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  • Other Sources  (12)
  • 2010-2014  (4)
  • 1990-1994  (8)
  • 1
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    The effects of streamline curvature and swirl on turbulent flows in curved ducts (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A technique for improving the numerical predictions of turbulent flows with the effect of streamline curvature is developed. Separated flows, the flow in a curved duct, and swirling flows are examples of flow fields where streamline curvature plays a dominant role. A comprehensive literature review on the effect of streamline curvature was conducted. New algebraic formulations for the eddy viscosity incorporating the kappa-epsilon turbulence model are proposed to account for various effects of streamline curvature. The loci of flow reversal of the separated flows over various backward-facing steps are employed to test the capability of the proposed turbulence model in capturing the effect of local curvature. The inclusion of the effect of longitudinal curvature in the proposed turbulence model is validated by predicting the distributions of the static pressure coefficients in an S-bend duct and in 180 degree turn-around ducts. The proposed turbulence model embedded with transverse curvature modification is substantiated by predicting the decay of the axial velocities in the confined swirling flows. The numerical predictions of different curvature effects by the proposed turbulence models are also reported.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-187759 , NAS 1.26:187759 , KU-FRL-793-1
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  • 2
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    Structure and Soot Properties of Non-Buoyant Laminar Round-Jet Diffusion Flames (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The structure and soot properties of nonbuoyant laminar diffusion flames are being studied experimentally and theoretically in order to better understand the soot and thermal radiation emissions from luminous flames. The measurements involve weakly-buoyant flames at low pressure in normal gravity (ng) and nonbuoyant flames at normal pressures in microgravity (micro g). The objectives of the present investigation are to study the differences of soot properties between nonbuoyant and buoyant diffusion flames, and to evaluate predictions based on the laminar flamelet approach.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: NASA. Lewis Research Center, The Second International Microgravity Combustion Workshop; p 107-113
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  • 3
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    Spectral analysis of unsteady surface pressure on a pusher propeller (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A propeller of an advanced turboprop testbed aircraft in pusher configuration is instrumented with 22 miniature blade-mounted transducers (BMTs) at two radii. Upstream pylon wake interaction with the propeller is the source of a one-per-cycle excitation for the blades in flight. The time history of fluctuating pressure signals over 26 flight conditions is statistically analyzed in the frequency domain. The rms amplitude of fluctuating pressure signals measured by suction surface BMTs indicates a very strong presence of the fundamental frequency over most of the upper surface. The pylon wake pressure signature on the propeller trailing edge, i.e., x/c not less than 0.80, shows predominantly random turbulence; hence, the amplitude of the fundamental frequency wave is fairly small. The resurgence of a large amplitude fundamental harmonic with coherent pylon wake signature further downstream, say at 90 percent chord, is unexpected behavior. The appearance of a dominating second propeller shaft order in the spectra of the rms pressure in transonic flight conditions identifies the presence of a two-per-cycle excitation source in the azimuthal direction. This is due to the presence of a shock wave, as evidenced by the pressure-time history plots.
    Keywords: AERODYNAMICS
    Type: In: Rotating machinery - Transport phenomena; Proceedings of the 3rd International Symposium on Transport Phenomena and Dynamics of Rotating Machinery (ISROMAC-3), Honolulu, HI, Apr. 1-4, 1990 (A93-54; p. 665-680.
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  • 4
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    A study of three dimensional turbulent boundary layer separation and vortex flow control using the reduced Navier Stokes equations (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A reduced Navier-Stokes (RNS) initial value space marching solution technique was applied to vortex generator and separated flow problems and demonstrated good predictions of the engine face flow field. This RNS solution technique using FLARE approximations can adequately describe the topological and topographical structure flow separation associated with vortex liftoff, and this conclusion led to the concept of a subclass of separations which can be called vorticity separations: separations dominated by the transport of vorticity. Adequate near wall resolution of vorticity separations appears necessary for good predictions of these flows.
    Keywords: AERODYNAMICS
    Type: Symposium on Turbulent Shear Flows; Sept. 9-11, 1991; Munich; Germany
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  • 5
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    Modern developments in shear flow control with swirl (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Passive and active control of swirling turbulent jets is experimentally investigated. Initial swirl distribution is shown to dominate the free jet evolution in the passive mode. Vortex breakdown, a manifestation of high intensity swirl, was achieved at below critical swirl number (S = 0.48) by reducing the vortex core diameter. The response of a swirling turbulent jet to single frequency, plane wave acoustic excitation was shown to depend strongly on the swirl number, excitation Strouhal number, amplitude of the excitation wave, and core turbulence in a low speed cold jet. A 10 percent reduction of the mean centerline velocity at x/D = 9.0 (and a corresponding increase in the shear layer momentum thickness) was achieved by large amplitude internal plane wave acoustic excitation. Helical instability waves of negative azimuthal wave numbers exhibit larger amplification rates than the plane waves in swirling free jets, according to hydrodynamic stability theory. Consequently, an active swirling shear layer control is proposed to include the generation of helical instability waves of arbitrary helicity and the promotion of modal interaction, through multifrequency forcing.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-186586 , NAS 1.26:186586 , KU-FRL-724-4
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  • 6
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    Development of an Integrated Countermeasure Device for Use in Long-Duration Space Flight (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: Prolonged weightlessness is associated with declines in musculoskeletal, cardiovascular, and sensorimotor health. Consequently, in-flight countermeasures are required to preserve astronaut health. We developed and tested a novel exercise countermeasure device (CCD) for use in spaceflight with the aim of preserving musculoskeletal and cardiovascular health along with an incorporated balance-training component. Additionally, the CCD features a compact footprint, and a low power requirement. Methods: After design and development of the CCD, we carried out a training study to test its ability to improve cardiovascular and muscular fitness in healthy volunteers. Fourteen male and female subjects (41.4+/-9.0 years, 69.5+/-15.4Kg) completed 12 weeks (3 sessions per week) of concurrent strength and endurance training on the CCD. Subjects were tested at baseline and after 12 weeks for 1-repetition max leg press strength (1RM), peak oxygen consumption (VO2peak), and isokinetic joint torque (ISO) at the hip, knee, and ankle. Additionally, we evaluated subjects after 6 weeks of training for changes in VO2peak and 1RM. Results: VO2peak and 1RM improved after 6-weeks, with additional improvements after 12 weeks (1.95+/-0.5, 2.28+/-0.5, 2.47+/-0.6 LY/min and 131.2+/-63.9,182.8+/-75.0, 207.0+/-75.0 Kg) for baseline, 6 weeks, and 12 weeks respectively. ISO for hip adduction, adduction, and ankle plantar flexion improved after 12 weeks of training (70.3+/-39.5, 76.8+/-39.2 and 55.7+/-21.7 N-m vs. 86.1+/-37.3, 85.1+/-34.3 and 62.1+/-26.4 N-m respectively). No changes were observed for ISO during hip flexion, knee extension, or knee flexion. Conclusions: The CCD is effective at improving cardiovascular fitness and isotonic leg strength in healthy adults. Further, the improvement in hip adductor and abductor torque provides support that the CCD may provide additional protection for the preservation of bone health at the hip.
    Keywords: Aerospace Medicine
    Type: JSC-CN-21987
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  • 7
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    On the aerodynamics and performance of active vortex generators (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: As a building block in the development of smart lift-enhancement devices, a new concept for flow control using active vortex generators (AVGs) is presented. Ramp, wedge, and doublet wedge (Wheeler) VG configurations are investigated. The AVGs are designed to conform to the surface of the wing section at low alpha. As the section approaches the stall, they are deployed and accordingly, alpha(stall) and C(lmax) are increased. A qualitative analysis of the flow around the various VG configurations was conducted in a low speed wind tunnel at 1.6 ft/s and a Reynolds number of approximately 3400. The results demonstrate that ramp VGs produce vortices that have the longest distance at breakdown. The VGs were also applied to a 25-in. span, 8-in. chord NACA 4415 wing section. Optimization studies were conducted on the spanwise spacing, chordwise position, and size of statically deployed VGs. The test results demonstrate a 14-percent increase in C(lmax) while increasing alpha (stall) by up to 3.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 93-3447 , In: AIAA Applied Aerodynamics Conference, 11th, Monterey, CA, Aug. 9-11, 1993, Technical Papers. Pt. 1 (A93-47201 19-02); p. 376-386.
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  • 8
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    An Integrated Musculoskeletal Countermeasure Battery for Long-Duration Lunar Missions (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: During extended periods of skeletal unloading, losses in strength and density of the proximal femur will occur. In long-duration spaceflight, resistive exercise is used to replace the normal loads exerted on the spine and hip. At the present time, there is no conclusive evidence that hip bone loss has been prevented in this scenario. Our group has recently developed and clinically evaluated a multifunctional exercise system, the Combined Countermeasure Device (CCD). The CCD comprises a low-footprint Stuart Platform for lower-body resistance exercise and balance training, and a cardiovascular exercise bicycle. A consideration for resistance exercise was targeting of the hip abductor and adductor muscles, which attach directly at the hip and which should subject it to the largest loads. In our training study, we found that CCD exercise increased hip adductor and abductor strength, and modeling results suggest that this exercise exerts forces on the hip of approx. 4-6 body weights at 1g, compared to forces of approx.2.5 body weight y squatting exercise. In our current study, we hypothesize that abductor and adductor exercise will increase the density and strength of the proximal femur.
    Keywords: Aerospace Medicine
    Type: JSC-CN-25294 , 2012 NASA Human Research Program Investigators'' Workshop; Feb 14, 2012 - Feb 16, 2012; Houston, TX; United States
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  • 9
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    A study of three dimensional turbulent boundary layer separation and vortex flow control using the reduced Navier Stokes equations (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A reduced Navier Stokes (RNS) initial value space marching solution technique was applied to vortex generator and separated flow problems and demonstrated good predictions of the engine face flow field. This RNS solution technique using FLARE approximations can adequately describe the topological and topographical structure flow separation associated with vortex liftoff, and this conclusion led to the concept of a subclass of separations which can be called vorticity separations: separations dominated by the transport of vorticity. Adequate near wall resolution of vorticity separations appears necessary for good predictions of these flows.
    Keywords: AERODYNAMICS
    Type: NASA-TM-104407 , E-6233 , NAS 1.15:104407 , Turbulent Shear Flow Symposium; Sep 09, 1991 - Sep 11, 1991; Munich; Germany
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  • 10
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    Pressure-time history of pylon wake on a pusher propeller in flight (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Keywords: ACOUSTICS
    Type: Journal of Propulsion and Power (ISSN 0748-4658); 6; 758-768
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