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  • 1
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    Boundary regularized integral equation formulation of Stokes flow (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-02-06
    Description: Single-phase Stokes flow problems with prescribed boundary conditions can be formulated in terms of a boundary regularized integral equation that is completely free of singularities that exist in the traditional formulation. The usual mathematical singularities that arise from using the fundamental solution in the conventional boundary integral method are removed by subtracting a related auxiliary flow field, w , that can be constructed from one of many known fundamental solutions of the Stokes equation. This approach is exact and does not require the introduction of additional cutoff parameters. The numerical implementation of this boundary regularized integral equation formulation affords considerable savings in coding effort with improved numerical accuracy. The high accuracy of this formulation is retained even in problems where parts of the boundaries may almost be in contact.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Linear stability of pressure-driven flow over longitudinal superhydrophobic grooves (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-02-02
    Description: The modal analysis of pressure-driven flows in channels patterned with superhydrophobic surfaces containing periodic grooves and ribs aligned longitudinally to the flow direction has been performed. The effects of shear–free fraction δ and groove-rib spatial period normalized by full-channel height L on the linear flow stability of such flows have been explored. By performing a BiGlobal linear stability analysis via the pseudo-spectral method, such surfaces have been found to potentially exert a stabilizing or destabilizing effect on the base flow, depending predominantly on the normalized groove-rib spacing. For small values of L (i.e., L = 0.01 and 0.02), a stabilizing effect is predicted for flows over longitudinal superhydrophobic grooves, in agreement with the results obtained using a local stability analysis which employs a homogeneous slip condition along the walls. For a moderate value of normalized groove-rib spacing where the groove-rib periodic spacing is one-tenth of the channel height, the presence of longitudinal superhydrophobic grooves leads to flow instabilities at a lower critical Reynolds number. The redistribution of the base flow resulting from the vanishing shear rates along the liquid-gas interface could give rise to an inflectional instability that promotes temporal instability. The effects of patterning the superhydrophobic surfaces on one or both channel walls are also examined.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Differential regulation of RNA polymerases I, II, and III by the TBP-binding repressor Dr1 (1994)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 1994-10-21
    Description: RNA polymerases I, II, and III each use the TATA-binding protein (TBP). Regulators that target this shared factor may therefore provide a means to coordinate the activities of the three nuclear RNA polymerases. The repressor Dr1 binds to TBP and blocks the interaction of TBP with polymerase II- and polymerase III-specific factors. This enables Dr1 to coordinately regulate transcription by RNA polymerases II and III. Under the same conditions, Dr1 does not inhibit polymerase I transcription. By selectively repressing polymerases II and III, Dr1 may shift the physiological balance of transcriptional output in favor of polymerase I.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉White, R J -- Khoo, B C -- Inostroza, J A -- Reinberg, D -- Jackson, S P -- Wellcome Trust/United Kingdom -- New York, N.Y. -- Science. 1994 Oct 21;266(5184):448-50.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Wellcome/CRC Institute, University of Cambridge, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/7939686" target="_blank"〉PubMed〈/a〉
    Keywords: Base Sequence ; DNA-Binding Proteins/metabolism ; HeLa Cells ; Humans ; Molecular Sequence Data ; Phosphoproteins/metabolism/*pharmacology ; RNA Polymerase I/*metabolism ; RNA Polymerase II/*metabolism ; RNA Polymerase III/*metabolism ; Saccharomyces cerevisiae Proteins ; TATA Box ; TATA-Binding Protein Associated Factors ; TATA-Box Binding Protein ; Transcription Factor TFIIB ; Transcription Factor TFIIIB ; Transcription Factors/metabolism/*pharmacology ; *Transcription Factors, TFIII ; Transcription, Genetic/*drug effects
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Investigation of airfoil leading edge separation control with nanosecond plasma actuator (2016)
    American Physical Society (APS)
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    Publication Date: 2016-11-23
    Description: Author(s): J. G. Zheng, Y. D. Cui, Z. J. Zhao, J. Li, and B. C. Khoo A thorough combined numerical and experimental investigation of nanosecond dielectric barrier discharge actuation provides a description of the dynamics of the flow actuation process and elucidates the associated flow control mechanisms. [Phys. Rev. Fluids 1, 073501] Published Tue Nov 22, 2016
    Keywords: Flow control
    Electronic ISSN: 2469-990X
    Topics: Physics
    Published by American Physical Society (APS)
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  • 5
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    Interaction of a spark-generated bubble with a rubber beam: Numerical and experimental study (2012)
    American Physical Society (APS)
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    Publication Date: 2012-08-14
    Description: Author(s): S. W. Gong, B. H. T. Goh, S. W. Ohl, and B. C. Khoo In this paper, the physical behaviors of the interaction between a spark-generated bubble and a rubber beam are studied. Both numerical and experimental approaches are employed to investigate the bubble collapse near the rubber beam (which acts as a flexible boundary) and the corresponding large def... [Phys. Rev. E 86, 026307] Published Mon Aug 13, 2012
    Keywords: Fluid dynamics
    Print ISSN: 1539-3755
    Electronic ISSN: 1550-2376
    Topics: Physics
    Published by American Physical Society (APS)
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  • 6
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    Stability of radial swirl flows (2012)
    Institute of Physics (IOP)
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    Publication Date: 2012-11-29
    Description: The energy gradient theory is used to examine the stability of radial swirl flows. It is found that the flow of free vortex is always stable, while the introduction of a radial flow will induce the flow to be unstable. It is also shown that the pure radial flow is stable. Thus, there is a flow angle between the pure circumferential flow and the pure radial flow at which the flow is most unstable. It is demonstrated that the magnitude of this flow angle is related to the Re number based on the radial flow rate, and it is near the pure circumferential flow. The result obtained in this study is useful for the design of vaneless diffusers of centrifugal compressors and pumps as well as other industrial devices.
