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  • 1
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    Acoustic Modeling and Analysis for the Space Shuttle Main Propulsion System Liner Crack Investigation (2004)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: Cracks were found on bellows flow liners in the liquid hydrogen feedlines of several space shuttle orbiters in 2002. An effort to characterize the fluid environment upstream of the space shuttle main engine low-pressure fuel pump was undertaken to help identify the cause of the cracks and also provide quantitative environments and loads of the region. Part of this effort was to determine the duct acoustics several inches upstream of the low-pressure fuel pump in the region of a bellows joint. A finite element model of the complicated geometry was made using three-dimensional fluid elements. The model was used to describe acoustics in the complex geometry and played an important role in the investigation. Acoustic mode shapes and natural frequencies of the liquid hydrogen in the duct and in the cavity behind the flow liner were determined. Forced response results were generated also by applying an edgetone-like forcing to the liner slots. Studies were conducted for state conditions and also conditions assuming two-phase entrapment in the backing cavity. Highly instrumented single-engine hot fire data confirms the presence of some of the predicted acoustic modes.
    Keywords: Spacecraft Design, Testing and Performance
    Type: 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit; Jul 11, 2004 - Jul 14, 2004; Fort Lauderdale, FL; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Assessing Spontaneous Combustion Instability with Recurrence Quantification Analysis (2016)
    In:  CASI
    Details
    Publication Date: 2019-08-13
    Description: Spontaneous instabilities can pose a significant challenge to verification of combustion stability, and characterizing its onset is an important avenue of improvement for stability assessments of liquid propellant rocket engines. Recurrence Quantification Analysis (RQA) is used here to explore nonlinear combustion dynamics that might give insight into instability. Multiple types of patterns representative of different dynamical states are identified within fluctuating chamber pressure data, and markers for impending instability are found. A class of metrics which describe these patterns is also calculated. RQA metrics are compared with and interpreted against another metric from nonlinear time series analysis, the Hurst exponent, to help better distinguish between stable and unstable operation.
    Keywords: Spacecraft Propulsion and Power
    Type: M16-5448 , Modeling and Simulation (MSS) Joint Subcommittee Meeting; Dec 05, 2016 - Dec 08, 2016; Phoenix, AZ; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Dynamics of a 4x6-Meter Thin Film Elliptical Inflated Membrane for Space Applications (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Dynamic characterization of a thin film inflatable elliptical structure is described in detail. A two-step finite element modeling approach in MSC/NASTRAN is utilized, consisting of (1) a nonlinear static pressurization procedure used to obtain the updated stiffness matrix, and (2) a modal "restart" eigen solution that uses the modified stiffness matrix. Unique problems encountered in modeling of this large Hexameter lightweight inflatable arc identified, including considerable difficulty in obtaining convergence in the nonlinear finite element pressurization solution. It was found that the extremely thin polyimide film material (.001 in or 1 mil) presents tremendous problems in obtaining a converged solution when internal pressure loading is applied. Approaches utilized to overcome these difficulties are described. Comparison of finite element predictions for frequency and mode shapes of the inflated structure with closed-form solutions for a flat pre-tensioned membrane indicate reasonable agreement.
    Keywords: Mechanical Engineering
    Type: AIAA Paper 2002-1557 , AIAA Structures, Structural Dynamics, and Materials Conference; Apr 22, 2002 - Apr 25, 2002; Denver, CO; United States
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  • 4
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    Investigation of Combustion Control in a Dump Combustor Using the Feedback Free Fluidic Oscillator (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A feedback free fluidic oscillator was designed and integrated into a single element rocket combustor with the goal of suppressing longitudinal combustion instabilities. The fluidic oscillator uses internal fluid dynamics to create an unsteady outlet jet at a specific frequency. An array of nine fluidic oscillators was tested to mimic modulated secondary oxidizer injection into the combustor dump plane. The combustor has a coaxial injector that uses gaseous methane and decomposed hydrogen peroxide with an overall O/F ratio of 11.7. A sonic choke plate on an actuator arm allows for continuous adjustment of the oxidizer post acoustics enabling the study of a variety of instability magnitudes. The fluidic oscillator unsteady outlet jet performance is compared against equivalent steady jet injection and a baseline design with no secondary oxidizer injection. At the most unstable operating conditions, the unsteady outlet jet saw a 67% reduction in the instability pressure oscillation magnitude when compared to the steady jet and baseline data. Additionally, computational fluid dynamics analysis of the combustor gives insight into the flow field interaction of the fluidic oscillators. The results indicate that open loop high frequency propellant modulation for combustion control can be achieved through fluidic devices that require no moving parts or electrical power to operate.
    Keywords: Computer Programming and Software; Spacecraft Propulsion and Power; Fluid Mechanics and Thermodynamics
    Type: M15-4712 , AIAA/SAE/ASEE Joint Propulsion Conference; Jul 27, 2015 - Jul 29, 2015; Orlando, FL; United States
    Format: application/pdf
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