Simulation Study on Characteristics of the Vortex Structure in Human Mouth-throat Model in Cyclic Respiratory Pattern

Transcription

1 Avalable onlne at Energy Proceda 17 (2012 ) Internatonal Conference on Future Electrcal Power and Energy Systems Smulaton Study on Characterstcs of the Vortex Structure n Human Mouth-throat Model n Cyclc Respratory Pattern SUN Dong,XU Xn-X*,ZHAO Xu-Guo,Tan Shu-Ln,L Fu-Sheng Insttute of Medcal Equpment, Academy of Mltary Medcne Scences; Natonal Bologcal Protecton Engneerng Center, Tann Abstract The research on vortex structure and vortex evoluton n human upper respratory tract can deepen understandng of the characterstcs of the arflow n human upper respratory tract and plays a very mportant role n analyzng the dffuson, transton and deposton patterns of aerosol n human upper respratory tract. Large eddy smulaton was used to smulate the vortex structure and vortex movement n human mouth-throat model n cyclc respratory pattern, and the vortex structure and vortex evoluton n mouth-throat model was dscussed. The results show that et formatons n pharynx and laryngeal lead to two vortcty growth regons at cyclc nhalaton flow, flat vortex appeared n the throat, a curved vortex lke the trachea wall appeared n the anteror wall of trachea, and nearly symmetrc reverse vortex pars appeared n the trachea; a vortex lke 3 appeared n the posteror wall of the throat, two curved vortexes lke eyebrow appeared n the posteror wall of the pharynx Publshed by by Elsever Ltd. Ltd. Selecton and/or and/or peer-revew under under responsblty of Hanan of [name Unversty. organzer] Open access under CC BY-NC-ND lcense. Key wordscyclc respratory patternmouth-throat model vortex structure vortex evolutonlarge eddy smulaton 1.Introducton The arflow n human mouth-throat leads to the generaton of varous scales vortexes and the cyclc varaton of pressure and sharng stress, whch wll affect the dffuson and deposton of aerosol. Wth the effects of respratory mode and geometrcal characterstcs of respratory tract, a transton from lamnar flow to turbulence occurs n respratory tract. In ths transton, complex arflow movements appears, such as the vortex structure [1], the flow separaton [2] and the second flow [3], whch wll result n the dfferent dstrbuton of pressure [4] and sharng stress. In fact, ths process of transton also occurs n the dffuson of aerosol, whch essentally presented as the affectons of the vortex structures and the cyclc varaton of pressure and sharng stress on the dffuson of aerosol. Recent years, prelmnary studes on vortex flow have been conducted by many scholars, the whole moton state of vortex flow [256] has been analyzed, and that the structure of Publshed by Elsever Ltd. Selecton and/or peer-revew under responsblty of Hanan Unversty. Open access under CC BY-NC-ND lcense. do: /.egypro

2 SUN Dong et al. / Energy Proceda 17 ( 2012 ) human upper respratory tract and the respratory flow cause vortex flow has been proved [7]. However, there are few systematc studes on vortex structure and vortex evoluton n human upper respratory tract, whch has restrcted the understandng of arflow movement characterstc n human upper respratory tract. In ths paper, large eddy smulaton was used to smulate precse flow feld n human mouth-throat model n the condtons of the low ntensve cyclc respratory patterns. The process of vortex evoluton n human mouth-throat model was studed and the characterstcs of vortex structure n mouth-throat model at dfferent tme were dscussed. 2.Geometrcal model and mathematcal model 2.1. Geometrcal model As shown n Fg.1, an dealzed mouth-throat model geometry that s developed at Aerosol Research Laboratory of Alberta (ARLA) conssts of oral cavty, pharynx, larynx and trachea. The szes of the model are smlar to those gven by Aerosol Research Laboratory of Alberta (ARLA) [8] and Stapleton K.W [9]. 2.2.Governng equatons of the gas phase Fg. 1 Human mouth-throat model The large eddy smulaton used n the paper s a transton between drect numercal smulatons and theoretcal model smulatons. It has a great potental n engneerng applcaton and fundamental research, and s a present research focus on flud numercal smulaton. The governng equatons [10] of large eddy smulaton s obtaned from the N-S flterng equatons, and t s tensor expresson can be descrbed as: u 0 x u uu 1 p 2 u t x x x Where,, 1,2, 3, and,, u and p are flow densty, knetc molecular vscosty, large scale part of flow velocty and pressure, respectvely. And the Sub-grd scale stress : uu uu. Large eddy smulaton wth Smagornsky sub-grd scale model was used n the present work, and sub-grd scale stress can be descrbed as the followng:

