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A structure-level smart deployable truss (SDT) was further studied for on-orbit verification on the SJ18 Geostationary Satellite in this work on the basis of a material-level validation of a shape-memory polymer composite (SMPC) sheet on the SJ17 Geostationary Satellite in 2016. In the SDT, a shape-memory alloy (SMA) mechanism was used to replace traditional pyrotechnic devices for locking and releasing, and SMPC actuation laminates were employed to replace traditional motor or spring driving mechanisms. With a strict parameter constrain of mass, size, and stiffness, the current form of the SDT flight hardware was finally obtained through several cycles of optimization design. Its systematical ground-based experiments were conducted, and the overall structural and functional performance met the demands of the aerospace standards of China. The locking force and expansion breaking force of the SMA releasing mechanism were [Formula: see text] and [Formula: see text], ensuring the locking and unlocking reliability for the movable parts with mass 5 kg. The actuation force of all SMPC laminates decreased from [Formula: see text] (0°) to [Formula: see text] (165°) with a recovery duration of [Formula: see text], which was strong enough for SDT deployment in space. The shape-memory materials show great prospects for smart deployable structures in space.

Physics-Informed Neural Networks (PINNs) are becoming more and more popular for solving partial differential equations (PDEs) of nonlinear systems. Due to the advantage of low computational cost, the gradient descent algorithm coupled with the weighted objectives method is usually used to optimize loss functions in the PINN training. However, the interaction mechanisms between the gradients of loss functions are not fully clarified, leading to poor performances in loss functions optimization such as low efficiency and non-convergence. For this, an adaptive gradient descent algorithm (AGDA) is proposed, and then validated by analytical PDEs and Navier-Stokes equations. Firstly, the interaction mechanisms of loss functions gradients in the PINN training based on the traditional Adam optimizer are analyzed. The main factors responsible for the poor performances of the Adam optimizer are identified. Based on the interaction mechanisms, a new AGDA optimizer is developed for the PINN training by two steps: 1) balancing the magnitude difference of loss functions gradients; 2) eliminating the gradient directions conflict. Then, three types of PDEs (elliptic, hyperbolic and parabolic) and three twodimensional incompressible Navier-Stokes equations are selected to validate the proposed algorithm. It is found that the AGDA optimizer can achieve higher training accuracy with fewer iterations, and can improve the training efficiency of the analytical PDEs by 5~6 times and the multi-parameter NavierStokes equations by 1.4 times. Also, the AGDA optimizer is more robust as it performs better than the traditional Adam optimizer in dealing with the parabolic heat conduction equation and the unsteady Navier-Stokes equation.

As a typical black-box problem, recirculating casing treatment (RCT) optimization of compressor stages is computationally intensive and time consuming, even though surrogate models are usually employed. In order to improve efficiency and robustness of the optimization, an expected-improvement (EI) based hybrid global optimization (EHGO) algorithm is developed by coupling an EI-based surrogate model with a hybrid optimization algorithm. Highly nonlinear and multiple modality mathematical tests show that the EHGO algorithm is able to create a high-fidelity surrogate model near targeted regions with less evaluated samples, and to obtain the global optimal solution simultaneously. The RCT of a compressor stage is optimized based on this algorithm. The number of CFD simulations required for obtaining an optimum solution is greatly reduced, as compared to similar studies using conventional methods. The optimization results show that the aerodynamic performance is improved over the whole speed line and the flow range is also extended. The dominant factors for the performance improvements and the enhanced stall margin are addressed by analyzing the local flow characteristics before and after optimization. It is found that those factors include: removing a larger amount of low-momentum fluid, achieving a more uniform flow of impeller passage in circumferential direction, and reducing the radial distortion of impeller inlet flow. The proposed algorithm has the potential to considerably speed up the optimization process and make the optimization much more accessible. It can be generalized to deal with other computationally intensive black-box problems, for example, turbomachinery optimization.

