Second Paper: Lateral Helmholtz Resonator Silencer with Turbulence Absorption

1967 ◽  
Vol 182 (1) ◽  
pp. 60-72 ◽  
Author(s):  
Y. N. Chen
Keyword(s):  
Pipe Flow ◽  
Helmholtz Resonator ◽  
High Flow ◽  
Exhaust Pipe ◽  
Helmholtz Resonators ◽  
Intense Noise ◽  
Lateral Resonance ◽  
Fast Flow ◽  
High Level ◽  
Flow Velocities

Lateral Helmholtz resonators are ineffective for fast flow because of the turbulence caused by the movement of the gas mass from the resonator neck into the main pipe flow. The absorption of this turbulence at its source is an effective method for keeping the resonator silencing ability at a high level. Experimental results on an acoustic filter formed by resonators for flow velocities up to 80 m/s, so treated, are compared with the theory. There is evidence of lateral resonance of the gas column in the exhaust pipe at high flow velocities, detected as an intense noise of a discrete frequency (1000 Hz). The excitation of this resonance was found to be due to the pseudo-acoustic wave caused by the neck jets in the resonator. The influence of the flow upon the natural frequency of the resonator is also discussed. The Reynolds number of the flow seems to play an essential role on this point.

Development of an Adaptive Helmholtz Resonator for Broadband Noise Control

2004 ◽  
Author(s):  
Simon J. Este`ve ◽  
Marty E. Johnson
Keyword(s):  
Helmholtz Resonator ◽  
Broadband Noise ◽  
Experimental Result ◽  
Helmholtz Resonators ◽  
Large Cylinder ◽  
Payload Fairing ◽  
Compact Design ◽  
High Level ◽  
Design Options ◽  
Control Application

This paper presents the development of adaptive Helmholtz resonators aimed at controlling broadband disturbance for the reduction of noise transmission into rocket payload fairing. Helmholtz resonators are commonly used for narrow band control application and so are designed to present the lowest amount of damping yielding maximum impedance. For this particular application however, optimal damping ratios usually superior to 4% are required. This relatively high level of damping permits more lightweight and compact design options to be considered that are not possible for low damping applications. Two design solutions are presented. The first tunes the resonator by varying the length of an accordion neck. The second varies the HR opening using an iris diaphragm. The characteristics of these two devices are measured, and a solution to maintain the damping level relatively constant is also proposed. Finally, experimental result obtained in a large cylinder representative of a payload fairing using 8 adaptive resonators is presented.

scholarly journals The Debris Content of Surging Glaciers in Svalbard and Iceland

1975 ◽  
Vol 14 (72) ◽  
pp. 395-406 ◽  
Author(s):  
Chalmers M. Clapperton
Keyword(s):  
Bottom Sediments ◽  
High Flow ◽  
Frictional Heat ◽  
Horizontal Extent ◽  
Compressive Flow ◽  
Melt Water ◽  
Terminal Zone ◽  
Trigger Zone ◽  
Vertical Development ◽  
Flow Velocities

In Svalbard and Iceland there appears to be much more debris entrained in glaciers that surge than in those which do not. Conditions particularly favourable for the basal incorporation of debris develop as a consequence of the high flow velocities attained by a surge. These are increased cavitation in the lee of obstacles and an increased supply of basal melt water resulting from frictional heat and from the trigger zone. Layers of regelation ice incorporating debris can thus develop to a much greater vertical and horizontal extent than in non-surging glaciers. Excessive shearing, and the distortion of foliation structures in the terminal zone of compressive flow, enhance the vertical development of the debris-rich regelation layers. Glaciers that surge over outwash and/or fjord-bottom sediments become particularly rich in debris.

Scour Around Bridge Piers at High Flow Velocities

1980 ◽  
Vol 106 (11) ◽  
pp. 1827-1842 ◽  
Author(s):  
Subhash C. Jain ◽  
Edward E. Fischer
Keyword(s):  
High Flow ◽  
Bridge Piers ◽  
Flow Velocities

Discussion of “Scour Around Bridge Piers at High Flow Velocities”

1981 ◽  
Vol 107 (7) ◽  
pp. 958-958
Author(s):  
Fred W. Blaisdell ◽  
Clayton L. Anderson
Keyword(s):  
High Flow ◽  
Bridge Piers ◽  
Flow Velocities

Numerical study for increasement of low frequency sound insulation of double-panel structure using sonic crystals with distributed Helmholtz resonators

2019 ◽  
Vol 33 (14) ◽  
pp. 1950138
Author(s):  
Myong-Jin Kim
Keyword(s):  
Free Space ◽  
Transmission Loss ◽  
Numerical Study ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Sound Insulation ◽  
The Finite Element Method ◽  
Helmholtz Resonators ◽  
Sonic Crystal ◽  
Sonic Crystals

Numerical simulations of the sound transmission loss (STL) of a double-panel structure (DPS) with sonic crystal (SC) comprised of distributed local resonators are presented. The Local Resonant Sonic Crystal (LRSC) consists of “C”-shaped Helmholtz resonator columns with different resonant frequencies. The finite element method is used to calculate the STL of such a DPS. First, the STLs of LRSC in free space and the DPS with LRSC are calculated and compared. It is shown that the sound insulations of the local resonators inserted in the double panel are higher than that in free space for the same size of the SCs and the same number of columns. Next, STL of the DPS in which the SC composed of three columns of local resonators having the same outer and inner diameters but different slot widths are calculated, and a reasonable arrangement order is determined. Finally, the soundproofing performances of DPS with distributed LRSC are compared with the case of insertion of general cylindrical SC for SC embedded in glass wool and not. The results show that the sound insulation of the DPS can be significantly improved in the low frequency range while reducing the total mass without increasing the thickness.

scholarly journals Surface Air Movement: An Important Contributor to Ventilation of Isolated Subsurface Structures?

2019 ◽  
Vol 4 (2) ◽  
pp. 23 ◽  
Author(s):  
Thomas Neil McManus ◽  
Assed Haddad
Keyword(s):  
Air Flow ◽  
Helmholtz Resonator ◽  
Worker Safety ◽  
Time Base ◽  
Near Surface ◽  
Helmholtz Resonators ◽  
Subsurface Structures ◽  
Air Movement ◽  
Air Speed ◽  
Almost All

This study reports on near-surface airspeed measured using a fast-responding thermoanemometer during an investigation of ventilation of an isolated subsurface structure induced by natural forces. Air speed changes continuously, rapidly, and unpredictably when assessed on the time base of one or two seconds. Zero, the most common air speed, occurred in almost all tests throughout the year but especially during cool and cold months. The most probable non-zero air speed, 10.7 m/min (35 ft/min), occurred in all tests. This air speed is below the level of detection by the senses. The number of zero values and the height of the peak at 10.7 m/min follow a repetitive annual cycle. Isolated subsurface structures containing manhole covers share the characteristics of Helmholtz resonators. Grazing air flow across the opening to the exterior induces rotational air flow in the airspace of a Helmholtz resonator. Rotational flow in the airspace potentially influences the exchange of the confined atmosphere with the external one. Ventilation of the airspace occurs continuously and without cost and is potentially enhanced by the unique characteristics of the Helmholtz resonator excited by surface air movement. These results have immense importance and immediate applicability to worker safety.

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