Numerical Prediction of the Phase Difference in Tube Bundles Experiencing Streamwise Fluidelastic Instability

Recent experimental investigations have shown that tube arrays can become unstable in the streamwise direction. This is contrary to the long-held notion that fluidelastic instability is only a concern in the direction transverse to the flow. The possibility of streamwise fluidelastic instability (FEI) as a potential threat to the integrity of tube bundles was confirmed by the recent failures of newly installed replacement steam generators. A number of investigations were conducted to uncover the nature of this mechanism. A theoretical framework was developed by Hassan and Weaver [1] to model streamwise fluidelastic instability in a bundle of flexible tubes. The model utilized a simple time lag expression for the flow channel area perturbation. The current work aims at developing a numerical model to precisely predict the flow perturbation characteristics in a tube bundle due to streamwise tube motion. Flow simulations were carried out for single phase fluid flow in a parallel triangle tube bundle array with 1.2, 1.5 and 1.7 pitch to diameter ratios. The numerical model was benchmarked against numerical and experimental results available in the FEI literature. Simulations were carried out for a range of reduced flow velocities. The model results showed that the upstream flow perturbation magnitude and phase are different from those obtained in the downstream of the moving tube. The obtained flow perturbation characteristics were implemented in the Hassan and Weaver [1] model and the streamwise FEI threshold was predicted.

Aerial Mapping of Odorous Gases in a Wastewater Treatment Plant Using a Small Drone

Wastewater treatment plants (WWTPs) are sources of greenhouse gases, hazardous air pollutants and offensive odors. These emissions can have negative repercussions in and around the plant, degrading the quality of life of surrounding neighborhoods, damaging the environment, and reducing employee’s overall job satisfaction. Current monitoring methodologies based on fixed gas detectors and sporadic olfactometric measurements (human panels) do not allow for an accurate spatial representation of such emissions. In this paper we use a small drone equipped with an array of electrochemical and metal oxide (MOX) sensors for mapping odorous gases in a mid-sized WWTP. An innovative sampling system based on two (10 m long) flexible tubes hanging from the drone allowed near-source sampling from a safe distance with negligible influence from the downwash of the drone’s propellers. The proposed platform is very convenient for monitoring hard-to-reach emission sources, such as the plant’s deodorization chimney, which turned out to be responsible for the strongest odor emissions. The geo-localized measurements visualized in the form of a two-dimensional (2D) gas concentration map revealed the main emission hotspots where abatement solutions were needed. A principal component analysis (PCA) of the multivariate sensor signals suggests that the proposed system can also be used to trace which emission source is responsible for a certain measurement.

The analysis of dynamics of periodic fluid-loaded flexible tubes

In this report, we consider a periodic tube consisting of absolutely rigid sections alternated with soft segments of the same inner diameter under the action of a tensile force. The purpose of this analysis is to explore possibilities to suppress wave propagation using this complex tube model as a muffler. Its waveguide properties are assessed by means of a mathematical model formulated in the framework of Floquet theory and the results are compared with the eigenfrequency and eigenmode analysis of a unit symmetric periodicity cell. The setup consisting of these alternating sections creates the stop band effect, so that it may be called a ‘macroscale acoustic metamaterial’.

FSI Computation and Experimental Verification of Fluid Flow in Flexible Tubes

Presented paper is focused on the experimental and computational study of fluid flow in pipes with flexible walls. One possible real example of this phenomenon is the blood flow in arteries or their substitutes in the human body. The artery material itself should be understood as anisotropic and heterogeneous. Therefore, the experiment was carried out on the deforming tube, made of silicone (polydimethylsiloxane - PDMS). Obtained results and observed events were verified by numerical FSI simulations. Due to the large deformations occurring during loading of the tube, it was necessary to work with a dynamic mesh in the CFD part. Based on experimental testing of the tube material, a non-Hookean and Mooney-Rivlin material model were considered. Blood flowing in vessels is a heterogeneous liquid and exhibits non-Newtonian properties. In the real experimental stand has been somewhat simplified. Water, chosen as the liquid, belongs to the Newtonian liquids. The results show mainly comparisons of unsteady velocity profiles between the experiment and the numerical model.