On the directional sensitivity of hot-wires: a new look at an old phenomenon

Wagner, Terrance C.; Kent, J. C.

doi:10.1007/bf00196602

Cited by 11 publications

(6 citation statements)

References 8 publications

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“…This contribution was shown to be dependent on the sensor geometry. 16 As shown in Fig. 6, both the mean and RMS values for T ave /(b/U 0 ) = 660 agree with those for T ave /(b/U 0 ) = 1100.…”

Section: E Initial Flow Fieldsupporting

confidence: 83%

Flows around a cascade of flat plates with acoustic resonance

Yokoyama¹,

Kitamiya²,

Iida³

2013

Physics of Fluids

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In order to better understand the effects of acoustic resonance on flows around a cascade of flat plates, fluid structures and acoustic fields were examined by aeroacoustic direct simulations and wind tunnel experiments. Computations and experiments were performed for the flows around five parallel plates with and without the acoustic resonance changing the freestream velocity. The aspect ratio of the plates, C/b, is 15.0, and the separation-to-thickness ratio, s/b, is 6.0. For the resonant condition of a freestream velocity of 44 m/s, the Reynolds number based on the plate thickness, b, and the freestream velocity is 5.8 × 103. The computational results revealed that large-scale vortices composed of fine-scale vortices are shed in the wake of the plates. Both experimental and computational results indicated that the shedding of the large-scale vortices is more synchronized in the spanwise direction for the resonant condition. Moreover, the shedding of the large-scale vortices from one plate and those from the neighboring plates become more synchronized in the resonant condition. The mode of this synchronization was found to be an anti-phase mode, in which the vortex is shed from the upper or lower face of one plate when the vortex is shed from the lower or upper faces of the neighboring plates. Computation of the flow around a single plate was also performed, and the radiation of the acoustic waves from the downstream edge due to vortex shedding from the plate was indicated. When acoustic resonance occurs in the flows around the cascade of flat plates, vortex shedding in the above-mentioned mode contributes to the intensification of the standing waves between the plates. Moreover, standing waves were demonstrated to induce new vortices around the upstream edges of the plates in synchronization.

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Section: E Initial Flow Fieldsupporting

confidence: 83%

Flows around a cascade of flat plates with acoustic resonance

Yokoyama¹,

Kitamiya²,

Iida³

2013

Physics of Fluids

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“…More information on the directional sensitivity of hot wires can be found in Refs. [26][27][28]. While 10 to 20 degrees of error in the angle results in less than 2% error in the velocity measurement, the error can go up to 15% for larger angles.…”

Section: B Hot-wire Anemometermentioning

confidence: 99%

Sweeping Jet Actuator in a Quiescent Environment

Köklü

Melton

2013

43rd Fluid Dynamics Conference

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This study presents a detailed analysis of a sweeping jet (fluidic oscillator) actuator. The sweeping jet actuator promises to be a viable flow control actuator candidate due to its simple, no moving part structure and its high momentum, spatially oscillating flow output. Hot-wire anemometer and particle image velocimetry measurements were carried out with an emphasis on understanding the actuator flow field in a quiescent environment. The time averaged, fluctuating, and instantaneous velocity measurements are provided. A modified actuator concept that incorporates high-speed solenoid valves to control the frequency of oscillation enabled phase averaged measurements of the oscillating jet. These measurements reveal that in a given oscillation cycle, the oscillating jet spends more time on each of the Coanda surfaces. In addition, the modified actuator generates four different types of flow fields, namely: a non oscillating downward jet, a non oscillating upward jet, a non oscillating straight jet, and an oscillating jet. The switching from an upward jet to a downward jet is accomplished by providing a single pulse from the solenoid valve. Once the flow is switched, the flow stays there until another pulse is received. The oscillating jet is compared with a non oscillating straight jet, which is a typical planar turbulent jet. The results indicate that the oscillating jet has a higher (5 times) spreading rate, more flow entrainment, and higher velocity fluctuations (equal to the mean velocity). Nomenclature = flow angle, degree K 2 = pitch factor U = velocity magnitude, m/s Ueff = effective cooling velocity, m/s Umax = local maximum velocity, m/s x = streamwise location, mm z = spanwise location, mm Abbreviations: HWA = hot-wire anemometer PIV = particle image velocimetry RMS = root mean square SWJ = sweeping jet VGJ = vortex generator jet Subscripts: ° = angle, degree ` = root mean square of fluctuating value

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“…The effective cooling velocity, U eff (φ) of a flow with free stream velocity, U ∞ and at yaw angle φ relative to the gauge is composed of the normal component of velocity, U ∞ cos φ and some contribution from the axial velocity component U ∞ sin φ: where k 2 1 is the yaw factor. The usefulness of equation ( 1) has been confirmed by many experimentalists [1][2][3][4][5][6][7] for hotwire gauges where k 2 1 is typically a small positive number less than 0.1 [1][2][3][4][5][6][7], but may also be negative [4]. It follows from (1) that…”

Section: Background Theorymentioning

confidence: 92%

Directional sensitivity of wall mounted hot-film gauges

Elvery

Bremhorst

1996

Meas. Sci. Technol.

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The directional sensitivity of a constant temperature, thin, wall mounted hot-film gauge with respect to variations in yaw angle is investigated. Results obtained for the response of a hot-film gauge in a boundary layer flow fit the correlation between the effective cooling velocity for a hot-wire gauge and the yaw angle suggested by other workers. The yaw factor used in this correlation is typically less than 1.0. Results presented for the hot-film gauge in a boundary layer indicate that the yaw factor depends on both the distance into the boundary layer and the magnitude of the free stream velocity. At some velocity, close to zero, the results predict a yaw factor greater than unity. Computer simulations using the turbulence model are presented which verify this prediction. Yaw factors greater than one result because diffusion from the edges of the gauge becomes significant at low velocities with respect to the total heat transferred.

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On the directional sensitivity of hot-wires: a new look at an old phenomenon

Cited by 11 publications

References 8 publications

Flows around a cascade of flat plates with acoustic resonance

Flows around a cascade of flat plates with acoustic resonance

Sweeping Jet Actuator in a Quiescent Environment

Directional sensitivity of wall mounted hot-film gauges

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