The capabilities and limitations of angular scatterometry for a structure pitch much less than the optical wavelength are experimentally investigated using a 100-nm pitch Al-wire grid polarizer on a SiO2 substrate. Three CW laser sources of wavelengths (244 nm, 405 nm and 633 nm) are used to measure the 0-order diffraction (reflection) across an incident angle range of 8 degrees to 80 degrees. The grating profile is defined by seven parameters (pitch, bottom linewidth, top linewidth, fused silica undercut, Al thickness, horizontal and vertical extent of top rounding). Rigorous coupled wave analysis (RCWA) simulations show that the reflectivity versus angle results are sensitive to changes in all of these parameters. The simulations act as a baseline library for the scatterometry measurements. Fitting the experimental curves with the corresponding simulation parameters results in a determination of the grating profile. As expected the shorter wavelength measurements provide the most sensitivity, but good precision is obtained at all three wavelengths. The measurements are in good agreement with destructive cross section scanning electron microscopy measurements.
Although EOR with CO2 is practiced domestically on large scale, the potential for advancement is enormous. The ongoing search for better solutions has motivated extensive research on alternatives to surfactant-stabilized CO2 foams for CO2 mobility control. The formation of CO2-in-water foams lowers the CO2 mobility, resulting in improvement in sweep efficiency in field tests. The crucial unmet challenge in employing CO2 foams is to maintain long-term stability of foam to achieve high sweep efficiency for the duration of the flooding process. Surfactant-stabilized foams are inherently unstable so that maintenance of the low mobility requires continuous regeneration of lamellae in the small pores of the rock. Nanoparticles can potentially be used to provide much higher foam stability and thus long-term mobility control for CO2 floods. They can act like a foaming surfactant without some of the surfactant drawbacks. Here we present a turnkey approach for using surface treated nanoparticles in reservoirs. This involves: tests for stability in brines, transportability through cores, foam generation in beadpacks and cores when co-injected with CO2, quantification of CO2 viscosity enhancement, and finally modeling of field-scale effects. In this paper, we will outline the key details of nanoparticle design for CO2 EOR.
High area ratio rockets generate strong vibro-acoustic loads primarily during transient operations, like start-up and shut-down of the engine. These loads can adversely affect the launch vehicle and its payload. Thus, an accurate prediction of the loads produced during engine start-up is pertinent to the safety and reliability of the launch vehicle. The present work focuses on developing a robust framework for predicting these loads using laboratory scale rocket nozzles tested in the fully anechoic chamber at The University of Texas at Austin. This encompasses corrections for the observer position relative to the prominent source region, as well as scaling factors to correct for geometric factors. The test campaign encompasses single, two, three and four nozzle clusters, as well as differences in nozzle geometry and operating conditions (nozzle pressure ratio).
The plume produced by a cluster of two high area-ratio thrust optimized parabolic contour nozzles is visualized by way of retroreflective shadowgraphy. Both steady and transient operations of the nozzles (start-up and shut-down) were conducted in the anechoic chamber and high speed flow facility at The University of Texas at Austin. Both nozzles exhibit free shock separated flow, restricted shock separated flow and an end-effects regime prior to flowing full. Radon transforms of the shadowgraphy images are used to identify the locations in the flow where sound waves are being generated. During these off design operations of the nozzles, most sound waves are generated by turbulence interactions with the shock cells located in the supersonic annular plume. During the end-effects regime, this supersonic annular plume is shown to flap violently, thus providing a first principals understanding of the sources of most intense loads during engine ignition.
C. E. Tinney, Canchero, A., Rojo, R., Mack, G., Murray, N. E., and Ruf, J. H., “The Sound-field Produced by Clustered Rockets During Startup,” Whither Turbulence and Dig Data for the 21st Century. Symposium held at the Institute dEtudes Scientifques de Cargese, Corsica, France, April 20-24, (Springer Hardbound Volume, DOI: 10.1007/978-3-319-41217-7), 2015.Abstract
The vibroacoustic loads produced by a cluster of two large area-ratio thrust optimized parabolic contour nozzles are studied over a range of pressure ratios encompassing free-shock separated flow, restricted shock separated flow and the end-effects-regime. The rocket plume is visualized using a retroreflective shadowgraphy system while an experimentally validated RANS model provides insight into the internal flow and shock structure patterns. Pressure loads that form on the base of the vehicle (behind the nozzles) are then measured using a eighth-inch microphone, as most of these loads are caused by high intensity sound waves produced by the rocket nozzle flow. The objective of the study is to provide a direct link between the sources of most intense vibro-acoustic loads that form during the ignition of high area ratio rocket nozzle clusters.