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Computational Biofluiddynamics: Advances and Applications
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Computational Biofluiddynamics: Advances and Applications

A special issue of Fluids (ISSN 2311-5521). This special issue belongs to the section "Mathematical and Computational Fluid Mechanics".

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 39268

Special Issue Editors

Prof. Dr. Rajat Mittal

E-Mail Website
Guest Editor
Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
Interests: computational fluid dynamics; low Reynolds number aerodynamics; biomedical flows; active flow control; LES/DNS; Immersed Boundary Methods; fluid dynamics of locomotion (swimming and flying); biomimetics and bioinspired engineering; turbomachinery flows
Prof. Dr. Hao Liu

E-Mail Website
Guest Editor
Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
Interests: computational mechanics; biofluids; biomechanics and biomimetics in flying and swimming; aeroacoustics; multi-scale and multi-physical modeling of the cardiovascular system; machine-learning and deep-learning
Special Issues, Collections and Topics in MDPI journals
Dr. Kourosh Shoele

E-Mail Website
Guest Editor
Department of Mechanical Engineering, Florida State University, Tallahassee, FL 32306, USA
Interests: bioinspired engineering; fluid-structure interaction; biomechanics and biomedical flows; wind & wave energies; computational mechanics

Special Issue Information

Dear Colleagues,

Nearly fifty years have passed since two seminal events in the chronology of biofluiddynamics: the publication of Sir James Lighthill’s seminal monograph on mathematical biofluiddynamics and the groundbreaking, immersed boundary method-based simulations of flow in a beating heart by Charles Peskin. Since then, the field of computational biofluidynamics has experienced explosive growth, with applications extending to virtually all areas of physiological fluid dynamics as well as the fluid dynamics of biolocomotion. This expansion has been powered by new physical discoveries and significant improvements in physics-based, as well as data-driven methodologies, including models that couple flow with structural dynamics, aeroacoustics, chemistry, electrodynamics, heat transfer, and other physical domains. This Special Issue of Fluids seeks to highlight recent advances in computation and data-enabled techniques in biofluiddynamics and to showcase the state of the art in the application of these methods to physiological flows, fluid dynamics of biolocomotion, and bioinspired engineering.

Prof. Dr. Rajat Mittal
Prof. Dr. Hao Liu
Dr. Kourosh Shoele
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fluids is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • computational fluid dynamics
  • physiological fluid dynamics
  • biolocomotion
  • swimming and flying
  • hemodynamics
  • bioinspired engineering
  • machine learning
  • data-enabled methods

Published Papers (15 papers)

