Wall-Pressure

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Hyung Jin Sung - One of the best experts on this subject based on the ideXlab platform.

  • Relationship between wall pressure fluctuations and streamwise vortices in a turbulent boundary layer
    Physics of Fluids, 2002
    Co-Authors: Jung-il Choi, Hyung Jin Sung
    Abstract:

    A direct numerical simulation is performed to examine the relationship between wall pressure fluctuations and near-wall streamwise vortices in a spatially developing turbulent boundary layer. It is found that wall pressure fluctuations are closely linked with the upstream quasistreamwise vortices in the buffer region. The maximum correlation occurs with the spanwise displacement from the location of wall pressure fluctuations. The space–time correlation reveals that wall pressure fluctuations lag behind streamwise vorticity in the upstream, while streamwise vorticity lag behind wall pressure fluctuations in the downstream. The contributions of high-amplitude wall pressure event to the turbulent energy production mechanism are examined by the quadrant analysis of Reynolds shear stress.

Gabriele Betz - One of the best experts on this subject based on the ideXlab platform.

  • Study of radial die-wall pressure changes during pharmaceutical powder compaction.
    Drug development and industrial pharmacy, 2011
    Co-Authors: Sameh Abdel-hamid, Gabriele Betz
    Abstract:

    Context: In tablet manufacturing, less attention is paid to the measurement of die-wall pressure than to force–displacement diagrams. Objective: Therefore, the aim of this study was to investigate radial stress change during pharmaceutical compaction. Materials and Methods: The PressterTM, a tablet-press replicator was used to characterize compaction behavior of microcrystalline cellulose (viscoelastic), calcium hydrogen phosphate dihydrate (brittle), direct compressible mannitol (plastic), pre-gelatinized starch (plastic/elastic), and spray dried lactose monohydrate (plastic/brittle) by measuring radial die-wall pressure; therefore powders were compacted at different (pre) compaction pressures as well as different speeds. Residual die-wall pressure (RDP) and maximum die-wall pressure (MDP) were measured. Various tablet physical properties were correlated to radial die-wall pressure. Results and Discussion: With increasing compaction pressure, RDP and MDP (P < 0.0001) increased for all materials, with inc...

Ruiqian Dong - One of the best experts on this subject based on the ideXlab platform.

  • Characterizing the dynamic property of the vortex tail in a gas cyclone by wall pressure measurements
    Fuel Processing Technology, 2010
    Co-Authors: Cuizhi Gao, Guogang Sun, Ruiqian Dong
    Abstract:

    To explore a determination method for cyclone vortex tail, the wall pressures at different axial and radial positions of a cylinder-on-cone cyclone were measured and analyzed by the Fast Fourier Transform (FFT) and probability density analyses in this paper. The cyclone vortex tail was also visualized by a red ink tracer. The results show that the cyclone wall pressure does not change in the cylindrical section and gradually decreases in the conical section. The magnitudes of wall pressure at different azimuths are almost identical, indicating an axisymmetrical wall pressure radial profile in these parts of the cyclone. Whereas in the lower part of the cone and/or the upper part of dipleg, there is a sudden fall of wall pressure and non-axisymmetrical pressure radial profile. The minimum wall pressure occurs at about 270° azimuth in this region. Underneath in the next part of the dipleg, the wall pressure rapidly rises and returns to axisymmetry. These characteristics indicate that the vortex tail is bended to wall, turns around in this region, and can be used as evidences of the vortex tail. The position determined by the pressure measurement is close to the position of the rotating ring observed in the tracing experiment. It is also found that the frequency of the inner vortex is different from that of the outer vortex. The inner vortex flow fluctuates stronger and faster than its outer partner. At the vortex tail zone, the vortex breaks and the inner vortex fluctuation is involved in the wall pressure signal. Therefore, the position and dynamic property of the vortex tail can be well identified from the wall pressure measurement. The pressure measurement could provide some solid experimental basis for assessing relations of natural vortex length.

Jung-il Choi - One of the best experts on this subject based on the ideXlab platform.

  • Relationship between wall pressure fluctuations and streamwise vortices in a turbulent boundary layer
    Physics of Fluids, 2002
    Co-Authors: Jung-il Choi, Hyung Jin Sung
    Abstract:

    A direct numerical simulation is performed to examine the relationship between wall pressure fluctuations and near-wall streamwise vortices in a spatially developing turbulent boundary layer. It is found that wall pressure fluctuations are closely linked with the upstream quasistreamwise vortices in the buffer region. The maximum correlation occurs with the spanwise displacement from the location of wall pressure fluctuations. The space–time correlation reveals that wall pressure fluctuations lag behind streamwise vorticity in the upstream, while streamwise vorticity lag behind wall pressure fluctuations in the downstream. The contributions of high-amplitude wall pressure event to the turbulent energy production mechanism are examined by the quadrant analysis of Reynolds shear stress.

K.m. She - One of the best experts on this subject based on the ideXlab platform.

  • Finite element analysis of wall pressure in imperfect silos
    International Journal of Solids and Structures, 1997
    Co-Authors: Jin Y. Ooi, K.m. She
    Abstract:

    It is generally accepted that the pressures exerted by stored bulk solid on silo walls after filling are closely predicted by the Janssen theory. However, recent experimental observations of silo wall pressure have shown significant deviations from Janssen pressures even after careful symmetrical filling. Both meridional and circumferential variations from the Janssen values have been found, which induce bending of the wall in reinforced concrete silos and high membrane stresses in steel silos. It has been suggested that the presence of geometric imperfections in the silo wall is a likely cause of these pressure variations. However, no rigorous investigation of the effects of uneven surface profile on wall pressures appears to have been performed, though some simple calculations have been produced. This paper presents a finite element study of the effects of a local axisymmetric wall imperfection on pressures acting on the wall of a circular silo. The effects of imperfection height and imperfection geometry on wall pressures are also investigated.