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  • FLUID MECHANICS AND HEAT TRANSFER  (2,603)
  • 1980-1984  (1,490)
  • 1975-1979  (1,113)
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Year
  • 1
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    Determination of the transition point in a boundary layer by the measurement of pressure fluctuation (1981)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A method is developed for determining the laminar-to-turbulent transition point in a boundary layer. The method involves the measurement of pressure on the surface of the body and the computation of pressure fluctuations. This method of determining the transition point is suitable when visualization methods cannot be used.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-76639
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    On the electrical heating of wires in rarefied gases by an electric current (1981)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Experimental work to determine the temperature dependence of the heat loss of thin wires in hydrogen is described. An explanation for the peculiar form of the current voltage curve is provided.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-76597
    Format: application/pdf
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  • 3
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    The influence of a local wall deformation on the development of natural instabilities in a laminar boundary layer (1981)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The natural instabilities which propagate in the laminar boundary layer of a flat plate composed of intermittent wave trains are described. A spectral analysis determines the frequency range and gives a frequency and the harmonic 2 only if there is a wall deformation. This analysis provides the amplitude modulation spectrum of the instabilities. Plots of the evolution of power spectral density are compared with the numerical results obtained from the resolve of the Orr-Sommerfeld equation, while the harmonic is related to a micro-recirculating flow near the wall deformation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-76558
    Format: application/pdf
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  • 4
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    The hydrodynamic role of fish squamosal integument as an analog of surfaces directly formed by turbulent flow. Report 1: Similarity between irregularities in squamosal integument and those on surfaces formed by river bed flow (1980)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The distribution of squamae on the fish body and that of the deposits in the bed of the river can be described by the same equation. The curves reflecting the relative elongation and stability of the body shape of the fish continue the curves showing the elongation of bank spit and stability of the bed of the river.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-75390
    Format: application/pdf
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  • 5
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    First results of a study on turbulent boundary layers in oscillating flow with a mean adverse pressure gradient (1979)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The development of a turbulent unsteady boundary layer with a mean pressure gradient strong enough to induce separation, in order to complete the extend results obtained for the flat plate configuration is presented. The longitudinal component of the velocity is measured using constant temperature hot wire anemometer. The region where negative velocities exist is investigated with a laser Doppler velocimeter system with BRAGG cells. The boundary layer responds by forced pulsation to the perturbation of potential flow. The unsteady effects observed are very important. The average location of the zero skin friction point moves periodically at the perturbation frequency. Average velocity profiles from different instants in the cycle are compared. The existence of a logarithmic region enables a simple calculation of the maximum phase shift of the velocity in the boundary layer. An attempt of calculation by an integral method of boundary layer development is presented, up to the point where reverse flow starts appearing.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-75799 , Colloq. d''Aerodyn. Appl.; Nov 07, 1978 - Nov 09, 1978; Marseille
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  • 6
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    Experimental investigation of turbulent flow in smooth and longitudinal grooved tubes (1984)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Turbulent flow in tubes with and without longitudinal grooves is examined. The discovery of fine grooves forming a sort of streamline pattern on the body of sharks led to the expectation that the grooves on a surface reduce the momentum change, and thus the drag. To test this thesis, drag law, velocity profile and the profile of the velocity fluctuation were determined. Results show that for moderate Reynolds numbers the drag coefficient for grooved tubes is about 3 percent smaller than that of the smooth tubes. At higher Reynolds numbers, however, the drag coefficient for grooved tubes becomes larger than that for smooth tubes. No significant differences in the velocity profiles between grooved tubes and smooth tubes are found.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-77480 , NAS 1.15:77480
    Format: application/pdf
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  • 7
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    Existence of a natural instability not predicted by theory and connected to a wall deformation in a laminar boundary layer (1981)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Natural instability related to negative wall deformation was studied. It was shown that natural instabilities which propagate in a laminar boundary layer of a flat plate are in agreement with stability theory. It is found that if a wall has a deformation, a second frequency does exist, which is not predicted and is twice the first frequency. This second instable frequency only appears if there is a negative velocity gradient. The phenomenon is located very closely to the wall and drops off rapidly when moved away from it.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-76559
    Format: application/pdf
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  • 8
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    An experimental investigation on the subcritical instability in plane Poieseuille flow (1981)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The relationship between the three dimensional properties of the fundamental flow of a plane Poieseuille flow and subcritical stability was studied. An S-T wave was introduced into the flow and the three dimensional development of the wave observed. Results indicate that: (1) the T-S wave has three dimensional properties which are synchronous with the fundamental flow, but there is damping at microamplitude; (2) when the amplitude reaches a certain threshold, subcritical instability and peak valley bifurcation occur simultaneously and a peak valley structure is formed; (3) this threshold depends to a great extent on the frequency; and (4) after the peak valley bifurcation there is a transition to a turbulent flow by the process of laminar flow collapse identical to that in Blasius flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-75885
    Format: application/pdf
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  • 9
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    Studies on the influence on flexural wall deformations on the development of the flow boundary layer (1978)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Flexural wave-like deformations can be used to excite boundary layer waves which in turn lead to the onset of turbulence in the boundary layer. The investigations were performed with flow velocities between 5 m/s and 40 m/s. With four different flexural wave transmissions a frequency range from 0.2 kc/s to 1.5 kc/s and a phase velocity range from 3.5 m/s to 12 m/s was covered. The excitation of boundary layer waves becomes most effective if the phase velocity of the flexural wave coincides with the phase velocity region of unstable boundary layer waves.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-75220
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  • 10
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    Experimental study of the laminar-turbulent transition of a concave wall in a parallel flow (1978)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: The instability of the laminar boundary layer flow along a concave wall was studied. Observations of these three-dimensional boundary layer phenomena were made using the hydrogen-bubble visualization technique. With the application of stereo-photogrammetric methods in the air-water system it was possible to investigate the flow processes qualitatively and quantitatively. In the case of a concave wall of sufficient curvature, a primary instability occurs first in the form of Goertler vortices with wave lengths depending upon the boundary layer thickness and the wall curvature. At the onset the amplification rate is in agreement with the linear theory. Later, during the non-linear amplification stage, periodic spanwise vorticity concentrations develop in the low velocity region between the longitudinal vortices. Then a meandering motion of the longitudinal vortex streets subsequently ensues, leading to turbulence.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-75243
    Format: application/pdf
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