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Research

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16 pages, 4576 KiB  
Article
Investigation of the Role of Face Shape on the Flow Dynamics and Effectiveness of Face Masks
by Tomas Solano and Kourosh Shoele
Fluids 2022, 7(6), 209; https://doi.org/10.3390/fluids7060209 - 18 Jun 2022
Cited by 2 | Viewed by 1669
Abstract
Due to the COVID-19 pandemic, face masks have been used extensively in society. The effectiveness of face masks depends on their material, design, and fit. With much research being focused on quantifying the role of the material, the design and fit of masks [...] Read more.
Due to the COVID-19 pandemic, face masks have been used extensively in society. The effectiveness of face masks depends on their material, design, and fit. With much research being focused on quantifying the role of the material, the design and fit of masks have been an afterthought at most. Recent studies, on the other hand, have shown that the mask fit is a significant factor to consider when specifying the effectiveness of the face mask. Moreover, the fit is highly dependent on face topology. Differences in face types and anthropometrics lead to different face mask fit. Here, computational fluid dynamics simulations employing a novel model for porous membranes (i.e., masks) are used to study the leakage pattern of a cough through a face mask on different faces. The three faces studied (female, male, and child) are characteristic faces identified in a previous population study. The female face is observed to have the most leakage through the periphery of the mask, which results in the lowest fitted filtration efficiency of the three faces. The male and child faces had similar gap profiles, leakage and fitted filtration efficiencies. However, the flow of the three faces differs significantly. The effect of the porosity of the mask was also studied. While all faces showed the same general trend with changing porosity, the effect on the child’s face was more significant. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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13 pages, 4742 KiB  
Article
Mitral Valve Regurgitation Murmurs—Insights from Hemoacoustic Computational Modeling
by Ziyu Wang, Jung Hee Seo and Rajat Mittal
Fluids 2022, 7(5), 164; https://doi.org/10.3390/fluids7050164 - 07 May 2022
Viewed by 1715
Abstract
Mitral regurgitation (MR) is the leakage of blood from the left ventricle into the left atrium during systole through a mitral valve that does not close fully. A systolic murmur is produced by MR and can be used to diagnose this disease. In [...] Read more.
Mitral regurgitation (MR) is the leakage of blood from the left ventricle into the left atrium during systole through a mitral valve that does not close fully. A systolic murmur is produced by MR and can be used to diagnose this disease. In the current study, we use hemoacoustic simulations to characterize the features of murmurs for a range of severities relevant to chronic MR. The incompressible Navier–Stokes equations are solved using an immersed boundary method to simulate the blood flow. The resultant pressure fluctuations on the lumen wall serve as the source for the murmur, and the murmur propagation through the thorax is modeled as a 3D elastic wave in a linear viscoelastic material. The resulting acceleration on the surface of the thorax is used as a surrogate for the measurement from a stethoscope, and these characteristics of the acceleration signal are examined in detail. We found that the intensity of the MR murmur is lower at the mitral point on the precordium, as compared with the aortic and pulmonic areas. This is somewhat counterintuitive but is supported by other studies in the past. We also found that the intensity of the murmur, as well as the break frequency, are well correlated with the severity of MR, and this information can be useful for automated auscultation and phonocardiographic applications. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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18 pages, 948 KiB  
Article
Universal Scaling Laws for Propulsive Performance of Thrust Producing Foils Undergoing Continuous or Intermittent Pitching
by Anil Das, Ratnesh K. Shukla and Raghuraman N. Govardhan
Fluids 2022, 7(4), 142; https://doi.org/10.3390/fluids7040142 - 14 Apr 2022
Cited by 1 | Viewed by 1942
Abstract
High efficiency thrust generating foils are extensively being researched for potential use as thrusters in micro air vehicles and biomimetic autonomous underwater vehicles. Here, we propose a simple reduced order model for prediction of thrust generation attributes of foils that are pitched either [...] Read more.
High efficiency thrust generating foils are extensively being researched for potential use as thrusters in micro air vehicles and biomimetic autonomous underwater vehicles. Here, we propose a simple reduced order model for prediction of thrust generation attributes of foils that are pitched either continuously or intermittently in a periodic and possibly asymmetric fashion. Our model accounts for the distinct thrust contributions from added mass, leading edge suction, quasi steady and wake terms, all deduced from a rigorous generalization of linearized potential theory to foils undergoing small amplitude multimodal flapping motion. Additionally, the model relies on Bone-Lighthill boundary layer thinning hypothesis to account for the pitching motion induced increase in the drag force exerted on the foil. We derive generic forms of the thrust coefficient for prescribed multimodal pitching motions and specifically in the limit of large reduced frequencies, demonstrate a convergence to rather simplified scaling laws that are functions of just the Reynolds number and Strouhal number based on root mean square of the foil’s trailing edge velocity. Comparisons with previously reported experimental and simulation-based investigations demonstrate that the scaling laws capture the influence of imposed pitch on thrust generation characteristics over a range of pitching waveforms ranging from sinusoidal to square or triangular-shaped waveforms and also waveforms corresponding to intermittent pitching. The generalized relations derived in our work and the asymptotic scaling laws deduced from them are applicable to a wide spectrum of self-propulsion enabling and thrust producing waveforms including the ones that can potentially be employed in burst and coast swimming. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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11 pages, 2965 KiB  