    Print ISSN: 1755-1307
    Electronic ISSN: 1755-1315
    Topics: Geography , Geosciences , Physics
    Published by Institute of Physics (IOP)
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  • 7
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    Mechanics of drag reduction by shallow dimples in channel flow (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-03-17
    Description: Arrays of shallow dimples with depth to diameter ratios of 1.5% and 5% are studied in a turbulent channel flow at Reynolds numbers between 5000 and 35 000. Pressure measurements show that drag reduction of up to 3% is possible. The mechanism of skin friction drag reduction with dimples is the same as that observed for flat surfaces using active methods such as spanwise wall motions or transverse wall jets. The three dimensional dimples introduce streamwise vorticity into the flow which results in spanwise flow components near the wall. The result is that the normal energy cascade to the smaller scales is suppressed, which leads to a reduction in turbulent skin friction drag because of the stabilized flow. Increasing the dimple depth from 1.5% to 5% of its diameter increases the streamwise vorticity introduced, which leads to a greater reduction in skin friction. However, increasing the dimple depth also results in flow separation which increases form drag. The net effect to the total drag depends on the relative dominance between the drag reducing streamwise vorticity and the drag increasing flow separation region. As the Reynolds number increases, the region of flow separation can shrink and result in increasing drag reduction. By understanding the flow physics of drag reduction in dimples, there is opportunity to minimize the form drag by passive contouring of the dimples using non-spherical shapes to optimize the dimple performance.
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 8
    Electronic Resource
    Electronic Resource
    A time-resolved hot-wire shear stress probe for turbulent flow: use of laminar flow calibration (1994)
    Springer
    Experiments in fluids 17 (1994), S. 75-83 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A specially-designed rotating rig for producing near Couette flow was used in the calibration of a marginally elevated hot-wire shear stress probe. The probe was then used for measurements in both the turbulent boundary layer and pipe flows. Results showed that the mean wall shear stress can be accurately predicted and the near wall statistical quantities of intensity, skewness and flatness of shear stress fluctuations concurred well with previous works, thereby supporting the notion of a time-resolved shear stress probe for turbulent flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02412806
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Turbulence structure in the immediate vicinity of the shear-free air–water interface induced by a deeply submerged jet (1999)
    Springer
    Experiments in fluids 27 (1999), S. 321-331 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  A PIV based technique is developed to perform flow measurements in the vicinity of the air–water interface of a submerged confined jet. Both the interface movement and the velocity field immediately beneath it are measured simultaneously. A detailed turbulence structure in the surface influence region is thus obtained. Flow parameters evaluated without and w.r.t. the interface are quantified and compared against previous works obtained using the conventional Eulerian-based instrumentation which do not account for the interface fluctuation, and checked against analytical model characterising the turbulence close to a assumed flat air–water interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003480050356
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  • 10
    Electronic Resource
    Electronic Resource
    Skin Friction following BLADE manipulation in a turbulent pipe flow (1993)
    Springer
    Experiments in fluids 15 (1993), S. 274-278 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This study attempts to analyze the measured wall shear stress distribution downstream of single and tandem BLADEs in fully developed pipe flow. Previous works have indicated the adverse effect of overall drag increase with the single BLADE in both channel and pipe flows, and an even larger drag increase with the tandem BLADES. This is contrary to that observed for external boundary layer flow. Extensive comparisons are then made to the wall shear stress distribution following BLADEs in boundary layer flow, leading to the conclusion of little or no potential in the application of BLADEs alone to pipe flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223405
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