Optimization of a Mach-6 Quiet Wind-Tunnel Nozzle

Lakebrink, Matthew T.; Bowcutt, Kevin; Winfree, Troy; Huffman, Christopher C.; Juliano, Thomas J.

doi:10.2514/1.a33794

Cited by 19 publications

(2 citation statements)

References 21 publications

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“…For this run, the total temperature, T0, was recorded at 455.37K, the total pressure, P0, was recorded at 655kPa, and the back pressure, Pb, was recorded at 1.5kPa. More information on the specifications of the Mach 6 Quiet Tunnel can be found in Lakebrink et al 27 The lenslet array had a pitch of 0.0003m and a focal length of 0.0382m. Intensity-weighted slopes for both weighting functions are shown alongside the unweighted slopes in Fig.…”

Section: Resultsmentioning

confidence: 99%

Robust, regularized wavefront reconstruction of Shack-Hartmann data in discontinuous flow

Noel,

Kemnetz,

Gordeyev

et al. 2023

Unconventional Imaging, Sensing, and Adaptive Optics 2023

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Current Shack-Hartmann Wavefront Sensor (SHWFS) reconstruction algorithms for aero-optical research underperform in the presence of flow features with strong density gradients, such as shockwaves in supersonic flow. The large density variations in shockwaves violate the key underlying assumption of SHWFS; that local changes in the wavefront within the lenslet subaperture manifest primarily as tip/tilt. In these cases, the image-plane irradiance pattern of individual lenslets can exhibit high-order aberrations, resulting in non-tip/tilt behaviors. Standard least-squares wavefront reconstruction methods fail to accurately recover the wavefront in the presence of a shock due to the least-squares estimator’s tendency to give too much “influence” to outliers present in the measured SHWFS data, resulting in an underprediction of the optical-path difference (OPD) across the shock. A new algorithm is described to overcome the limitations of the standard least-squares reconstruction method. Two weighting functions are investigated with the aim of using additional intensity information to quantify the degree to which each subaperture is aberrated. The least-squares estimator is replaced with a robust estimator to perform outlier handling and regularizing terms are then used to further constrain the spatial organization of the solution. The problem of wavefront reconstruction is cast as a global functional optimization problem where minimization is achieved iteratively. The algorithm is then evaluated on a sample of Mach 6 SHWFS dot patterns where oblique shocks produce flow discontinuities. The results show that the algorithm is capable of accurately targeting discontinuous flow features as outliers, and subsequently altering those outliers, increasing the OPD as well as the sharpness of the shockwave structure.

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Section: Resultsmentioning

confidence: 99%

Robust, regularized wavefront reconstruction of Shack-Hartmann data in discontinuous flow

Noel,

Kemnetz,

Gordeyev

et al. 2023

Unconventional Imaging, Sensing, and Adaptive Optics 2023

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“…Mach 7 facilities are currently operational [29]. Other Ludwieg tubes recently constructed in academia include those developed by the University of Oxford [30], University of Notre Dame [31], University of Maryland [32], and the University of Arizona [33]. The Oxford High Density Tunnel (HDT) employs a fast-acting plug valve similar to that used in the AFRL wind tunnel and is designed for variable Mach numbers ranging from 3 to 7 with a 760 mm (29.92 in.)…”

Section: Introductionmentioning

confidence: 99%

Flow Characterization of the UTSA Hypersonic Ludwieg Tube

et al. 2023

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The characterization of a hypersonic impulse facility is performed using a variety of methods including Pitot probe scans, particle image velocimetry, and schlieren imaging to verify properties such as the velocity, Mach number, wall boundary layer thickness, and freestream turbulence intensity levels. The experimental results are compared to the numerical simulations of the facility performed with Ansys Fluent to compare the design and operational conditions. The presentation of results in this manuscript is prefaced by a description of the facility and its capabilities. The UTSA Ludwieg tube facility can produce a hypersonic freestream flow with a Mach number of 7.2 ± 0.2 and unit Reynolds numbers of up to 200 × 106 m−1. The Pitot probe profiles of the 203-mm-square test section indicate a 152 ± 10 mm square freestream core with turbulence intensity values ranging from 1% to 2%. Schlieren imaging of the oblique shockwaves on a 15° wedge model provided an alternate means of verifying the Mach number. Particle image velocimetry and previous molecular tagging velocimetry results showed a good agreement with the Pitot probe data and numerical simulations in the key parameters including freestream velocity, wall boundary layer velocity profiles, and wall boundary layer thickness.

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