.g., Durst et al [1], Oka and Kostic [24], Hebbar [25], Krishnamoorthy et al [6], Janke [3] and Chew et al [13]. This dependence was also observed in [23] and [7].…”

Section: Experimental Results For Heat-conducting and Heat-insulatingmentioning

confidence: 64%

“…He recommended the corrections for the mean velocity in turbulent flow to be half of the corresponding laminar flow's correction, but without a physical interpretation for this suggestion. In contrast, it was observed by Janke [3] that the mean velocity corrections needed in turbulent flows are still the same as in laminar flows. After Wills [2], Polyakov and Shindin [4] revisited the hot-wire peculiarities near walls of different thermal conductivities (steel, copper and textolite).…”

Section: Summary Of Existing Knowledgementioning

confidence: 75%

The physics of heat transfer from hot wires in the proximity of walls of different materials

Zanoun

Durst

Shi

2009

International Journal of Heat and Mass Transfer

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“…Here, we assume as in the experiments that the voltage-velocity relation exhibited by the hot-wire holds equally well across the boundary layer flow. However, this does not necessarily hold when the hot-wire is in close proximity to the wall (e.g., Janke, 1987). Hence, we limit our analysis to the z + > 10 region, where U profiles from differing wall thermal characteristics show collapse (Hutchins & Choi, 2002), and therefore we expect minimal influence of the wall on the hot-wire voltage-velocity relation in this region.…”

Section: Modelling the Hot-wire Calibrationmentioning

confidence: 99%

Sensitivity of turbulent stresses in boundary layers to cross-wire probe uncertainties in the geometry and calibration procedure

Baidya

Philip

Hutchins

et al. 2019

Meas. Sci. Technol.

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The sensitivity of measured turbulent stresses to uncertainties in the probe geometry and calibration procedure is investigated for a cross-wire probe in a turbulent boundary layer using direct numerical simulation (DNS) data. The errors investigated are guided by experiments, and to replicate the full experimental procedure, the cross-wire calibration procedure is simulated to generate a voltage-tovelocity mapping function, which is then utilised to calculate the measured velocity from simulated cross-wire voltages. We show that wire misalignment can lead to an incorrect mean wall-normal velocity and Reynolds shear stress in the near-wall region due to the presence of shear. Furthermore, we find that misalignment in the wire orientation cannot be fully accounted for through the calibration procedure, presumably due to increased sensitivity to an out-of-plane velocity component. This has strong implications if using a generic commercial cross-wire probe, since inclining these probes to gain access to the near-wall region can lead to a large error (up to 10 %) in turbulent stresses and these errors can manifest in the log region and beyond to half the boundary layer thickness. For uncertainties introduced during the calibration procedure, the Reynolds shear stress is observed to exhibit an elevated sensitivity compared with other turbulent stresses. This is consistent with empirical observations where the repeatability in the Reynolds shear stress is found to be the poorest.

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Hot Wire in Wall Proximity

Cited by 12 publications

References 6 publications

Turbulent Boundary Layer over a Piezoelectrically Excited Traveling Wave Surface

Turbulent Boundary Layer over a Piezoelectrically Excited Traveling Wave Surface

The physics of heat transfer from hot wires in the proximity of walls of different materials

Sensitivity of turbulent stresses in boundary layers to cross-wire probe uncertainties in the geometry and calibration procedure

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