DOMINANT CONTRIBUTION OF DIPOLES IN THE TURBULENCE-GENERATED NOISE

Abstract

A problem of noise generation by a compact region of turbulence in an infinite straight immovable rigid-walled pipe of circular cross-section is solved by the Green’s function technique and the normal mode method. A turbulence region is modeled by quadrupoles and dipoles. The cases of homogeneous and non-homogeneous turbulence are considered. The generated noise power is shown to be a sum of powers of the pipe acoustic modes. The acoustic mode power consists of the three parts. The first part is the power generated by the quadrupoles, the second one results from the dipoles, and the third one is due to interaction of the quadrupoles and dipoles. Also, a particular case of the problem is considered. In this case the situation is studied when the generated noise field is dominated by the contribution made by surface dipoles. Those flows and shapes of the local pipe narrowing are of concern, that result in large or small eddies distributed uniformly in the turbulence region behind the narrowing. The corresponding simplified expressions for the generated noise power are obtained in the considered cases. Also, estimates of these expressions are carried out for the characteristic scales in the turbulence region.

ых диполей. При этом интерес представляют такие потоки и формы локальных сужений труб, при которых регион турбулизированного сужением течения занимают равномерно распределенные большие или малые вихри.  Для этих случаев получены соответствующие упрощенные выражения для мощности сгенерированного шума и проведены их оценки для характерных масштабов в области турбулентности.