Measurements of Turbulence in a Subsonic Air Jet

Laurence, J. C.

doi:10.1121/1.1905102

Cited by 4 publications

(4 citation statements)

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“…This shows that the tripping successfully provokes transition to turbulence, leading to a canonical boundary layer upstream of the nozzle exit. Peak turbulence intensity levels on the shear layer just downstream of the exit plane, where control is applied, were found to be between 12% and 15%, which is typical for jets issuing from nozzles with turbulent boundary layers [92][93][94][95][96][97].…”

Section: Methodsmentioning

confidence: 92%

Real-time reactive control of stochastic disturbances in forced turbulent jets

et al. 2021

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In this work we perform reactive control of stochastic disturbances in forced turbulent jets based on destructive interference. The study is motivated by the success of recent studies in applying this type of control on instability waves in transitional boundary layers and free-shear flows. Linear convective mechanisms in the initial region of turbulent jets are explored in order to perform reactive control, wherein the actuation signal is updated in real time based on sensor measurements performed upstream, resulting in an inverse feedforward approach. The control law is based on empirical transfer functions of the jet response to stochastic forcing and actuation, which are measured experimentally. Since turbulent jets have energy content spread in a number of azimuthal wavenumbers, we apply axisymmetric forcing at the nozzle lip in order to be able to perform control using a reduced number of sensors and actuators. The external forcing produces axisymmetric wavepackets which possess stochastic phases and amplitudes, akin to turbulent fluctuations found in unforced jets. We demonstrate the successful implementation of real-time reactive control of these disturbances, achieving order-of-magnitude attenuations of associated velocity fluctuations. Control is shown to reduce fluctuation levels over an extensive streamwise range.

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Section: Methodsmentioning

confidence: 92%

Real-time reactive control of stochastic disturbances in forced turbulent jets

et al. 2021

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“…The AeroAcoustic Propulsion Laboratory (AAPL), the location at NASA GRC selected for this series of tests, possesses, by its very nature, a number of features that could hinder or completely preclude the performance of certain optical diagnostics. Several major considerations include: (1) the AAPL is open to the outside environment and as such experiences large temperature variations over the course of a day-long test; (2) high sonic noise levels upwards of 115 dB;…”

Section: Project Descriptionmentioning

confidence: 99%

“…Since the first reported measurement by Laurence [1] in 1954, researchers have been studying high velocity turbulent jets in order to better understand the fluid dynamics of these flows. Even after all the years of study, much is left unknown primarily due to the difficulties encountered when trying to measure flow parameters, particularly temperature, in heated jets from subsonic to supersonic velocities.…”

Section: Introductionmentioning

confidence: 99%

Rotational Raman-based temperature measurements in a high-velocity, turbulent jet

Locke¹,

Wernet

Anderson

2017

Meas. Sci. Technol.

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Spontaneous rotational Raman scattering spectroscopy is used to acquire measurements of the mean and root mean square (rms) temperature fluctuations in turbulent, high-velocity heated jets. Raman spectra in air were obtained across a matrix of radial and axial locations downstream from a 50 mm diameter nozzle operating from subsonic to supersonic conditions over a wide range of temperatures and Mach numbers, in accordance with the Tanna matrix frequently used in jet noise studies. These data were acquired in the hostile, high noise (115 dB) environment of a large scale open air test facility at NASA Glenn Research Center (GRC). Temperature estimates were determined by performing non-linear least squares fitting of the single shot spectra to the theoretical rotational Stokes spectra of N2 and O2. The laser employed in this study was a high energy, long-pulsed, frequency doubled Nd:YAG laser. One thousand single-shot spectra were acquired at each spatial coordinate. Mean temperature and rms temperature variations were calculated at each measurement location. Excellent agreement between the averaged and single-shot temperatures was observed with an accuracy better than 2.5% for temperature, and rms variations in temperature between ±2.2% at 296 K and ±4.5% at 850 K. The mean and normalized rms temperatures measured here were then compared to NASA’s Consensus data set of PIV velocity and turbulence measurements in similar jet flows. The results of this and planned follow-on studies will support NASA GRC’s development of physics-based jet noise prediction, turbulence modeling and aeroacoustic source modeling codes.

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“…There is a large collection of flow statistics data on cold jets, where space-time correlations have been performed to estimate turbulent length and time scales [5,6]. However, cold jet flow data are not directly applicable to hot jet flows.…”

Section: Introductionmentioning

confidence: 99%

Temporally resolved PIV for space–time correlations in both cold and hot jet flows

Wernet¹

2007

Meas. Sci. Technol.

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Temporally resolved particle image velocimetry (TR-PIV) is the newest and most exciting tool recently developed to support our continuing efforts to characterize and improve our understanding of the decay of turbulence in jet flows—a critical element for understanding the acoustic properties of the flow. A new TR-PIV system has been developed at the NASA Glenn Research Center which is capable of acquiring planar PIV image frame pairs at up to 25 kHz. The data reported here were collected at Mach numbers of 0.5 and 0.9 and at temperature ratios of 0.89 and 1.76. The field of view of the TR-PIV system covered six nozzle diameters along the lip line of the 50.8 mm diameter jet. The cold flow data at Mach 0.5 were compared with hotwire anemometry measurements in order to validate the new TR-PIV technique. The axial turbulence profiles measured across the shear layer using TR-PIV were thinner than those measured using hotwire anemometry and remained centred along the nozzle lip line. The collected TR-PIV data illustrate the differences in the single point statistical flow properties of cold and hot jet flows. The planar, time-resolved velocity records were then used to compute two-point space–time correlations of the flow at the Mach 0.9 flow condition. The TR-PIV results show that there are differences in the convective velocity and growth rate of the turbulent structures between cold and hot flows at the same Mach number.

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Measurements of Turbulence in a Subsonic Air Jet

Cited by 4 publications

References 0 publications

Real-time reactive control of stochastic disturbances in forced turbulent jets

Real-time reactive control of stochastic disturbances in forced turbulent jets

Rotational Raman-based temperature measurements in a high-velocity, turbulent jet

Temporally resolved PIV for space–time correlations in both cold and hot jet flows

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