Three-component laser anemometer measurement systems

A brief overview of the different laser anemometer (LA) optical designs available is presented. Then, the LA techniques that can be used to design a three-component measurement system for annular geometries are described. Some of the facility design considerations unique to these LA systems are also addressed. Following this, the facilities and the LA systems that were used to successfully measure the three components of velocity in the blading of annular-flow machines are reviewed. Finally, possible LA system enhancements and future research directions are presented

Aeroelastic study of the effect of the leakage flow in shrouded low-speed fans

A large-amplitude axial vibration of a rotor fan with shrouded blades has been experimentally observed. Various mechanical measurements have been performed to characterize this vibration. To this aim, a new test stand has been designed. The analysis of the Campbell diagram shows that the vibration is related to a backward-whirl vibrational mode of the rotor which is always present, with different amplitudes depending on the operating conditions and configuration. Modifications of the shroud roughness and insertion of small obstacles in the gap region have independently shown that leakage flow fluctuations constitute the excitation of the large-amplitude vibration. This indicates that the phenomenon is likely an aeroelastic flutter, as it is also suggested by the observed intermittency and aerodynamic stiffening. A complete series of aerodynamic measurements have been carried out, employing complementary techniques (PIV and LDA), to supply general information on the flow as well as deepen the unsteady flow involved in the flutter phenomenon. The PIV measurements have shown a recirculating flow downstream of the fan due to the presence of the obstruction disk which results in a backflow entering the gap between the rotating ring and the stationary shroud (the leakage flow). Large-scale eddies have been found at the edge and inside of this recirculating flow by investigating the PIV snapshots and have been proved by POD analysis. The LDA measurements close to the gap region have confirmed that the leakage flow enters from the gap downstream of the fan and mixes with the rotor inflow upstream of the fan when it leaves the gap. Using a new double phase ensemble average technique, the periodic part of the LDA signals related to the vibration has been investigated; it allows studying the effect of the precession motion of the rotor on the flow. Analyzing the flow using this method shows that the flutter also affects the relative flow angle at the rotor inlet, and consequently the angle of attack at the blade tips, which finally causes the aeroelastic phenomenon. Moreover, it has been found that the maxima and minima in the velocity field are located at angular positions different from the ones at which the gap outlet area is maximum and minimum, but a certain delay exists

Aeronautical Engineering. A continuing bibliography with indexes, supplement 156

This bibliography lists 288 reports, articles and other documents introduced into the NASA scientific and technical information system in December 1982

Particle image velocimetry study of a skid steer loader cooling fan

Reducing noise generation in construction and farm machinery has become increasingly necessary to comply with stringent noise regulations. This need is particularly challenging in the design of skid steer loaders where machine space is tightly allocated, and the operator is close to the noise sources. In this thesis, particle image velocimetry (PIV) is used to study airflow in a skid steer loader\u27s cooling package with an emphasis on gaining insights into strategies for noise reduction. The centrifugal fan used in this package is installed in a blower housing with two outlets and one inlet. PIV data were taken near the fan on both sides of the blower housing. Ensembles of images were collected both at specified fan positions and randomly to obtain an average of the flow. Sound experiments were also performed to ascertain the result of various conditions. Experiments with the production fan and blower housing suggested that the system is operating under substantial restriction. Various strategies for investigating blower performance were investigated. These included a volute insert and fans with altered blade shapes and with impeller shrouds attached to the blades opposite the base plate. The volute consistently increased the sound produced when it was used due to the volute tongue interacting with the fan. Both fans with rings reduced noise production with the greatest reduction for the fan with the larger ring. The effectiveness of the individual fan blades was studied by collecting data at twenty-seven evenly spaced fan positions over one revolution of the fan. The data suggested that the fan blades were performing similarly. Finally, mean flow data were collected in the near-fan region of the blower housing without the volute cutoff and indicated reingestion of flow into the fan. A volute was produced based on the PIV data to prohibit this reingestion. The volute stopped the recirculation but caused increased noise and decreased flow

