Engineering topics

D M Nark

Publications and source records attributed to D M Nark.

3 records

NASA NTRS2024

Examination of Perforate Facesheet Impedance Prediction Models

This study examines several perforate facesheet impedance prediction models. Each model is validated with impedances educed from acoustic pressure measurements acquired in the NASA Langley Research Center Normal Incidence Tube (NIT) and Grazing Flow Impedance Tube (GFIT). This measurement dataset includes results for 73 NIT samples acquired at sound pressure levels of 100, 120, and 140 dB, and for 9 GFIT samples acquired at SPLs of 120 and 140 dB and at mean flow speeds of Mach 0.0, 0.3, and 0.5. Multiple metrics are evaluated based on different potential applications of the selected perforate facesheet model. An optimizer is then used to modify one of these models to more accurately match the full measurement dataset.

acoustic↗

NASA NTRSDate not supplied

Evaluation of Variable-Depth Liners with Slotted Cores

An initial evaluation of variable-depth, slotted-core liners fabricated with conventional, flightworthy com-ponents is presented. Liners with two distinct chamber lengths provide significant broadband absorption and their impedances are, to first order, predictable with the NASA impedance prediction code. These liners employ film caps embedded in alternating chambers to provide a near-rigid boundary condition. This enables improved control of the liner design process. A number of additively-manufactured, bent-chamber liners are also investigated to explore the e˙ects of the bend on the liner impedance. The liner impedance is negligibly a˙ected by changes to the partition width, but is significantly a˙ected by changes to the slot height. This o˙ers an option for achieving low-frequency sound absorption with relatively thin liners.

acoustic↗

NASA NTRSDate not supplied

NASA Investigation of Flow Direction Effects on Impedance Eduction for Acoustic Liners

In support of a collaboration with the International Forum for Aviation Research (IFAR), the NASA Langley Liner Physics Team has acquired a detailed dataset for use in the evaluation of flow direction effects on the acoustic liner impedance eduction process. Measurements are acquired with four acoustic liners designed to cover a range of sensitivities to source sound pressure level and tangential mean flow effects, specifically at source levels of 120 and 140 dB and centerline Mach numbers of 0.0, 0.1, 0.2, and 0.3. These measurements include detailed flow profile surveys upstream and downstream of the liner test window, as well as acoustic pressure data over the extent of the test window. The results clearly demonstrate the importance of the choice of Mach number used in the impedance eduction analysis. Average Mach number differences of less than 0.01 result in significant variation in the educed impedance spectra. These data will soon be supplied to the IFAR partners and will be made available for the general public within the next year.

acoustic↗