skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Attention:

The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Friday, July 11 until 2:00 AM ET on Saturday, July 12 due to maintenance. We apologize for the inconvenience.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Development and Calibration of a new Anechoic Wall Jet Wind Tunnel
A new Anechoic Wall Jet Wind Tunnel was built at Virginia Tech. A detailed design based on the old wall jet tunnel was done to improve the quality of the resultant flow. Aerodynamic and acoustic calibrations were performed in order to understand properties and characteristics of the flow generated by this new facility which can be used for various aeroacoustic studies. Far-field acoustics were measured using half-inch B&K microphones in a streamwise array to characterize and reduce the background noise. Sound pressure levels were lower by 10 dB for frequencies up to 700Hz in comparison to the old facility. The turbulent surface pressure fluctuations of the wall-jet flow were studied using Sennheiser microphones placed along streamwise and spanwise locations to record surface pressure fluctuations. Comparison of the autocorrelation plotted for microphones along the same span indicate uniform flow features. A decay in the turbulence levels is observed along the downstream direction as expected. Aerodynamic calibrations included mean velocity measurements along different spanwise locations, wall-jet boundary layer profiles and streamwise cross-sections. Spanwise and cross-sectional velocity profiles show good uniformity of the flow. Detailed boundary layer analyses were performed with the parameters obtained from the experiments.  more » « less
Award ID(s):
1802915
PAR ID:
10093468
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Date Published:
Journal Name:
AIAA Science and Technology Forum and Exposition 2019
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, Journal of Fluids Engineering)
    null (Ed.)
    Abstract Coherent structures are critical for controlling turbulent boundary layers due to their roles in momentum and heat transfer in the flow. Turbulent coherent structures can be detected by measuring wall shear stresses that are footprints of coherent structures. In this study, wall shear stress fluctuations were measured simultaneously in a zero pressure gradient turbulent boundary layer using two house-made wall shear stress probes aligned in the spanwise direction. The wall shear stress probe consisted of two hot-wires on the wall aligned in a V-shaped configuration for measuring streamwise and spanwise shear stresses, and their performance was validated in comparison with a direct numerical simulation result. Relationships between measured wall shear stress fluctuations and streamwise velocity fluctuations were analyzed using conditional sampling techniques. The peak detection method and the variable-interval time-averaging (VITA) method showed that quasi-streamwise vortices were inclined toward the streamwise direction. When events were simultaneously detected by the two probes, stronger fluctuations in streamwise velocity were detected, which suggests that stronger coherent structures were detected. In contrast to the former two methods, the hibernating event detection method detects events with lower wall shear stress fluctuations. The ensemble-averaged mean velocity profile of hibernating events was shifted upward compared to the law of the wall, which suggests low drag status of the coherent structures related with hibernating events. These methods suggest significant correlations between wall shear stress fluctuations and coherent structures, which could motivate flow control strategies to fully exploit these correlations. 
    more » « less
  2. ; ; ; ; ; (, AIAA Scitech 2019 Forum)
    Direct numerical simulations (DNS) of the full-scale axisymmetric nozzle of a Mach 8 wind tunnel are conducted with an emphasis on characterizing the properties of the pressure fluctua- tions induced by the turbulent boundary layer (TBL) along the nozzle wall. The axisymmetric nozzle geometry and the flow conditions of the DNS match those of the Sandia Hypersonic Wind Tunnel at Mach 8. The mean and turbulence statistics of the nozzle-wall boundary layer show good agreement with those predicted by Pate’s correlation and Reynolds Averaged Navier-Stokes (RANS) computations. The wall-pressure intensity, power spectral density, and coherence predicted by DNS show good comparisons with those measured in the same tunnel. The Corcos model is found to deliver good prediction of wall pressure coherence over inter- mediate and high frequencies. The streamwise and spanwise decay constants at Mach 8 are similar to those predicted by DNS and experiments at lower supersonic Mach numbers. 