3 1788 SUN Dong et al. / Energy Proceda 17 ( 2012 ) T S kk 3 Where s Kronecker symbol, and stran rate tensor S can be defned as: S u x Sub-grd eddy vscosty T can be descrbed as: ( ) Where u x 2 T C s S 2S S, and the Smagornsky constant C s =0.1 was adopted n ths paper. S 2.3.Numercal smulaton In the smulaton for flow feld n human mouth-throat model under the condtons of the low ntensve cyclc respratory patterns, the respratory flow changes accordng to the sne wave functon, as s shown n the Fg.2. The breathng ntensty Q=30L/mn, the respratory frequency s 15 cycle/mn. The assocated boundary condtons nclude unform velocty prescrbed at the mouth nlet and zero pressure at the outlets. Meanwhle, the arway condut s assumed to be smooth and rgd. The effects of arway condut flexblty were not consdered, and the no-slp boundary condton was adopted n the present analyss. 8 tme ponts (T 1 ~T 8 ) n a cycle were analyzed as the smulaton result, where T 1 =0.2 st 2 =0.5sT 3 =1s T 4 =1.5sT 5 =2.2sT 6 =2.5sT 7 =3sT 8 =3.5s, as s shown n the Fg Model valdaton Fg. 2 the change of respratory flow n cyclc respratory patterns The experment research was performed wth the Partcle mage velocmetry (PIV) technque and nspraton flows were examned under steady flow condtons wth the breathng ntensty Q=30L/mn. Comparson of averaged velocty magntude s performed between PIV measurement and large eddy smulaton result to verfy the accuracy of the numercal smulaton results. As the Fg.3 shows, the comparson of averaged velocty magntude between the expermental results [11] of the larynx and the numercal results has been dsplayed. The results show that the numercal smulaton data are n reasonable agreement wth expermental measurements, whch verfes that the large eddy smulaton methods are accurate and reasonable.

4 SUN Dong et al. / Energy Proceda 17 ( 2012 ) B A Fg.3 Comparson of arflow patterns between expermental results (A) and large eddy smulaton results (B) of the larynx 3.Results and dscusson 3.1.Evoluton of vortex structure n mouth -throat model n cyclc respratory pattern The vortcty dstrbuton contours n symmetrcal vertcal plane of human mouth-throat model and the so-surface of vortcy at dfferent tme were dsplayed respectvely n Fg.4 and Fg.5, and the evoluton process of vortex structure n human mouth-throat model n cyclc respratory pattern was revealed. In nspratory acceleraton phase, the arflow entered nto oral cavty through mouth, then arrved pharynx. Due to the sectonal area of pharynx decreased rapdly, the frst et generated n pharynx and two vortcty growth regons formed on the anteror and posteror wall of pharynx. When the arflow arrved larynx, the second et generated n larynx owng to the lmtaton of the secton of glotts, and a vortcty growth regon formed n the glotts. Wth the passage of tme, the vortcty of pharynx and glotts ncreased rapdly, the vortex structure moved to downstream of the arflow, and the core of vortex n the trachea was gradually nearng the anteror wall of trachea. At t=1s, the vortcty dstrbuton n human mouth-throat model present a knd of fully developed stuaton, and the vortcty n every part reached ts maxmum. As s shown n Fg.5, n nspratory acceleraton phase, the vortcty developed from pharynx and larynx, and a curved vortex lke the trachea wall appeared n the model. From the pcture at 1.5s, t can be drown that the vortcty decreased gradually n nspraton deceleraton phase, and the dstrbuton of vortcy at the fnshed tme approached to that at the ntal tme. a b c d e f Fg.4 The vortcty dstrbuton contours n symmetrcal vertcal plane of human mouth-throat model at dfferent tmeat=0.2s bt=1sct=1.5sdt=2.2set=3sft=3.5s

5 1790 SUN Dong et al. / Energy Proceda 17 ( 2012 ) Characterstcs of vortex structure n mouth-throat model at T=1s In Fg.6, the vortcty dstrbuton n dfferent cross sectons of the human mouth-throat model at t=1s were dsplayed. From the cross-sectons of A-A, t can be seen that as the arflow entered nto pharynx, the vortcty n boundary layer ncreased and a stuaton of hgher external and lower nternal vortcty was formed. As the arflow arrved cross-sectons of B-B, a et generated n pharynx and the vortex flow separated. Meanwhle, a flat vortex wth hgher central vortcty appeared n the throat. When the arflow got to glotts, a complex vortex structure of hgher vortcty on posteror wall and lower vortcty n the center generated owng to the lmtaton of the secton of glotts, as s shown n the cross-secton C-C. Due to the drecton of et fow s to the anteror wall of trachea, a phenomenon that vortcty extended to the anteror wall of trachea formed, and a curved vortex lke the trachea wall appeared n the anteror wall of trachea, as s shown n the cross-secton E-E. At the same tme, nearly symmetrc reverse vortex pars appeared n the trachea, whch was smlar to the kdney vortex and reverse kdney vortex appeared n the et flow of transverse vortex flow, as s shown n the cross-secton E-E and F-F. a b c d e f Fg.5 The so-surface of vortcy n human mouth-throat model at dfferent tmeat=0.2sbt=1sct=1.5sdt=2.2s et=3sft=3.5s 3.3.Characterstcs of vortex structure n mouth-throat model at T=3s In Fg.7, the vortcty dstrbuton n dfferent cross sectons of the human mouth-throat model at t=3s were dsplayed. From the cross-sectons of E-E and F-F, t can be seen that as the arflow entered nto trachea, the vortcty n boundary layer ncreased and a stuaton of hgher external and lower nternal vortcty was formed. As the arflow arrved cross-sectons of D-D, a et generated n glotts and two vortcty growth regons formed on the anteror and posteror wall of larynx. Due to the drecton of et fow s to the posteror wall of larynx, the vortcty extended to the posteror wall of larynx. A complex vortex structure of hgher vortcty on posteror wall and lower vortcty on anteror wall generated, and a vortex lke 3 appeared n the posteror wall of the throat, as s shown n cross-sectons of C-C. When the arflow reached pharynx, the second et generated n pharynx and two vortcty growth regons formed on the anteror and posteror wall of pharynx. Then, two curved vortexes lke eyebrow appeared n the posteror wall of the pharynx, as s shown n cross-sectons of B-B. After the flow reached mouth, the vortcty dspersed and varous scales of vortexes generated, as s shown n cross-sectons of A-A.