Article
Blood Flow Simulation to Determine the Risk of Thrombosis in the Fontan Circulation: Comparison between Atriopulmonary and Total Cavopulmonary Connections
by Ken-ichi Tsubota, Hidetaka Sonobe, Koichi Sughimoto and Hao Liu
Fluids 2022, 7(4), 138; https://doi.org/10.3390/fluids7040138 - 13 Apr 2022
Viewed by 2048
Abstract
Three-dimensional computational fluid dynamics (CFD) simulations were performed in the anastomotic region of the Fontan route between the venae cava and pulmonary arteries to investigate the risk of thrombosis due to blood stasis in the Fontan circulation. The finite volume method based on [...] Read more.
Three-dimensional computational fluid dynamics (CFD) simulations were performed in the anastomotic region of the Fontan route between the venae cava and pulmonary arteries to investigate the risk of thrombosis due to blood stasis in the Fontan circulation. The finite volume method based on the time-averaged continuity and Navier–Stokes equations combined with the k-ω SST turbulent model was used in the CFD simulations. Low shear rate (SR) and SR on the wall (WSR) of <10 s−1 were used as markers to assess blood stasis as a cause of blood coagulation. Simulated blood flow velocity and both SR and WSR were reduced in the right atrium (RA) as the cavity of a flow channel in the atriopulmonary connection (APC) Fontan model, whereas the values increased in the total cavopulmonary connection (TCPC) Fontan model, which has no cavity. The volume of SR <10 s−1 and wall surface area of WSR <10 s−1 were, respectively, 4.6–261.8 cm3 and 1.2–38.3 cm2 in the APC Fontan model, and 0.1–0.3 cm3 and 0.1–0.6 cm2 in the TCPC Fontan model. The SR and WSR increased in the APC model with a normal-sized RA and the TCPC model as the flow rate of blood from the inferior vena cava increased with exercise; however, the SR and WSR in the RA decreased in the APC model with a dilated RA owing to the development of a recirculating flow. These findings suggest that the APC Fontan has a higher risk of thrombosis due to blood stasis than the TCPC Fontan and a higher RA dilation is associated with a higher risk of thrombosis from a fluid mechanics perspective. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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12 pages, 23400 KiB  
Article
Thermal Effect on the Bioconvection Dynamics of Gravitactic Microorganisms in a Rectangular Cavity
by Rubén Mil-Martínez, René O. Vargas, Juan P. Escandón, Ildebrando Pérez-Reyes, Marcos Turcio, Aldo Gómez-López and Francisco López-Serrano
Fluids 2022, 7(3), 113; https://doi.org/10.3390/fluids7030113 - 17 Mar 2022
Cited by 1 | Viewed by 1948
Abstract
In this work, the dynamics of the bioconvection process of gravitactic microorganisms enclosed in a rectangular cavity, is analyzed. The dimensionless cell and energy conservation equations are coupled with the vorticity-stream function formulation. Then, the effects of the bioconvection Rayleigh number and the [...] Read more.
In this work, the dynamics of the bioconvection process of gravitactic microorganisms enclosed in a rectangular cavity, is analyzed. The dimensionless cell and energy conservation equations are coupled with the vorticity-stream function formulation. Then, the effects of the bioconvection Rayleigh number and the heating source on the dynamics of microorganisms are discussed. The results based in streamlines, concentration and temperature contours are obtained through numerical simulations considering eight different configurations of symmetrical and asymmetrical heat sources. It is concluded that microorganisms accumulate in the warmer regions and swim through the cooler regions to reach the surface. They form cells for each heat source, but at high concentrations, they form a single stable cell. The results presented here can be applied to control and to understand the dynamics of microorganisms with discrete heat sources. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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16 pages, 6294 KiB  
Article
Subject-Specific Computational Fluid-Structure Interaction Modeling of Rabbit Vocal Fold Vibration
by Amit Avhad, Zheng Li, Azure Wilson, Lea Sayce, Siyuan Chang, Bernard Rousseau and Haoxiang Luo
Fluids 2022, 7(3), 97; https://doi.org/10.3390/fluids7030097 - 06 Mar 2022
Cited by 2 | Viewed by 2913
Abstract
A full three-dimensional (3D) fluid-structure interaction (FSI) study of subject-specific vocal fold vibration is carried out based on the previously reconstructed vocal fold models of rabbit larynges. Our primary focuses are the vibration characteristics of the vocal fold, the unsteady 3D flow field, [...] Read more.
