Effect of Cavity Volume on the Flow-Excited Acoustic Resonance of a Shallow Cavity in a Pipe-Line

2015 ◽  
Author(s):  
S. Mohamed ◽  
S. Ziada
Keyword(s):  
Strouhal Number ◽  
Pipe Flow ◽  
Acoustic Resonance ◽  
Black Box ◽  
Cavity Volume ◽  
Maximum Value ◽  
Pipe Line ◽  
Shallow Cavities ◽  
Shallow Cavity ◽  
Flow Through

The effect of cavity volume on the aeroacoustic source generated by fully developed pipe flow through an axisymmetric shallow cavity is investigated experimentally. Nine cavity sizes are studied in three different groups of length, L, to depth, H, ratios (L/H = 1, 2 and 3) with three different cavity volumes for each group of L/H. The Sound Wave Method (SWM) is used to measure the aeroacoustic sources as function of the Strouhal number. This methodology does not require knowledge of the details of the unsteady flow-sound interaction in the cavity region because it considers the cavity as a black box with a dipole sound source or sink. The aeroacoustic source strength and the Strouhal number corresponding to its maximum value are found to increase in a systematic manner as the cavity volume is increased for the same L/H ratio. These results indicate that the aeroacoustic sources of shallow cavities are affected not only by the ratio L/H, but also by the cavity volume.

On the effect of a sharp bend in a fully developed turbulent pipe-flow

1968 ◽  
Vol 34 (3) ◽  
pp. 595-608 ◽  
Author(s):  
M. J. Tunstall ◽  
J. K. Harvey
Keyword(s):  
Secondary Flow ◽  
Pipe Flow ◽  
Secondary Circulation ◽  
Turbulent Pipe Flow ◽  
Sharp Bend ◽  
Random Frequency ◽  
Angle Bend ◽  
Circulatory Flow ◽  
Flow Through ◽  
Upstream Flow

It has been found experimentally that the turbulent pipe flow through a mitred, right-angle bend produces a downstream secondary circulation which does not conform to the twin-circulatory flow usually to be found in pipe bends. The secondary flow is dominated by a single circulation about the axis in either a clockwise or an anticlockwise sense, between which it switches abruptly at a low, random frequency. The phenomenon is explained in terms of the asymmetry of the inner wall separation and the turbulent axial circulation generated in the upstream flow.

Applicability of The Equivalent Diameter Approach to Estimate Vortex Shedding Frequency and Acoustic Resonance Excitation From Different Finned Cylinders In Cross-Flow

2021 ◽  
Author(s):  
Mohammed Alziadeh ◽  
Atef Mohany
Keyword(s):  
Strouhal Number ◽  
Vortex Shedding ◽  
Interaction Mechanism ◽  
Acoustic Resonance ◽  
Resonance Excitation ◽  
Equivalent Diameter ◽  
Effective Diameter ◽  
Finned Tubes ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

Abstract This article explores the applicability of utilizing different equivalent diameter (Deq) equations to estimate the vortex shedding frequency and onset of self-excited acoustic resonance for various types of finned cylinders. The focus is on three finned cylinder types that are commonly used in industrial heat exchangers: straight, twist-serrated, and crimped spirally finned cylinders. Within each type of fins, at least three different finned cylinders are investigated. The results indicate that at off-resonance conditions, utilizing the appropriate equivalent diameter collapses the Strouhal number data within the typical Strouhal number variations of an equivalent diameter circular, bare cylinder. However, when acoustic resonance is initiated, the onset and the peak of resonance excitation in all of the finned cylinder cases generally occurred at a reduced flow velocity earlier than that observed from their equivalent diameter bare cylinders. This suggests that although utilizing the appropriate equivalent diameter can reasonably estimate the vortex shedding frequency away from acoustic resonance excitation, it cannot be used to predict the onset of acoustic resonance in finned tubes. The findings of this study indicate that the effective diameter approach is not sufficient to capture the intrinsic changes in the flow-sound interaction mechanism as a result of adding fins to a bare cylinder. Thus, a revision of the acoustic Strouhal number charts is required for finned tubes of different types and arrangements.

