Measurement of pulsatile flow characteristics in interaction with rigid and flexible wall
Title Alternative:Research report GACČR nr. 17-19444S Interaction of heterogeneous liquid with flexible wall
Loading...
Date
Journal Title
Journal ISSN
Volume Title
Publisher
Technická univerzita v Liberci
Abstract
Pulse flow was generated by a membrane pump. The nature of the pulsatile flow was measured
with pressure sensors. We got information on the pressure development inside the circuit. Each
phase of the pulse was evenly divided into 10 equal time slots. The individual slots were
synchronized to the initial pressure change at 0.14Bar. The evaluation of the pressure
measurement has already revealed the backward effect of the flexible wall. Especially when
compared to glass rigid wall. Differences in pressures course are mostly significant in the peak
width and lower stabilised pressure value. The flexible material absorbs part of pressure and
expands its diameter.
The liquid flow can be divided into four regimes: The first regime corresponds to pressure
increase. The liquid flow is accelerated. The maximal fluid velocities reach 440 mm/s (Re 8800).
The second regime is the highest point of pressure increase, where physically occurs the
maximum membrane inclination, and closure of the pumps valves. At this point, the fluid
stagnates, resulting in slowing down of the flow rate to 70 mm/s (Re 1400), and changing the characteristic velocity profile. This regime can be said as transient mode. The velocity profile is
characterized with typical velocity decrease in the middle of cross section. This effect was found
for both measurements – using rigid and flexible wall.
The other phase of liquid acceleration can be observed in the third regime. Here, the liquid is fed
with the pump. This acceleration last during the pressure decrease. This regime is characteristic
with turbulent profile shape, and maximal flow velocity reach 260 mm/s (Re 5200). The fourth
regime is observed since 6/5π period, when the pressure drop and starts to be stabilized. Here
we can observe the liquid flow slowdown that is close to laminar profile shape. The maximal
velocities in this regime are 35 mm/s (Re 700).
There is an oscillation of a pressure, which leads to the formation of vortex structures near the
wall. These structures are highlighted by the elasticity of the wall. The vortex structures were
analysed using Proper Orthogonal Decomposition (POD). The most significant modes are for
transient part of fluid flow and turbulent zone. The first 20 decomposition modes can be said as
dominant. Here can be found vortex structures with kinetic energy of 10%. The nonstationary
backward vortexes are developed close to the wall, as the fluid flow velocity is very small. The
prevailing dominant effect on the fluid flow comes from the released kinetic energy from the
relaxing flexible walls, especially in the fourth regime of pressure course. This effect is not
significant for rigid walls.
There were set an experimental setup for studying of cavitation base on Ventury tube. The fluid
flow was analysed using high speed visualization methods in two interrogation areas in crosssection. The region of interest was focused on the swirling cavitation structure. The experiments
run in 2018 were run in rigid wall. The fluid was also seeded with fluorescent particles for PIV
measurement so the simple visualization was filled with fluid motion data’s. The investigated
area was observed with synchronized two cameras recording parallel. The set of images were
processed using supressing and dewarping algorithms. The experimental setup is prepared for
the measurement on flexible wall and pulsatile flow.
Description
Subject(s)
flexible wall, luid flow, heterogeneous liquid, particle image velocimetry, pulsatile flow, rigid wall