SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS

A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 43, ISSUE 18 - SEPTEMBER 09, 2005

02 AERODYNAMICS
Includes aerodynamics of flight vehicles, test bodies, airframe components and combinations, wings, and control surfaces.

Also includes aerodynamics of rotors, stators, fans, and other elements of turbomachinery.

For related information see also 34 Fluid Mechanics and Thermodynamics.

20050204122 Hughes Technical Center, Atlantic City International Airport, NJ, USA

Minimum Performance Standard for Aircraft Cargo Compartment Halon Replacement Fire Suppression Systems (2nd Edition)

Reinhardt, J. W.; Jun. 2005; 34 pp.; In English Report No.(s): PB2005-108938; AAR-440; No Copyright; Avail: CASI; A03, Hardcopy

This technical note presents the second update to the minimum performance standards that a Halon 1301 replacement or alternate system for aircraft cargo compartment must meet as part of the aircraft certification procedures. This document replaces report number DOT/FAA/AR-TN03/6. This standard considers gaseous and nongaseous fire suppression systems for full-scale fire testing. This report update includes the corrections made to the aerosol can simulator specifications, acceptance criteria section, and the new criteria for the aerosol can explosion test. In addition, some sections were added to the test requirements to clarify some testing procedures. NTIS

Cargo; Compartments; Fires; Halon; Replacing

20050205647 NASA Glenn Research Center, Cleveland, OH, USA

Fan Stall Flutter Flow Mechanism Studied

Lepicovsky, Jan; Research and Technology 2001; March 2002; 3 pp.; In English; No Copyright; Avail: CASI; A01, Hardcopy

Modern turbofan engines employ a highly loaded fan stage with transonic or low-supersonic velocities in the blade-tip region. The fan blades are often prone to flutter at off-design conditions. Flutter is a highly undesirable and dangerous self-excited mode of blade oscillations that can result in high-cycle fatigue blade failure. The origins of blade flutter are not fully understood yet. Experimental data that can be used to clarify the origins of blade flutter in modern transonic fan designs are very limited. The Transonic Flutter Cascade Facility at the NASA Glenn Research Center was developed to experimentally study the details of flow mechanisms associated with fan flutter. The cascade airfoils are instrumented to measure high-frequency unsteady flow variations in addition to the steady flow data normally recorded in cascade tests. The test program measures the variation in surface pressure in response to the oscillation of one or more of the cascade airfoils. However, during the initial phases of the program when all airfoils were in fixed positions, conditions were found where significant time variations in the pressures near the airfoil leading edges could be observed. Derived from text

Turbofan Engines; Aerodynamic Stalling; Blade Tips; Transonic Flutter; Airfoil Oscillations

20050205809 NASA Glenn Research Center, Cleveland, OH, USA

Effect of Variable Chord Length on Transonic Axial Rotor Performance Investigated

Suder, Kenneth L.; Research and Technology 2001; March 2002; 3 pp.; In English; No Copyright; Avail: CASI; A01, Hardcopy

During the life of any gas turbine, blade erosion is present, especially for those units that are exposed to unfiltered air, such as aviation turbofan engines. The effect of this erosion is to reduce the blade chord progressively from the midspan to the tip region and to roughen and distort the blade surface. The effects of roughness on rotor performance have been documented by Suder et al. and Roberts. These papers indicate that the penalty for leading-edge roughness and erosion can be significant. Turbofan operators, therefore, restore chord length at routine maintenance intervals to regain performance before deterioration is too severe to salvage blades. As the rotor blades erode, the leading edge becomes rough - blunt and distorted from the nominal shape - and the aerodynamic performance suffers. Nominal performance can be recovered by recontouring the leading edges. This process, which inherently shortens the blade chord, can be used until the blade chord erodes to the stall limit. Below this chord length, which varies among engine-compressor types, a decrease of stall margin is likely. After compressor blade rework that includes leading edge recontouring, the blades have different chord lengths, ranging from blades that are near nominal chord length down to those near the stall chord limit. Furthermore, as blades erode below the stall limit, they must be replaced with new blades that have the full nominal chord length. Consequently, a set of compressor blades with varying chord lengths will be installed into each turbofan engine that goes through a complete maintenance cycle. The question arises, ‘Does fan or compressor performance depend on the order in which mixed-chord blades are installed into a fan or compressor disk?’ Derived from text

Compressor Rotors; Chords (Geometry); Transonic Compressors; Turbine Blades; Leading Edges

20050210006 NASA Langley Research Center, Hampton, VA, USA

Parachute Aerodynamics From Video Data

Schoenenberger, Mark; Queen, Eric M.; Cruz, Juan R.; [2005]; 13 pp.; In English; 18th AIAA Aerodynamic Decelerator Systems Technology Conference and Seminar, 23-26 May 2005, Munich, Germany Contract(s)/Grant(s): 23-979-20-10; No Copyright; Avail: CASI; A03, Hardcopy

A new data analysis technique for the identification of static and dynamic aerodynamic stability coefficients from wind tunnel test video data is presented. This new technique was applied to video data obtained during a parachute wind tunnel test program conducted in support of the Mars Exploration Rover Mission. Total angle-of-attack data obtained from video images were used to determine the static pitching moment curve of the parachute. During the original wind tunnel test program the static pitching moment curve had been determined by forcing the parachute to a specific total angle-of -attack and measuring the forces generated. It is shown with the new technique that this parachute, when free to rotate, trims at an angle-of-attack two degrees lower than was measured during the forced-angle tests. An attempt was also made to extract pitch damping information from the video data. Results suggest that the parachute is dynamically unstable at the static trim point and tends to become dynamically stable away from the trim point. These trends are in agreement with limit-cycle-like behavior observed in the video. However, the chaotic motion of the parachute produced results with large uncertainty bands. Author

Parachutes; Aerodynamic Stability; Video Data; Damping; Aerodynamic Coeffýcients

Source: NASA.