A full three-dimensional (3D) fluid-structure interaction (FSI) study of subject-specific vocal fold vibration is carried out based on the previously reconstructed vocal fold models of rabbit larynges. Our primary focuses are the vibration characteristics of the vocal fold, the unsteady 3D flow field, and comparison with a recently developed 1D glottal flow model that incorporates machine learning. The 3D FSI model applies strong coupling between the finite-element model for the vocal fold tissue and the incompressible Navier-Stokes equation for the flow. Five different samples of the rabbit larynx, reconstructed from the magnetic resonance imaging (MRI) scans after the in vivo phonation experiments, are used in the FSI simulation. These samples have distinct geometries and a different inlet pressure measured in the experiment. Furthermore, the material properties of the vocal fold tissue were determined previously for each individual sample. The results demonstrate that the vibration and the intraglottal pressure from the 3D flow simulation agree well with those from the 1D flow model based simulation. Further 3D analyses show that the inferior and supraglottal geometries play significant roles in the FSI process. Similarity of the flow pattern with the human vocal fold is discussed. This study supports the effective usage of rabbit larynges to understand human phonation and will help guide our future computational studies that address vocal fold disorders. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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18 pages, 5246 KiB  
Article
Numerical Study of Particle Margination in a Square Channel Flow with Red Blood Cells
by Dongig Oh, Satoshi Ii and Shu Takagi
Fluids 2022, 7(3), 96; https://doi.org/10.3390/fluids7030096 - 06 Mar 2022
Cited by 7 | Viewed by 2686
Abstract
Red blood cells flow near the axis in a small vessel, known as axial accumulation. This causes a region called the cell-free layer, which does not contain red blood cells near the wall. Then, small particles such as platelets come out to the [...] Read more.
Red blood cells flow near the axis in a small vessel, known as axial accumulation. This causes a region called the cell-free layer, which does not contain red blood cells near the wall. Then, small particles such as platelets come out to the cell-free layer. This phenomenon is called platelet margination. In this study, related to this phenomenon, direct numerical simulations were conducted using the immersed boundary method. The effects of the shear rate, channel size, and hematocrit value were investigated on the pressure-driven flow in a straight tube with a square cross-section. The simulation results indicated that the margination rate, which is the ratio of the distance traveled in the flow direction to the margination distance in the wall direction, is independent of the shear rate. The effect of the channel size on platelet margination was found to be well scaled by introducing a dimensionless parameter, which included the shear rate and effective area of the particle movement. It was also found that the margination rate varied nonlinearly with the tube hematocrit. This was due to the volume exclusion effect of red blood cells, which facilitated or hindered the motion of particles depending on the hematocrit. The relationship between the stable position of the particles near the corner and the width of the cell-free layer was also found. Furthermore, velocity fluctuations normalized by wall shear rate in a cross-section collapsed to one curve in the presented simulations. This indicates that the lateral force acting on the particles increases linearly with the shear rate. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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14 pages, 9116 KiB  
Article
Numerical Study of Multiple Bio-Inspired Torsionally Hinged Flaps for Passive Flow Control
by Nirmal J. Nair, Zoey Flynn and Andres Goza
Fluids 2022, 7(2), 44; https://doi.org/10.3390/fluids7020044 - 18 Jan 2022
Cited by 4 | Viewed by 2368
Abstract
Covert feathers are a set of self-actuating, passively deployable feathers located on the upper surfaces of wings that augment lift at post-stall angles of attack. Due to these benefits, the study of covert-inspired passive flow control devices is becoming an increasingly active area [...] Read more.
Covert feathers are a set of self-actuating, passively deployable feathers located on the upper surfaces of wings that augment lift at post-stall angles of attack. Due to these benefits, the study of covert-inspired passive flow control devices is becoming an increasingly active area of research. In this work, we numerically investigate the aerodynamic benefits of torsionally mounting five covert-inspired flaps on the upper surface of a NACA0012 airfoil. Two-dimensional high-fidelity simulations of the flow past the airfoil–flap system at low Re=1000 and a high angle of attack of 20∘ were performed. A parametric study was conducted by varying the flap moment of inertia and torsional hinge stiffness to characterize the aerodynamic performance of this system. Lift improvements as high as 25% were attained. Two regimes of flap dynamics were identified that provided considerable aerodynamic benefits. A detailed investigation of the flow physics of both these regimes was conducted to understand the physical mechanisms by which the passively deployed flaps augmented the lift of the airfoil. In both regimes, the flap was found to act as a barrier in preventing the upstream propagation of reverse flow due to flow separation and trailing edge vortex. The torsional spring and flap inertia yielded additional flap dynamics that further modulated the surrounding flow and associated performance metrics. We discuss some of these fluid–structure interaction effects in this article. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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19 pages, 14053 KiB  
Article
Stable Schooling Formations Emerge from the Combined Effect of the Active Control and Passive Self-Organization
by Yi Zhu, Jian-Hua Pang and Fang-Bao Tian
Fluids 2022, 7(1), 41; https://doi.org/10.3390/fluids7010041 - 17 Jan 2022
Cited by 9 | Viewed by 2212
Abstract
This work presents a numerical study of the collective motion of two freely-swimming swimmers by a hybrid method of the deep reinforcement learning method (DRL) and the immersed boundary-lattice Boltzmann method (IB-LBM). An active control policy is developed by training a fish-like swimmer [...] Read more.
