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EHTC 2011
.Simulation of nasal flow
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Development of a process for estimating the pressure drop
W.Liu, U.JanoskeLehrstuhl Stromungsmechanik, Bergische Universitat Wuppertal
B.Schmalenbeck, S.Langenberg, KWG EichhornHals-Nasen-Ohrenheilkunde/Chirurgie, Bonn
S.WenischInstitut fur Veterinar-Anatomie, Histologie und Embryologie, Giessen
November 7, 2011, Bonn
EHTC 2011 Simulation of nasal flow
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Layout
...1 Motivation
...2 Experiment
...3 Geometry modification
...4 Grid generation
...5 Simulation in OpenFOAM
...6 Results analysis
...7 Conclusion
EHTC 2011 Simulation of nasal flow
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Motivation
The Rhinomanometry is a preoperative investigation in orderto test the patency of the patient’s nose.
Project idea: develop methods to determine pressure drop inAnalytical solution and CFD simulation.
EHTC 2011 Simulation of nasal flow
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Motivation
The Rhinomanometry is a preoperative investigation in orderto test the patency of the patient’s nose.
Project idea: develop methods to determine pressure drop inAnalytical solution and CFD simulation.
EHTC 2011 Simulation of nasal flow
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Motivation
Figure: Project scheme
EHTC 2011 Simulation of nasal flow
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Experiment-Rhinomanometry
Figure: Rhinomanometry
EHTC 2011 Simulation of nasal flow
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Analytical solution
Figure: Flow channel partitioning
EHTC 2011 Simulation of nasal flow
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Analytical solution
Figure: Process of analytical solution
EHTC 2011 Simulation of nasal flow
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Analytical solution
The cross section planes are located by given points andnormal directions.
These sections have different lengths, bending angles, in-,andoutlet areas.
Figure: Parameters of sections
EHTC 2011 Simulation of nasal flow
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Analytical solution
Assumptions
Incompressible,isothermal flow ⇒ air density, viscosity andtemperature constant;
Average velocity of a section⇒ va = (vin + vout)/2;
Average hydraulic diameter⇒ da = (din + dout)/2;
Figure: Simplified model of the nose
EHTC 2011 Simulation of nasal flow
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Analytical solution
.The pressure drop of one section of the nose is calculated by:..
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∆p = λl
d
ρ
2c2 + ξ
ρ
2c2 + ξb
ρ
2c2
Pressure drop due to friction;
Change of the geometry sections;
Change of the curvature.
EHTC 2011 Simulation of nasal flow
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Analytical solution
Parameters of the equation
P—wetted perimeter of cross section,
d—hydraulic diameter, calculated by
d =4A
P
The section length l , perimeter of cross section P , and thecross sectional area A can be directly measured.
EHTC 2011 Simulation of nasal flow
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Analytical solutionParallel channels
Figure: Parallel channels
Q1 = Q(1− 1
1 +√
λ2λ1(d1d2 )
5)
EHTC 2011 Simulation of nasal flow
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Analytical solution
Implementation in ExcelThe total pressure drop is the summation of all sections.
∆ptotal =i=n∑i=1
∆pi
Therefore an Excel sheet is implemented regarding each section:
Figure: Excel sheet
EHTC 2011 Simulation of nasal flow
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Analytical solution
Results: Pressure drop with increasing volume flowThe curve of pressure over volume flow can be plotted based on
the results of the excel sheet.
Figure: Pressure drop/Volume flow diagram
EHTC 2011 Simulation of nasal flow
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Analytical solution
Results: Pressure drops in each section
Figure: Division of the flow channel Figure: Histogram of pressure drop
EHTC 2011 Simulation of nasal flow
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CFD process
Figure: CFD process
EHTC 2011 Simulation of nasal flow
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Geometry modification
Figure: HyperMesh
EHTC 2011 Simulation of nasal flow
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Geometry modification
Figure: Original STL model Figure: Modified model with a mask
EHTC 2011 Simulation of nasal flow
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Grid generation
3-D mesh generation
The snappyHexMesh utility generates 3-dimensional meshescontaining hexahedra cells.
Figure: 3-D mesh, 1.5M cells
EHTC 2011 Simulation of nasal flow
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Simulation Model
Figure: Simple boundary conditions
Assumptions:
steady state
isothermal
EHTC 2011 Simulation of nasal flow
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Simulation in OpenFOAM
Results:Pressure drop with increasing volume flowIn CFD simulation also show that the pressure drop increases
monotonically with volume flow.
Figure: Pressure drop/Volume flow diagram
EHTC 2011 Simulation of nasal flow
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Simulation in OpenFOAM
Visualization application: ParaView
The CFD simulation result are visualized in ParaView:
Figure: Pressure distribution (0.927 l/s, left side)
EHTC 2011 Simulation of nasal flow
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Result analysis
The different results are as follows:
Left side Right side
Volume flow [l/s] For all cases 0.982 0.927
Pressure [Pa]Experimental results 150 150Analytical results 1800 393
CFD simulation results 1585 229
Table: Comparison of different results
EHTC 2011 Simulation of nasal flow
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Result analysis
The analytical results differ from the experimental results mighthave the following reasons:
simplified model ⇐⇒ complex original geometry
low accuracy when setting assumptions and determinecoefficients
As to the CFD simulation results,Patched up model differ from the original geometry:
all holes closed ⇐⇒ leakage in experiment
unnecessary parts cut ⇐⇒ air might flow into these partsduring experiment
EHTC 2011 Simulation of nasal flow
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ConclusionThis study presents the attempt in analytical method andCFD solution against experiment. Possible further studywould be to get a complete model and make less modification.
snappyHexMesh and HyperMesh are both able to generatemeshes for complex geometries with small effort.
The simulation results depend on the boundary conditions,mesh quality etc.
Further models should be tested, work is still under progress,further projects are planned.
EHTC 2011 Simulation of nasal flow
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Thanks for your attention!
Questions?
EHTC 2011 Simulation of nasal flow
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