Development of a Simple Compact Photodiode Array for Use with Linear Array-FLDI

Davenport, Kirk; Ledbetter, Shelby Y.; Siddiqui, Farhan; Gragston, Mark

doi:10.2514/6.2023-1563

Cited by 2 publications

(1 citation statement)

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“…The single-point FLDI employed in previous HDT experiments [23], which utilizes a Novanta Photonics Ventus solid state (𝜆 0 = 671𝑛𝑚) laser, is split into a 3x3 (9-point) grid with a diffractive optic element from HOLO/OR, as first suggested by Gragston et al [33]. The nine signals are recorded using a custom photodiode array inspired by, and very similar to the array described by Davenport et al [34]. The signals are recorded at 10𝑀 𝐻𝑧 by two separate Pico Technology picoscopes (4444 and 4284).…”

Section: Facility Model and Instrumentationmentioning

confidence: 99%

Experimental investigation of boundary layer instabilities and transition on sharp and blunt cones in Oxford’s High-Density Tunnel

Ceruzzi,

Le Page,

Kerth

et al. 2024

AIAA SCITECH 2024 Forum

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Boundary layer instabilities and transition to turbulence on a 7-degree half-angle cone with varying nose-tip radii in Mach 6 and 7 flow are investigated using a combination of surface heat transfer measurements, surface pressure measurements, and high speed schlieren images. The experiments are performed at unit-Reynolds numbers ranging from [22 − 44] × 10 6 /m in University of Oxford's High-Density Tunnel (HDT). The transition Reynolds number, 𝑅𝑒 𝑋 𝑇 , increases with increasing nose tip Reynolds number, 𝑅𝑒 𝑅 𝑁 , for 𝑅𝑒 𝑅 𝑁 ≤ 10 5 . In this range, evidence of second-mode wave instabilities are observed in both schlieren images and surface pressure measurements. For 10 5 < 𝑅𝑒 𝑅 𝑁 < 4 × 10 5 , 𝑅𝑒 𝑋 𝑇 remains constant and coherent streaks above the boundary layer are observed with schlieren imaging. Images of the interaction of these features with a boundary layer breaking down to a fully turbulent state are presented. The freestream disturbance environment is also varied through existence of several steady state plateaus created by the natural operation of the facility, and characterised with multi-point focused laser differential interferometry (FLDI). 𝑅𝑒 𝑋 𝑇 increases by ∼ 10 − 60% with increasing plateau number which is independent of 𝑅𝑒 𝑅 𝑁 . Variation in freestream fluctuation amplitude with frequency and Reynolds number are in agreement with previous studies while variation with plateau is not. The discrepancy is explained by receptivity functions which are sensitive to the inclination angle of disturbances. A method for measuring the inclination angle using correlated FLDI signals is presented and reveals a consistent trend with plateau number. The trend is physically explained by changes in the relative contribution of entropic and acoustic modes with time.

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Section: Facility Model and Instrumentationmentioning

confidence: 99%