This work presents a numerical study of the collective motion of two freely-swimming swimmers by a hybrid method of the deep reinforcement learning method (DRL) and the immersed boundary-lattice Boltzmann method (IB-LBM). An active control policy is developed by training a fish-like swimmer to swim at an average speed of 0.4 L/T and an average orientation angle of 0∘. After training, the swimmer is able to restore the desired swimming speed and orientation from moderate external perturbation. Then the control policy is adopted by two identical swimmers in the collective swimming. Stable side-by-side, in-line and staggered formations are achieved according to the initial positions. The stable side-by-side swimming area of the follower is concentrated to a small area left or right to the leader with an average distance of 1.35 L. The stable in-line area is concentrated to a small area about 0.25 L behind the leader. A detailed analysis shows that both the active control and passive self-organization play an important role in the emergence of the stable schooling formations, while the active control works for maintaining the speed and orientation in case the swimmers collide or depart from each other and the passive self-organization works for emerging a stable schooling configuration. The result supports the Lighthill conjecture and also highlights the importance of the active control. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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20 pages, 3251 KiB  
Article
Characterization of the Ejector Pump Performance for the Assisted Bidirectional Glenn Procedure
by Dongjie Jia and Mahdi Esmaily
Fluids 2022, 7(1), 31; https://doi.org/10.3390/fluids7010031 - 11 Jan 2022
Cited by 3 | Viewed by 2027
Abstract
This study introduces an algebraic model informed by computational fluid dynamics (CFD) simulations to investigate the performance of the assisted bidirectional Glenn (ABG) operation on a broad range of conditions. The performance of this operation, as measured by the superior vena cava (SVC) [...] Read more.
This study introduces an algebraic model informed by computational fluid dynamics (CFD) simulations to investigate the performance of the assisted bidirectional Glenn (ABG) operation on a broad range of conditions. The performance of this operation, as measured by the superior vena cava (SVC) pressure, depends on the nozzle area in its ejector pump and the patient’s pulmonary vascular resistance (PVR). Using the developed algebraic model to explore this two-dimensional parameter space shows that the ejector pump can create a pressure difference between the pulmonary artery and the SVC as high as 5 mmHg. The lowest SVC pressure is produced at a nozzle area that decreases linearly with the PVR such that, at PVR =4.2 (Wood units-m2), there is no added benefit in utilizing the ejector pump effect (optimal nozzle area is zero, corresponding to the bidirectional Glenn circulation). At PVR =2 (Wood units-m2), the SVC pressure can be lowered to less than 4 mmHg by using an optimal nozzle area of ≈2.5 mm2. Regardless of the PVR, adding a 2 mm2 nozzle to the baseline bidirectional Glenn boosts the oxygen saturation and delivery by at least 15%. The SVC pressure for that 2 mm2 nozzle remains below 14 mmHg for all PVRs less than 7 Wood units-m2. The mechanical efficiency of the optimal designs consistently remains below 30%, indicating the potential for improvement in the future. A good agreement is observed between the algebraic model and high-fidelity CFD simulations. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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13 pages, 5063 KiB  
Article
Impact of Respiratory Fluctuation on Hemodynamics in Human Cardiovascular System: A 0-1D Multiscale Model
by Ruichen Li, Koichi Sughimoto, Xiancheng Zhang, Sirui Wang, Yuto Hiraki and Hao Liu
Fluids 2022, 7(1), 28; https://doi.org/10.3390/fluids7010028 - 07 Jan 2022
Cited by 1 | Viewed by 2144
Abstract
To explore hemodynamic interaction between the human respiratory system (RS) and cardiovascular system (CVS), here we propose an integrated computational model to predict the CVS hemodynamics with consideration of the respiratory fluctuation (RF). A submodule of the intrathoracic pressure (ITP) adjustment is developed [...] Read more.
To explore hemodynamic interaction between the human respiratory system (RS) and cardiovascular system (CVS), here we propose an integrated computational model to predict the CVS hemodynamics with consideration of the respiratory fluctuation (RF). A submodule of the intrathoracic pressure (ITP) adjustment is developed and incorporated in a 0-1D multiscale hemodynamic model of the CVS specified for infant, adolescent, and adult individuals. The model is verified to enable reasonable estimation of the blood pressure waveforms accounting for the RF-induced pressure fluctuations in comparison with clinical data. The results show that the negative ITP caused by respiration increases the blood flow rates in superior and inferior vena cavae; the deep breathing improves the venous return in adolescents but has less influence on infants. It is found that a marked reduction in ITP under pathological conditions can excessively increase the flow rates in cavae independent of the individual ages, which may cause the hemodynamic instability and hence increase the risk of heart failure. Our results indicate that the present 0-1D multiscale CVS model incorporated with the RF effect is capable of providing a useful and effective tool to explore the physiological and pathological mechanisms in association with cardiopulmonary interactions and their clinical applications. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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20 pages, 10300 KiB  
Article
Computational Approach for the Fluid-Structure Interaction Design of Insect-Inspired Micro Flapping Wings
by Daisuke Ishihara
Fluids 2022, 7(1), 26; https://doi.org/10.3390/fluids7010026 - 06 Jan 2022
Cited by 12 | Viewed by 2240
Abstract
