Panda J.,NASA |
Schery S.D.,Aerospace Computing Inc.
AIAA AVIATION 2014 - 30th AIAA Aerodynamic Measurement Technology and Ground Testing Conference | Year: 2014
A Rayleigh scattering based density-fluctuations measurement system has been setup inside a low-speed wind tunnel of NASA Ames Research Center. The immediate goal of the test has been to study transition on a heated flat plate. At first a smaller scale setup was created around a small low-speed heated jet, and then the setup was modified for use in a wind tunnel. The paper discusses means of overcoming various difficulties associated with particle cleaning, vibration isolation and stray light reduction to obtain a cleaner signature of the Rayleigh scattered light. A two-PMT cross-correlation system and photo-electron counting processes were used to minimize the shot noise floor in the spectra of turbulent density fluctuations. Preliminary results from both setups are presented. It was found that a signal-to-noise ratio of 102 to 104 was achievable with increasing plume/plate temperature. Source
Hollis B.R.,NASA |
Hollingsworth K.E.,Aerospace Computing Inc.
42nd AIAA Fluid Dynamics Conference and Exhibit 2012 | Year: 2012
The boundary-layer transition characteristics and convective aeroheating levels on mid lift-to-drag ratio entry vehicle configurations have been studied through wind tunnel testing. Several configurations were investigated, including elliptically-blunted cylinders with both circular and elliptically-flattened cross sections, biconic geometries based on launch vehicle dual-use shrouds, and parametrically-optimized analytic geometries. Vehicles of this class have been proposed for high-mass Mars missions, such as sample return and crewed exploration, for which the conventional sphere-cone entry-vehicle geometries of previous Mars missions are insufficient. Testing was conducted at Mach 6 over a range of Reynolds numbers sufficient to generate laminar, transitional, and turbulent flow. Transition onset locations - both straight-line and cross-flow - and heating rates were obtained through global phosphor thermography. Supporting computations were performed to obtain heating rates for comparison with the data. Laminar data and predictions agreed to well within the experimental uncertainty. Fully-turbulent data and predictions also agreed well. However, in transitional flow regions, greater differences were observed. Additional aerodynamic performance data were also generated through Modified-Newtonian analyses of the geometries. Source
Almog N.,Aerospace Computing Inc. |
2013 Aviation Technology, Integration, and Operations Conference | Year: 2013
Preferential Merging is a best-equipped best-served air traffic management concept meant to accelerate the adoption of Automatic Dependent Surveillance-Broadcast Out (ADS-B Out) in the national airspace by giving an operational incentive to airlines who invest in upgrading their fleet. The concept relies on re-sequencing aircraft arrival order at en-route arrival merge-fixes favoring high-equipped aircraft (such as ADS-B Out) over low-equipped aircraft. This in turn reduces flight-time for high-equipped aircraft and moves them ahead in the arrival queue. In this study Preferential Merging was simulated using historical flight traffic into Phoenix Sky Harbor International Airport, focusing on a benefit analysis from an airline's perspective. A second set of Monte Carlo simulations randomizing aircraft equipage were run to determine the effectiveness of Preferential Merging as the percent of ADS-B Out equipped Aircraft increases. Results show that the policy creates a 4.5 minute reduction in total flight time for aircraft equipped with ADS-B Out, and that the incentive provided by the policy remains effective over a broad range of ratios of high- to low-equipage aircraft in the US airspace. Source
Panda J.,NASA |
Mosher R.,Aerospace Computing Inc.
49th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2011
A 70-element microphone phased array was used to identify noise sources in the plume of a solid rocket motor. A weather-resistant case was built and other precautions were taken to protect the sensitive condenser microphones from rain, thunderstorms and other environmental elements during prolonged stay in the outdoor test stand. A camera mounted at the center of the array was used to photograph the plume. In the first phase of the study the array was placed in an anechoic chamber for calibration and validation of the indigenous Matlab® based beamform software. It was found that the "advanced" beamform methods, such as CLEAN-SC were partially successful in indentifying speaker sources placed closer than the Rayleigh criterion. To participate in the field test, all of the equipment was shipped to NASA Marshal Space Flight Center, where the array hardware was rebuilt around the test stand. The sensitive amplifiers and the data acquisition hardware were placed in a safe basement, and 50m long cables were used to connect the microphones, Kulites and the camera. The array case and the microphones were found to withstand the environmental elements as well as the shaking from the rocket plume generated noise. The beamform map was superimposed on a photo of the rocket plume to readily identify the source distribution. It was found that the plume made an exceptionally long, greater than 30 diameter, noise source over a large frequency range. The shock pattern created spatial modulation of the noise source. Interestingly, the concrete pad of the horizontal test stand was found to be a good acoustic reflector: the beamform map showed two distinct source distributions- the plume and its reflection on the pad. The array was found to be most effective in the frequency range of 2 kHz to 10 kHz. As expected, the classical beamform method excessively smeared the noise sources at lower frequencies and produced excessive side-lobes at higher frequencies. The "advanced" beamform routine CLEAN-SC created a series of lumped sources which may be unphysical. We believe that the present effort is the first-ever attempt to directly measure noise source distribution in a rocket plume. Source
Panda J.,NASA |
Mosher R.,Aerospace Computing Inc.
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2012
A microphone phased array was used in the Ares I Scale Model Acoustics Test (ASMAT) to identify noise sources during the launch of the Ares I vehicle. Although the Ares I program has been discontinued, understanding gained from ASMAT is expected to benefit future launch vehicles. A 5%-scale model of the launch pad, the launch tower, and the Ares I vehicle was used in this test. A solid rocket motor was used to simulate the first stage booster. A 70-microphone array, suitably modified for high-noise, outdoor, all-weather application (Panda & Mosher 2011) was mounted on a tower in the vicinity of the model. Data acquired during the steady-part of the motor firing were analyzed using beamforming routines to identify the distribution of sources over the pad. Data were collected from many different configurations representing various stages of lift-off, such as: (a) model at hold-down position; (b) model at different elevations with the accompanying lateral drift; (c) absence or presence of various water injection systems; and (d) absence or presence of a Launch Mount. The beamformed plots show that, in almost all cases, impingement by the plume on various regions of the pad constitutes the primary noise sources. The scenario is very different from the current models and expectations based on NASA SP-8072 (Eldred & Jones 1971) and its variations, which assumes the plume itself as the noise source and does not take into account the importance of impingement. It was found that another parameter, the sidewise drift of the vehicle with elevation, influenced the strength of the impingement noise sources, yet was not considered in the prediction methods. It was observed that the addition of water in the trench and in the hole of the Mobile Launch Platform (MLP) attenuated noise sources radiating from these places. Water injection on the top of the MLP, so-called "rainbird" system, produced some relief but the impingement source remained active. The noise source maps suggest that the minimization of plume impingement by minimizing the vehicle drift in the early part of liftoff, covering-up the trench as much as possible, and by removing extraneous components such as the Launch Mount will lead to a reduction of the liftoff acoustics level. Source