Simulation of nasal. flow...

Transcription

1 Simulation of nasal flow Development of a process for estimating the pressure drop W.Liu, U.Janoske Lehrstuhl Strömungsmechanik, Bergische Universität Wuppertal B.Schmalenbeck, S.Langenberg, KWG Eichhorn Hals-Nasen-Ohrenheilkunde/Chirurgie, Bonn S.Wenisch Institut für Veterinär-Anatomie, Histologie und Embryologie, Giessen November 7, 2011, Bonn..

2 Layout.1. Motivation.2. Experiment.3. Geometry modification.4. Grid generation.5. Simulation in OpenFOAM.6. Results analysis.7. Conclusion..

3 Motivation The Rhinomanometry is a preoperative investigation in order to test the patency of the patient s nose. Project idea: develop methods to determine pressure drop in Analytical solution and CFD simulation...

4 Motivation The Rhinomanometry is a preoperative investigation in order to test the patency of the patient s nose. Project idea: develop methods to determine pressure drop in Analytical solution and CFD simulation...

5 Motivation Figure: Project scheme..

6 Experiment-Rhinomanometry Figure: Rhinomanometry..

7 Analytical solution Figure: Flow channel partitioning..

8 Analytical solution Figure: Process of analytical solution..

9 Analytical solution The cross section planes are located by given points and normal directions. These sections have different lengths, bending angles, in-,and outlet areas. Figure: Parameters of sections..

10 Analytical solution Assumptions Incompressible,isothermal flow air density, viscosity and temperature constant; Average velocity of a section v a = (v in + v out )/2; Average hydraulic diameter d a = (d in + d out )/2; Figure: Simplified model of the nose..

11 Analytical solution. The pressure drop of one section of the nose is calculated by:..... p = λ l d Pressure drop due to friction; Change of the geometry sections; Change of the curvature. ρ 2 c2 + ξ ρ ρ 2 c2 + ξ b 2 c2..

12 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 the cross sectional area A can be directly measured...

13 Analytical solution Parallel channels Figure: Parallel channels 1 Q 1 = Q(1 ) 1 + λ2 λ 1 ( d 1 d 2 ) 5..

14 Analytical solution Implementation in Excel The total pressure drop is the summation of all sections. i=n p total = p i Therefore an Excel sheet is implemented regarding each section: i=1 Figure: Excel sheet..

15 Analytical solution Results: Pressure drop with increasing volume flow The curve of pressure over volume flow can be plotted based on the results of the excel sheet. Figure: Pressure drop/volume flow diagram..

16 Analytical solution Results: Pressure drops in each section Figure: Division of the flow channel Figure: Histogram of pressure drop..

17 CFD process Figure: CFD process..

18 Geometry modification Figure: HyperMesh..

19 Geometry modification Figure: Original STL model Figure: Modified model with a mask..

20 Grid generation 3-D mesh generation The snappyhexmesh utility generates 3-dimensional meshes containing hexahedra cells. Figure: 3-D mesh, 1.5M cells..

21 Simulation Model Assumptions: steady state isothermal Figure: Simple boundary conditions..

22 Simulation in OpenFOAM Results:Pressure drop with increasing volume flow In CFD simulation also show that the pressure drop increases monotonically with volume flow. Figure: Pressure drop/volume flow diagram..

23 Simulation in OpenFOAM Visualization application: ParaView The CFD simulation result are visualized in ParaView: Figure: Pressure distribution (0.927 l/s, left side)..

24 Result analysis The different results are as follows: Left side Right side Volume flow [l/s] For all cases Experimental results Pressure [Pa] Analytical results CFD simulation results Table: Comparison of different results..

25 Result analysis The analytical results differ from the experimental results might have the following reasons: simplified model complex original geometry low accuracy when setting assumptions and determine coefficients 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 parts during experiment..

26 Conclusion This study presents the attempt in analytical method and CFD solution against experiment. Possible further study would be to get a complete model and make less modification. snappyhexmesh and HyperMesh are both able to generate meshes 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...

27 Thanks for your attention! Questions?..