A flight device for insect-inspired flapping wing nano air vehicles (FWNAVs), which consists of the micro wings, the actuator, and the transmission, can use the fluid-structure interaction (FSI) to create the characteristic motions of the flapping wings. This design will be essential for [...] Read more.
A flight device for insect-inspired flapping wing nano air vehicles (FWNAVs), which consists of the micro wings, the actuator, and the transmission, can use the fluid-structure interaction (FSI) to create the characteristic motions of the flapping wings. This design will be essential for further miniaturization of FWNAVs, since it will reduce the mechanical and electrical complexities of the flight device. Computational approaches will be necessary for this biomimetic concept because of the complexity of the FSI. Hence, in this study, a computational approach for the FSI design of insect-inspired micro flapping wings is proposed. This approach consists of a direct numerical modeling of the strongly coupled FSI, the dynamic similarity framework, and the design window (DW) search. The present numerical examples demonstrated that the dynamic similarity framework works well to make different two FSI systems with the strong coupling dynamically similar to each other, and this framework works as the guideline for the systematic investigation of the effect of characteristic parameters on the FSI system. Finally, an insect-inspired micro flapping wing with the 2.5-dimensional structure was designed using the proposed approach such that it can create the lift sufficient to support the weight of small insects. The existing area of satisfactory design solutions or the DW increases the fabricability of this wing using micromachining techniques based on the photolithography in the micro-electro-mechanical systems (MEMS) technology. Hence, the proposed approach will contribute to the further miniaturization of FWNAVs. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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18 pages, 5027 KiB  
Article
Computational Analysis of Lung and Isolated Airway Bifurcations under Mechanical Ventilation and Normal Breathing
by Jongwon Kim and Ramana M. Pidaparti
Fluids 2021, 6(11), 388; https://doi.org/10.3390/fluids6110388 - 29 Oct 2021
Cited by 3 | Viewed by 2025
Abstract
Mechanical ventilation is required for many patients who cannot breathe normally as a result of lung disease and other factors that result in reduced lung function. In this study, we investigated the effects of mechanical ventilation and normal breathing on whole lung geometry [...] Read more.
Mechanical ventilation is required for many patients who cannot breathe normally as a result of lung disease and other factors that result in reduced lung function. In this study, we investigated the effects of mechanical ventilation and normal breathing on whole lung geometry as well as isolated bifurcations through computational fluid dynamic (CFD) simulations. Results of flow characteristics (airflow velocity, wall pressure, and wall shear stress) obtained from the CFD simulations are presented. Similar flow patterns and pressure drops were obtained between the whole lung geometry and isolated bifurcations under both normal breathing and mechanical ventilation, respectively. Results obtained from simulations suggest that analyzing specific local bifurcations may be a more feasible alternative as it may reduce the computational time and numerical errors resulting from computations as compared to simulating a complex whole lung geometry. The approach presented in this study also demonstrated that analyses of isolated bifurcations gave similar flow characteristics to that of whole lung geometry. Therefore, this approach may be useful for quickly obtaining results that will assist in making clinical predictions and other applications. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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16 pages, 5297 KiB  
Article
Geometry and Flow Properties Affect the Phase Shift between Pressure and Shear Stress Waves in Blood Vessels
by Haifeng Wang, Timm Krüger and Fathollah Varnik
Fluids 2021, 6(11), 378; https://doi.org/10.3390/fluids6110378 - 23 Oct 2021
Cited by 6 | Viewed by 2940
Abstract
The phase shift between pressure and wall shear stress (WSS) has been associated with vascular diseases such as atherosclerosis and aneurysms. The present study aims to understand the effects of geometry and flow properties on the phase shift under the stiff wall assumption, [...] Read more.
The phase shift between pressure and wall shear stress (WSS) has been associated with vascular diseases such as atherosclerosis and aneurysms. The present study aims to understand the effects of geometry and flow properties on the phase shift under the stiff wall assumption, using an immersed-boundary-lattice-Boltzmann method. For pulsatile flow in a straight pipe, the phase shift is known to increase with the Womersley number, but is independent of the flow speed (or the Reynolds number). For a complex geometry, such as a curved pipe, however, we find that the phase shift develops a strong dependence on the geometry and Reynolds number. We observed that the phase shift at the inner bend of the curved vessel and in the aneurysm dome is larger than that in a straight pipe. Moreover, the geometry affects the connection between the phase shift and other WSS-related metrics, such as time-averaged WSS (TAWSS). For straight and curved blood vessels, the phase shift behaves qualitatively similarly to and can thus be represented by the TAWSS, which is a widely used hemodynamic index. However, these observables significantly differ in other geometries, such as in aneurysms. In such cases, one needs to consider the phase shift as an independent quantity that may carry additional valuable information compared to well-established metrics. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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Review