Laser Diagnostic System Validation and Ultra-Compact Combustor Characterization

The AFIT combustion optimization and analysis laser (COAL) lab is now completely operational and is state-of-the-art in combustion diagnostics. The objective of this research is to perform a validation of a laser diagnostic system and to begin the characterization of a small-scale model of an ultra-compact combustor (UCC). Validation of the laser system was accomplished by using planar laser induced fluorescence (PLIF) on a laminar premixed hydrogen-air flame produced by a Hencken burner. OH species concentrations are measured. Flame temperatures are determined with a two line fluorescence technique using different transitions in the (1,0) band of the OH (A-X) electronic transition system. Comparisons are made to existing research to prove accuracy. Characterization of the UCC began by developing an operational procedure. A proper starting condition and operating regime has been established. Pressures, temperature, and emissions data have been recorded for a range of equivalence ratios. Comparisons are made to previous computational fluid dynamic (CFD) research. Combustion efficiencies of over 99% have been recorded when operating the small-scale UCC. Future work will involve using PLIF to take non-intrusive measurements inside the combustor through optically clear quartz windows to study cavity-vane interactions

Turbulent flow in rib-roughened channel under the effect of Coriolis and rotational buoyancy forces

The turbulent flow inside a rotating channel provided with transverse ribs along one wall is studied by means of two-dimensional time-resolved particle image ve- locimetry. The measurement set-up is mounted on the same rotating disk with the test section, allowing to obtain the same accuracy and resolution as in a non-rotating rig. The Reynolds number is 15 000, and the rotation number is 0.38. As the ribbed wall is heated, both the Coriolis force and the centrifugal force play a role in the fluid dynamics. The mean velocity fields highlight the major impact of the rotational buoyancy (characterized by a buoyancy number of 0.31) on the flow along the lead- ing side of the duct. In particular, since the flow is directed radially outward, the near-wall layers experience significant centripetal buoyancy. The recirculation area behind the obstacles is enlarged to the point of spanning the whole inter-rib space. Also the turbulent fluctuations are significantly altered, and overall augmented, with respect to the non-buoyant case, resulting in higher turbulence levels far from the rib. On the other hand the centrifugal force has little or no impact on the flow along the trailing wall. Vortex identification, proper orthogonal decomposition, and two-point correlations are used to highlight rotational effects, and in particular to determine the dominant scales of the turbulent unsteady flow, the time-dependent behavior of the shear layer and of the recirculation bubble behind the wall-mounted obstacles, the lifetime and advection velocity of the coherent structures

Characterization of Centrifugally-Loaded Flame Migration for Ultra-Compact Combustors

The Air Force Research Laboratory (AFRL) has designed an Ultra Compact Combustor (UCC) showing viable merit for significantly reducing gas turbine combustor length making it a viable candidate for implementation as an inter-turbine burner and realization of efficiency benefits from the resulting near constant temperature cycle. This concept uses an off-axis combustor cavity and projects approximately 66% length reduction over a conventional combustor. The annular nature of the cavity creates high angular acceleration levels, on the order of 500-3500 g\u27s, resulting in strong centrifugal and buoyant forces. This unique combination works to significantly reduce the required burn time and subsequently required combustor size. However, currently tested experimental models are in the 10-20 cm diameter range while application to larger-scale commercial and military engines would require a UCC in the 50-60 cm diameter range. The Air Force Institute of Technology\u27s Combustion Optimization and Analysis Laser (COAL) laboratory was specifically designed to study the underlying UCC dynamics and investigate the feasibility of scaling the UCC to the significantly larger diameter range. Using a sectional model of AFRL\u27s annular UCC allows customization of the UCC model to investigate varying several parameters of interest associated with the UCC scaling. Several diagnostic methods were used such as Particle Image Velocimetry (PIV) for flowfield measurements, two-line Planar Laser-Induced Fluorescence (PLIF) of the hydroxyl (OH) radical for 2-D temperature profiles, single-line PLIF for qualitative flame location, and high-speed video to investigate flame migration trajectory

Aeronautical engineering: A continuing bibliography with indexes (supplement 303)

This bibliography lists 211 reports, articles, and other documents introduced into the NASA scientific and technical information database. Subject coverage includes: design, construction, and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics