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  • AERODYNAMICS  (3)
  • FLUID MECHANICS AND HEAT TRANSFER  (3)
  • 1
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    The influence of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-177520 , NAS 1.26:177520
    Format: application/pdf
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  • 2
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    Effects of free-stream turbulence on diffuser performance (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An experimental evaluation of the effects of free stream turbulence on the performance of a subsonic two dimensional diffuser was made. The diffuser's static pressure recovery coefficient was increased 11.4 and 21.1 percent at total. Divergence angles of 12 and 20 degrees respectively were obtained when the value of the inlet integral free stream scale of turbulence in the flow direction was at least 7.5 times larger than the inlet boundary layer displacement thickness, and when the inlet total free stream turbulence intensity was at least 3.5 percent. It is hypothesized that a larger scale of turbulence transmits the free stream energy to the wall more effectively and when coupled with large turbulence intensities, acts to decrease the distortion and delay separation within the diffuser.
    Keywords: AERODYNAMICS
    Type: NASA-CR-163194
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  • 3
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    Effects of small-scale, high intensity inlet turbulence on flow in a two-dimensional diffuser (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The flow through a 2D experimental diffuser with channel width 2.60 cm and divergence angle (2 theta) 9 or 20 deg is investigated experimentally for inlet Reynolds number 78,300 and velocity 43.9 m/s, with and without vertical rods to generate inlet turbulence in excess of the limits defined by Hoffmann (1981) and Hoffmann and Gonzales (1983). Measurements are obtained using a thermal wall-flow-direction probe and a single hot-wire velocity probe, and the results are presented graphically. Significant increases in the pressure-recovery coefficient of the diffuser (10 percent at 9 deg and 22 percent at 20 deg) are attributed to the action of turbulence to reduce distortion and delay separation, thus creating an altered flow condition with symmetrical velocity profiles.
    Keywords: AERODYNAMICS
    Type: ASME, Transactions, Journal of Fluids Engineering (ISSN 0098-2202); 106; 121-124
    Format: text
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  • 4
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    Effects of free-stream turbulence on diffuser performance (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An experimental evaluation of the effects of free-stream turbulence on the performance of a subsonic two-dimensional diffuser has been made. Increases of the diffuser's static pressure recovery coefficient of 11.3 and 23.9 percent at total included divergence angles of 12 and 20 degrees respectively were obtained when the value of the inlet integral free-stream scale of turbulence in the flow direction was at least 7.2 times larger than the inlet boundary layer displacement thickness, when the inlet total free-stream turbulence intensity was at least 3.5 percent, and when the axes of upstream rods used to generate turbulence were perpendicular to the flow and parallel to the diverging walls of the diffuser. It is hypothesized that a larger scale of turbulence with the specified eddy axis orientation transmits the free-stream energy to the walls more effectively and, when coupled with large turbulence intensities, are mechanisms which act to decrease the distortion and delay separation within the diffuser.
    Keywords: AERODYNAMICS
    Type: ASME PAPER 81-FE-4
    Format: text
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  • 5
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    Effects of free-stream turbulence on turbulent boundary layers with mild adverse pressure gradients (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The influence of near isotropic free-stream turbulence on the shape factors and skin friction coefficients of turbulent boundary layers is presented for the cases of zero and mild adverse pressure gradients. With free-stream turbulence, improved fluid mixing occurs in boundary layers with adverse pressure gradients relative to the zero pressure gradient condition, with the same free-stream turbulence intensity and length scale. Stronger boundary layers with lower shape factors occur as a result of a lower ratio of the integral scale of turbulence to the boundary layer thickness, and to vortex stretching of the turbulent eddies in the free-stream, both of which act to improve the transmission of momentum from the free-stream to the boundary layers.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 88-3757 , AIAA, ASME, SIAM, and APS, National Fluid Dynamics Congress; Jul 25, 1988 - Jul 28, 1988; Cincinnati, OH; United States
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  • 6
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    Flow direction measurement criteria and techniques planned for the 40- by 80-/80- x 120-foot wind tunnel integrated systems tests (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A study was performed in order to develop the criteria for the selection of flow direction indicators for use in the Integrated Systems Tests (ISTs) of the 40 by 80/80 by 120 Foot Wind Tunnel System. The problems, requirements, and limitations of flow direction measurement in the wind tunnel were investigated. The locations and types of flow direction measurements planned in the facility were discussed. A review of current methods of flow direction measurement was made and the most suitable technique for each location was chosen. A flow direction vane for each location was chosen. A flow direction vane that employs a Hall Effect Transducer was then developed and evaluated for application during the ISTs.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-176969 , NAS 1.26:176969
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