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Effect of Cross-Sectional Area Discontinuities in Closed Hard-Walled Ducts on Frequency of Longitudinal Modes

Meissner M.

Archives of Acoustics

2010

Vol. 35, No. 3

421-435

A simple analytical method is developed to estimate frequencies of longitudinal modes in closed hard-walled ducts with discontinuities in a cross-sectional area. The approach adopted is based on a general expression for the acoustic impedance for a plane wave motion in a duct and conditions of impedance continuity at duct discontinuities. Formulae for mode frequencies in a form of transcendental equations were found for one, two and three discontinuities in a duct cross-section. An accuracy of the method was checked by a comparison of analytic predictions with calculation data obtained by use of numerical implementation based on the forced oscillator method with a finite difference algorithm.

Wpływ struktury pól prędkości za skokowym zwężeniem rury na wartości współczynników oporów miejscowych

Strzelecka K., Jeżowiecka-Kabsch K.

Systems : journal of transdisciplinary systems science

2008

Vol. 13, spec. iss. 2/2

155--163

Real values of local loss coefficients for flow through pipe sudden contraction (contraction ratio d/D € (035, 0,82) were determined. Variations (in time and vicinity of resistance) and the influence of the Reynolds anmber (Re € (1000, 50000)) on phenomena in the vicinity of sudden contraction were taken into account. Experimental values of ζ coefficients were referred to flow structure in the vicinity of sudden contraction researches. It was pointed out that (for the Reynolds number Re d > Re gr - corresponding to orderly structure of velocity field) obtained ζ coefficient values are lower than those used in engineering calculations.