Numerical Simulations of Instabilities in Single-Hole Office Elements

An orifice element is commonly used in liquid rocket engine test facilities either as a flow metering device, a damper for acoustic resonance or to provide a large reduction in pressure over a very small distance in the piping system. While the orifice as a device is largely effective in stepping down pressure, it is also susceptible to a wake-vortex type instability that generates pressure fluctuations that propagate downstream and interact with other elements of the test facility resulting in structural vibrations. Furthermore in piping systems an unstable feedback loop can exist between the vortex shedding and acoustic perturbations from upstream components resulting in an amplification of the modes convecting downstream. Such was the case in several tests conducted at NASA as well as in the Ariane 5 strap-on P230 engine in a static firing test where pressure oscillations of 0.5% resulted in 5% thrust oscillations. Exacerbating the situation in cryogenic test facilities, is the possibility of the formation of vapor clouds when the pressure in the wake falls below the vapor pressure leading to a cavitation instability that has a lower frequency than the primary wake-vortex instability. The cavitation instability has the potential for high amplitude fluctuations that can cause catastrophic damage in the facility. In this paper high-fidelity multi-phase numerical simulations of an orifice element are used to characterize the different instabilities, understand the dominant instability mechanisms and identify the tonal content of the instabilities

Low-Cost Flow Visualization for a Supersonic Ejector

Shadowgraph techniques were applied to the cold flow ejector facility at the Propulsion Research Center at the University of Alabama in Huntsville. The setup for the experiments was relatively simple and was accomplished at very little cost. Series of shadowgraph images were taken of both dual nozzle and single nozzle strut based ejectors operating over a range of chamber pressures. The density gradient patterns in the shadowgraphs were compared to pressure data measured along the top and side walls of the mixing duct. The shadowgraph images showed the presence of barrel shocks emanating from the nozzles which at low pressures terminated in Mach disks and at higher pressures extended beyond the barrel shape and reflected off the walls of the duct. Based on pressure data from previous testing, reflected shocks were expected on the walls of the duct. The shadowgraph images confirmed the locations of these reflected shocks on the top wall of the duct. The shadowgraph images also showed the structure change which correlated to a change in pitch of the ejector noise, and corresponded to a change in trend of the duct wall pressure ratio distributions. The images produced from the setup provided insight into the complex flow behavior inside the ejector duct. In addition, the techniques were a valuable tool as an educational device for students

Uncertainty Analysis of Experimental Discharge Coefficients in Additively Manufactured Liquid Injector Elements

Screening of two additively manufactured liquid injector designs was conducted in the UAH high pressure spray facility. Four variants of each geometry with slightly different dimensions were obtained from eleven separate commercial additive manufacturing services. The devices were manufactured from Inconel 625 using the selective laser melting (SLM) powder bed process. The devices were cold flowed with water over a range of relevant pressure drops (75 psi to 1500 psi) to produce water flow rates from 0.037 to 1.75 lbm/s into ambient back pressure. Discharge coefficients determined from the testing along with the associated uncertainties provide insight into characteristic flow performance variabilities that can be expected from the SLM process for similar geometries

Uncertainty Analysis of Experimental Discharge Coefficients in Additively Manufactured Liquid Injector Elements

No abstract availabl

Late archaic settlement on the May River : data recovery at the Tree Runner Site (38BU1800), Beaufort County, South Carolina

Lying in a mature mixed pine and hardwood forest, the Tree Runner Site rests near the crest of the bluff overlooking a freshwater marsh of the May River. The site was recommended as potentially eligible for the National Register due to its potential to add significantly to our understanding of SC's Pre-Contact Period

Capsular contracture rate in a low-risk population after primary augmentation mammaplasty

BACKGROUND: The safety of augmentation mammaplasty has increased dramatically in the past 20 years. Capsular contracture (CC) is the most commonly reported complication of augmentation mammaplasty. OBJECTIVES: The authors report the incidence of CC in a low-risk patient population after primary augmentation. METHODS: The authors retrospectively reviewed the charts of 856 consecutive patients who underwent primary augmentation mammaplasty between 1999 and 2009. This series did not include patients who underwent breast augmentation-mastopexy, secondary augmentation, revision, and/or reconstruction. Data points included demographics, functional and aesthetic outcomes, complications, and revision rate/type. RESULTS: The overall incidence of CC in 856 patients was 2.8%. Average follow-up time was 14.9 months. Antibiotic irrigation decreased CC rates from 3.9% to 0.4% (P = .004). Tobacco users had higher rates of contracture than nonsmokers (5.5% vs 1.9%; P = .036). Saline implants had a higher CC rate than silicone gel (4.3% vs 1.3%; P = .032). Using multivariate logistic regression, CC was 7.89 times more likely in saline implants than in silicone gel (P = .027, 95% confidence interval, 1.26-49.00). CONCLUSIONS: Based on our findings, it is apparent that the early CC rate in primary augmentation can be less than 1%. To avoid CC, we advocate an inframmamary approach, submuscular implant placement, and antibiotic irrigation of the breast pocket. LEVEL OF EVIDENCE: 3