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25 pages, 15387 KiB  
Review
Computational Methods for Fluid-Structure Interaction Simulation of Heart Valves in Patient-Specific Left Heart Anatomies
by Trung Bao Le, Mustafa Usta, Cyrus Aidun, Ajit Yoganathan and Fotis Sotiropoulos
Fluids 2022, 7(3), 94; https://doi.org/10.3390/fluids7030094 - 04 Mar 2022
Cited by 6 | Viewed by 5410
Abstract
Given the complexity of human left heart anatomy and valvular structures, the fluid–structure interaction (FSI) simulation of native and prosthetic valves poses a significant challenge for numerical methods. In this review, recent numerical advancements for both fluid and structural solvers for heart valves [...] Read more.
Given the complexity of human left heart anatomy and valvular structures, the fluid–structure interaction (FSI) simulation of native and prosthetic valves poses a significant challenge for numerical methods. In this review, recent numerical advancements for both fluid and structural solvers for heart valves in patient-specific left hearts are systematically considered, emphasizing the numerical treatments of blood flow and valve surfaces, which are the most critical aspects for accurate simulations. Numerical methods for hemodynamics are considered under both the continuum and discrete (particle) approaches. The numerical treatments for the structural dynamics of aortic/mitral valves and FSI coupling methods between the solid Ωs and fluid domain Ωf are also reviewed. Future work toward more advanced patient-specific simulations is also discussed, including the fusion of high-fidelity simulation within vivo measurements and physics-based digital twining based on data analytics and machine learning techniques. Full article
(This article belongs to the Special Issue Computational Biofluiddynamics: Advances and Applications)
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