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Resonant absorbers
Published in Trevor J. Cox, Peter D'Antonio, Acoustic Absorbers and Diffusers, 2016
Trevor J. Cox, Peter D'Antonio
The last term in the equation is due to the boundary layer effect, and v = 15 × 10−6 m2s−1 is the kinemetric viscosity of air. This last term is often not significant unless the hole size is small, say, submillimetre in diameter. δ is the end correction factor, which, to a first approximation, is usually taken as 0.85 and derived by considering the radiation impedance of a baffled piston. A value of 0.85 does not, however, allow for the influence of neighbouring orifices because it is based on a calculation for a single piston. Consequently, other more accurate formulations exist and are summarised in Table 7.1.
Muffling Devices
Published in David A. Bies, Colin H. Hansen, Carl Q. Howard, Engineering Noise Control, 2018
David A. Bies, Colin H. Hansen, Carl Q. Howard
As ξ tends to zero, the value of the end correction tends to the value for a piston in an infinite baffle, as may be inferred from the discussion in Section 4.6. When there is flow of Mach number, M, either through or past the hole, the end correction ℓ0 must be multiplied by (1 − M)2. End corrections for quarter-wavelength tubes (QWTs) and Helmholtz resonators are discussed in Section 8.8.2.1.
Sound absorption and sound absorbers
Published in Heinrich Kuttruff, Room Acoustics, 2016
The correction 2Δb, called ‘end correction’, accounts for the fact that the streamlines (see Figure 6.2b) cannot contract or expand abruptly but only gradually before entering or after leaving an aperture. For a circular aperture with radius a, the end correction is Δb=π4a
Active Control of Combustion Noise by a Twin Resonator Trim Adjustment System
Published in Combustion Science and Technology, 2022
Varghese M. Thannickal, T. John Tharakan, Satyanarayanan R. Chakravarthy
Here, δ = 8d/3π is the end correction, ν is the kinematic viscosity of the combustor gases, ω is the angular frequency of the combustion noise, c is the speed of sound, l is the length of the resonator neck, d is the diameter of the resonator neck and is the length of the cavity. ω, in turn, is a function of the operating conditions and geometry of the chamber. The mean flow through the orifice and the combustor has been neglected.