6 SUN Dong et al. / Energy Proceda 17 ( 2012 ) A-A Fg. 6 Vortcty dstrbuton n dfferent cross sectons of the human mouth-throat model at t=1s A-A Fg. 7 Vortcty dstrbuton n dfferent cross sectons of the human mouth-throat model at t=3s 4.Conclusons Large eddy smulaton was used to smulate the vortex structure and vortex movement n human mouth-throat model n the condtons of the low ntensve cyclc respratory patterns wth the breathng ntensty Q=30 L/mn and the vortex structure and vortex evoluton n mouth-throat model were dscussed. The followng concluson can be drawn: In nspratory acceleraton phase, two et formatons n pharynx and laryngeal lead to two vortcty growth regons at cyclc nhalaton flow. Wth the passage of tme, the vortcty of pharynx and glotts ncreased rapdly, the vortex structure moved to downstream of the arflow, and the core of vortex n the trachea was gradually nearng the anteror wall of trachea. In nspraton deceleraton phase, the vortcty decreased gradually and the dstrbuton of vortcy at the fnshed tme approached to that at the ntal tme. In expratory acceleraton phase, two et formatons n pharynx and glotts lead to two vortcty growth regons. Wth the passage of tme, the vortex structure moved to downstream of the arflow, the maxmum appeared on the posteror wall of pharynx. In expraton deceleraton phase, the vortcty decreased gradually and the dstrbuton of vortcy at the fnshed tme approached to that at the ntal tme. At t=1s, the vortcty dstrbuton n human mouth-throat model present a knd of fully developed stuaton. A flat vortex appeared n the pharynx, and a curved vortex lke the trachea

7 1792 SUN Dong et al. / Energy Proceda 17 ( 2012 ) wall appeared n the anteror wall of trachea. A nearly symmetrc reverse vortex pars appeared n the trachea, whch was smlar to the kdney vortex and reverse kdney vortex appeared n the et flow of transverse vortex flow. At t=1s, the vortcty dstrbuton n human mouth-throat model present a knd of fully developed stuaton. A vortex lke 3 appeared n the posteror wall of the throat, two curved vortexes lke eyebrow appeared n the posteror wall of the pharynx. After the flow reached mouth, the vortcty dspersed and varous scales of vortexes generated. References [1] Martn ANagelsJohn ECaterLarge eddy smulaton of hgh frequency oscllatng flow n an asymmetrc branchng arway model[j]medcal Engneerng & Physcs200931(9): [2] Klenstreuer C, Zhang ZArflow and partcle transport n the human respratory system[j]annual Revew of Flud Mechancs, 2010, [3] Luo HYLu YModelng the bfurcatng flow n a CT-scanned human lung arway[j]journal of Bomechancs2008, 41(12) [4] Goutham M, Shanmugam M, Mha M, et alvaldaton of computatonal flud dynamcs methodology used for human upper arway flow smulatons[j]journal of Bomechancs, 2009, (42) [5] Xu Xnx,, Lu YaunSmulaton study on characterstcs of the transent arflow movement n human arway at cyclc nhalaton flow[j]chnese Journal of Bomedcal Engneerng [6] Nazrdoust KAsgharan BUnsteady-state arflow and partcle deposton n a three-generaton human lung geometry y[j]inhalaton Toxcology200820(6) [7] Wolfgang AWallTmon RFlud-structure nteracton n lower arways of CT-based lung geometres[j]internatonal Journal for Numercal Methods n Fluds,2008,57(5) [8] Grgc BFnlay WHHeenan AFRegonal aerosol deposton and flow measurements n an dealzed mouth and throat[j]aerosol Scence [9] Stapleton KWGuentsch EHosknson MKet alon the sutablty of k-turbulence modelng for aerosol deposton n the mouth and throat: a comparson wth experment[j]aerosol Scence200031(6) [10] Zhang ZhaoshunCu GuxangXu ChunxaoTheory and Applcaton for Large Eddy Smulaton of turbulent flow [M]BengTsnghua Unversty [11] Zhao XuguoXu XnxTan Shuln et alpiv experment of steady flow wthn the human upper respratory tract [J] Journal of Experments n Flud Mechancs,