    more » « less
  3. ; (, Journal of Fluid Mechanics)
    This paper employs an input–output based approach to analyse the convective velocities and transport of fluctuations in turbulent channel flows. The convective velocity for a fluctuating quantity associated with streamwise–spanwise wavelength pairs at each wall-normal location is obtained through the maximization of the power spectral density associated with the linearized Navier–Stokes equations with a turbulent mean profile and delta-correlated Gaussian forcing. We first demonstrate that the mean convective velocities computed in this manner agree well with those reported previously in the literature. We then exploit the analytical framework to probe the underlying mechanisms contributing to the local convective velocity at different wall-normal locations by isolating the contributions of each streamwise–spanwise wavelength pair (flow scale). The resulting analysis suggests that the behaviour of the convective velocity in the near-wall region is influenced by large-scale structures further away from the wall. These structures resemble Townsend’s attached eddies in the cross-plane, yet show incomplete similarity in the streamwise direction. We then investigate the role of each linear term in the momentum equation to isolate the contribution of the pressure, mean shear, and viscous effects to the deviation of the convective velocity from the mean at each flow scale. Our analysis highlights the role of the viscous effects, particularly in regards to large channel spanning structures whose influence extends to the near-wall region. The results of this work suggest the promise of an input–output approach for analysing convective velocity across a range of flow scales using only the mean velocity profile. 
    more » « less
  4. (, AIAA Aviation 2021)
    null (Ed.)
    An analytical approach has been developed to model the rapid term contribution to the unsteady surface pressure fluctuations in wall jet turbulent boundary layer flows. The formulation is based on solving Poisson’s equation for the turbulent wall pressure by integrating the source terms (Kraichnan, 1956). The inputs for the model are obtained from 2D time-resolved Particle Image Velocimetry measurements performed in a wall jet flow. The wall normal turbulence wavenumber two-point cross-spectra is determined using an extension of the von Kármán homogeneous turbulence spectrum. The model is applied to compare and understand the baseline flow in the wall jet and to study the attenuation in surface pressure fluctuations by unidirectional canopies (Gonzales et al, 2019). Different lengthscale formulations are tested and we observe that the wall jet flow boundary layer contributes to the surface pressure fluctuations from two distinct regions. The high frequency spectrum is captured well. However, the low frequency range of the spectrum is not entirely captured. This is because we have used PIV data only up to a height of 2.3𝜹, whereas the largest turbulent lengthscales in the wall jet are on the order of 𝒚𝟏/𝟐≈𝟔𝜹. Using the flow data obtained from PIV and Pitot probe measurements, the model predicts a reduction in the surface pressure due to canopy at low frequencies. 
    more » « less
  5. ; ; ; ; ; (, 20th International Symposium on Application of Laser and Imaging Techniques to Fluid Mechanics)
    The fluid-structure interaction (FSI) of a compliant panel under a compression-ramp-induced shock/boundary-layer interaction (SBLI) has been studied in Mach 2 flow. Simultaneous high-speed measurements of the velocity field and the panel displacement were conducted using 50 kHz particle image velocimetry (PIV) and 5 kHz stereoscopic digital image correlation (DIC). The mean effect of the panel displacement has been evaluated by monitoring the change in velocity profiles along the streamwise direction (x), upstream of the separated flow region. Streamwise (u) velocity near the panel surface has been shown to change its magnitude in response to the wall shape. Furthermore, the strong cross-correlation between fluctuations of the wall-normal panel displacement and the transverse (v) velocity can be explained by the flow remaining tangent to the wall surface as the panel deforms. This latter result is consistent with the panel motion being sufficiently low frequency compared to flow convective time scales that the flow is quasi-steady In addition, assessment of the correlation between the separation shock position and panel displacement seems to suggest that when the panel is bulged down (concave up) at the downstream end of the panel, a larger separated flow is generated and the shock moves upstream. This observation remains speculative, but is consistent with the flow undergoing greater compression for the bulged down case. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email