Aeroacoustic response of an array of tubes with and without bias-flow

Abstract

Heat exchangers, consisting of tube arrays in a cross-flow are a vital component of power generation systems. They are of interest from an acoustic point of view, because they can reflect, transmit and absorb an incident sound wave; in other words, they have the potential to act as a sound absorber and even as a passive control device to prevent a thermoacoustic instability in the power generation system. This paper presents a fundamental study of the aeroacoustic response of a tube array with and without bias-flow (also called crossflow). The study has a theoretical and an experimental side. On the theoretical side, a new model, based on the assumption of quasi-steady flow, was developed to predict the acoustic reflection and transmission coefficient of a tube array with bias-flow. Also, the model by Huang and Heckl (Huang and Heckl, 1993, Acustica 78, 191-200) for the case without bias-flow was evaluated. On the experimental side, flow-duct experiments using a multi-microphone technique were performed to validate the predictions from both models. The agreement was found to be very good for low frequencies. The measurements revealed the limit of validity of the quasi-steady model in terms of the Strouhal number. Although this limit is quite low, our quasi-steady model can serve as a valuable tool for designers of heat exchangers.

Advances by the Marie Curie project TANGO in thermoacoustics

“…-The acoustic wavelength is large enough so that the 2D flow region can be regarded as compact, Figure 43. Schematic of two half-cylinders in a flow duct (from Figure 4 in Surendran et al 86 ).…”

“…The flow separation location is required to determine the height of the jet. This is found by solving the von Ka´rma´n equations with the Thwaites method (see Appendix A in Surendran et al 86 ). The jet height depends on the following parameters: diameter and spacing of the cylinders, upstream Mach number, and on the viscosity and density of the fluid.…”

“…A multi-microphone technique was used to measure the transmission and reflection coefficients at three frequencies (f ¼ 150, 250, 350 Hz). Further experimental details are given in Surendran et al 86 In order to answer question (1), the dependence of the coefficients on the Strouhal number was measured. As expected, there was good agreement between the theoretical and experimental results at low Strouhal numbers, but the agreement started to break down if St 4 0:16.…”

“…This transfer function was determined in two independent studies by Surendran et al 89,90 and Strobio Chen et al 91 Both used a CFD solver to calculate heat transfer rate (integrated over the surface of the HEX) in response to an imposed velocity perturbation. This was Fourier-transformed into the frequency domain, and the HEX transfer function was then calculated from (85).…”

“…The transfer function for the HEX (see equation (85)) is defined for a 1D velocity field. By introducing the velocity average over a cross-section at a chosen location between the flame and the HEX, Hosseini et al 94 extended the definition to non-uniform velocity fields.…”