Andreas Holmberg

Experimental determination of the aero-acoustic properties of an in-duct flexible plate

The potential reduction of the aeroacoustic noise generated by an in duct plate, byallowing it to be flexible, is studied experimentally. The test object is a triangular plateinserted at an angle i ...

The error suppression of an experimental over-determination of in-duct flow noise sources

The full aeroacoustic two-port measurement procedure in flow ducts involves the determination of a scattering matrix and a source term. In this paper, the improved error suppression of a recently d ...

Aeroacoustics of rectangular T-junctions subject to combined grazing and bias flows - An experimental investigation

Experimentally determined scattering matrices are used to study the low-amplitude interaction between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. Common for all flow combinations is that waves incident on the junction at the downstream side are only attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in-flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T junctions of circular ducts, the interaction is stronger for rectangular duct junctions.

Adaptive stabilized finite element framework for simulation of vocal fold turbulent fluid-structure interaction

As a step toward building a more complete model of voice production mechanics, we assess the feasibility of a fluid-structure simulation of the vocal fold mechanics in the Unicorn incompressible Unified Continuum framework. The Unicorn framework consists of conservation equations for mass and momentum, a phase function selecting solid or fluid constitutive laws, a convection equation for the phase function and moving mesh methods for tracking the interface, and discretization through an adaptive stabilized finite element method. The framework has been validated for turbulent flow for both low and high Reynolds numbers and has the following features: implicit turbulence modeling (turbulent dissipation only occurs through numerical stabilization), goal-oriented mesh adaptivity, strong, implicit fluid-structure coupling and good scaling on massively parallel computers. We have applied the framework for turbulent fluid-structure interaction simulation of vocal folds, and present initial results. Acoustic quantities have been extracted from the framework in the setting of an investigation of a configuration approximating an exhaust system with turbulent flow around a flexible triangular steel plate in a circular duct. We present some results of the investigation as well as results of the framework applied to other problems.

A test rig and experimental procedure to determine the aero- acoustic properties of a splitter plate

A test rig for a study of aero-acoustic phenomena over a sharp edge inside a duct is developed and described. The aero-acoustic losses over the edge are experimentally determined in quiescent air by measurements of a three-port, from which a power balance analysis yields the dissipated acoustic energy. The phenomenon of interest is interaction between the vortices shed by an acoustic wave propagating over a sharp edge and the wave itself. However, this phenomenon require high levels of particle velocity. The levels achieved are low, thus the dominating losses seen in the results are instead due to transfer of acoustic energy from sound waves into vibration energy in the splitter plate. This fact was observed by calculating the two-port scattering matrix over each sidebranch.