scholarly journals HST Image Restoration

1992 ◽  
Vol 9 ◽  
pp. 493-495
Author(s):  
Michael R. Rosa
Keyword(s):  
Image Restoration ◽  
World Wide ◽  
Black Box ◽  
Resolving Power ◽  
Future Research ◽  
Combine Data ◽  
Point Spread ◽  
Spread Function ◽  
Pipe Line ◽  
Scientific Return

Experience gained in a world wide effort to exploit restoration methods in order to improve the scientific return from the degraded HST optics calms down fears that HST might have lost all of its spatial resolving power. However, the problems posed by the characteristics of the point spread function (PSF) and of the detectors are such that “black-box” image restoration in an automatic procedure during pipe-line calibration is not applicable. Results from restoration experiments show the directions for future research: On the practical side ways are required to properly estimate the complicated PSF, to objectively describe errors, to treat undersampling and non-linear detectors, and to gain factors in throughput for large amounts of data; innovative example are methods to combine data obtained with differing PSFs (ground – space, space – space) and sampling.

Global mode analysis of a pipe flow through a 1:2 axisymmetric sudden expansion

2010 ◽  
Vol 22 (7) ◽  
pp. 071702 ◽  
Author(s):  
E. Sanmiguel-Rojas ◽  
C. del Pino ◽  
C. Gutiérrez-Montes
Keyword(s):  
Pipe Flow ◽  
Mode Analysis ◽  
Sudden Expansion ◽  
Global Mode ◽  
Flow Through

Flow Excited Acoustic Resonance of Two Side-by-Side Cylinders in Cross Flow

2006 ◽  
Author(s):  
Ronald Hanson ◽  
Atef Mohany ◽  
Samir Ziada
Keyword(s):  
Flow Regime ◽  
Strouhal Number ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Resonance Mechanism ◽  
Flow Phenomenon ◽  
Stable Flow ◽  
Center Distance

The aeroacoustic response of two side-by-side cylinders in cross-flow is investigated experimentally. In order to investigate the effect of the gap between the cylinders on the acoustic resonance mechanism, six spacing ratios between the cylinders have been investigated. These spacing ratios are in the range of T/D = 1.25 to 3, where D is the diameter of the cylinders and T is the center-to-center distance between them. Special attention is given to the bi-stable flow regime, which is reported in the literature for intermediate spacing ratios. During the tests, the acoustic cross-modes of the duct housing the cylinders are self-excited. For the intermediate spacing ratios, T/D = 1.25, 1.35, 1.46 and 1.75, two distinct vortex shedding frequencies at the off-resonance conditions are observed. These are associated with the wider and narrower wakes of the cylinders, as described in the literature. In this case, acoustic resonance occurs at a Strouhal number that is between those observed before the onset of resonance. In addition, the acoustic resonance synchronizes vortex shedding in the two wakes and thereby eliminates the bi-stable flow phenomenon. For large spacing ratios, T/D = 2.5 and 3, vortex shedding occurs at a single Strouhal number at which the acoustic resonance is initiated.

scholarly journals Pre-Sinkhole Seismicity at the Napoleonville Salt Dome: Implications for Local Seismic Monitoring of Underground Caverns

2020 ◽  
Vol 91 (3) ◽  
pp. 1672-1678
Author(s):  
Sean R. Ford ◽  
Douglas S. Dreger
Keyword(s):  
Acoustic Resonance ◽  
Salt Dome ◽  
Seismicity Rate ◽  
Unsteady Fluid Flow ◽  
Underground Caverns ◽  
Power Detector ◽  
Term Energy ◽  
Flow Through ◽  
Unsteady Fluid

Abstract The formation of a sinkhole at the Napoleonville salt dome located near Bayou Corne in Assumption Parish, Louisiana, was preceded by an increase in seismicity, as observed 10 km away by a continuously recording broadband seismic sensor. The seismicity rate in the days prior to the sinkhole formation contained hundreds of long-period events, some of which could be detected using a power detector (short-term to long-term energy ratio) tuned to the duration and frequency content of the seismicity. A characteristic of some of these events is a resonance near 0.4 Hz, which could be due to either an acoustic resonance within the brine-filled cavity or possibly due to unsteady fluid flow through a crack. A more exhaustive catalog was obtained using some of the events detected by the power detector as templates in a correlation detector. The full pre-sinkhole sequence of detections could offer lessons in remote monitoring of underground caverns.

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