In consideration of the turbulent inflow condition of engineering applications, the flow mechanisms of dynamic stall of a tubercled airfoil have been comprehensively analyzed with an upstream cylinder. Numerical simulation of the flowfield of a tubercled wing with NACA0021 (National Advisory Committee for Aeronautics) airfoil has been conducted with the large eddy simulation model. Then, flow mechanisms have been analyzed based on the aerodynamic performances and flow structure descriptions. Meanwhile, proper orthogonal decomposition (POD) analysis has been carried out at both trough and peak sections to reveal the flow dynamics. It turns out that the dynamic stall process vanishes, and performances would be obviously impacted by the incoming cylinder wake in the case of [Formula: see text] due to the enforced resistance of adverse pressure gradient. Furthermore, the first leading POD mode corresponds to the pitching movement at both trough and peak sections, while the high-order modes represent the influence of cylinder wake. Eventually, the influence of pitching amplitude has also been discussed in the case of [Formula: see text]. Different from the case of [Formula: see text], dynamic stall phenomenon emerges, and the influence of wake impingement could be barely detected from the mode information except for the third mode at the trough section. The detachment of the dynamic stall vortex takes place corresponding to the dynamic stall onset, which is driven by the streamwise pressure gradient near the trough leading-edge.

A new approach to predict the performance maps of automotive turbocharger compressors is presented. Firstly, a polynomial equation is applied to fit the experimental data of flow coefficient ratios for the centrifugal compressors with both vaneless and vaned diffusers. Based on this equation, the choke and surge flow coefficients under different machine Mach numbers can be quickly predicted. Secondly, a physically based piecewise elliptic equation is used to define compressors’ characteristic curves in terms of efficiency ratio. By introducing the flow coefficient ratio into the efficiency correlation, the empirical coefficients in the piecewise elliptic equation are uniquely calibrated by the experimental data, forming a unified algebraic equation to match the efficiency maps of the compressors with both vaneless and vaned diffusers. Then, a new universal equation, which connects the work coefficient, the impeller outlet flow coefficient and the non-dimensional equivalent impeller outlet width, is derived by using classical aerothermodynamic method. The off-design pressure ratio is predicted based on the equivalent impeller outlet width with less knowledge of the compressor geometry and no empirical coefficients. Finally, three state-of-the-art turbocharger compressors (one with vaneless diffuser, two with vaned diffusers) are chosen to validate the proposed method, and the results show a satisfactory accuracy for the performance map prediction. This method can be used for the preliminary design of turbocharger compressors with both vaneless and vaned diffusers, or to assess the design feasibility and challenges of the given design specifications.

The forced convection (air supply jet) and the natural convection (thermal plume of passenger) co-exist in an aircraft cabin simultaneously. Due to the notable difference of the Reynolds numbers for the two convection processes, the traditional RANS method can hardly simulate the forced/natural convection flows accurately at the same time. In addition, the large geometric ratio between the main air supply inlet and the whole cabin leads to difficulties in grid generation for the cabin space. An efficient computational model based on the standard k-e model is established to solve these problems. The coefficients in the dissipative equation are modified to compensate the enlarged numerical dissipation caused by coarse grid; meanwhile, the piecewise-defined turbulent viscosity is introduced to combine the forced and natural convection. The modified model is validated by available experimental results in a Boeing 737-200 mock-up. Furthermore, the unsteady characteristic of the aircraft cabin environment is obtained and analyzed. According to the frequency analysis, it turns out that the thermal plume is the main factor of the unsteady fluctuation in cabin.Supplementary material is available in the online version of this article at 10.1007/s12273-020-0609-2.

To understand the flow dynamic characteristics of a centrifugal compressor, the dynamic mode decomposition (DMD) method is introduced to decompose the complex three-dimensional flow field. Three operating conditions, peak efficiency (OP1), peak pressure ratio (OP2), and small mass flow rate (near stall, OP3) conditions, are analyzed. First, the physical interpretations of main dynamic modes at OP1 are identified. As a result, the dynamic structures captured by DMD method are closely associated with the flow characteristics. In detail, the BPF/2BPF (blade passing frequency) corresponds to the impeller–diffuser interaction, the rotor frequency (RF) represents the tip leakage flow (TLF) from leading edge, and the 4RF is related to the interaction among the downstream TLF, the secondary flow, and the wake vortex. Then, the evolution of the dynamic structures is discussed when the compressor mass flow rate consistently declines. In the impeller, the tip leakage vortex near leading edge gradually breaks down due to the high backpressure, resulting in multi-frequency vortices. The broken vortices further propagate downstream along streamwise direction and then interact with the flow structures of 4RF. As a result, the 8RF mode can be observed in the whole impeller, this mode is transformed from upstream RF and 4RF modes, respectively. On the other hand, the broken vortices show broadband peak spectrum, which is correlated to the stall inception. Therefore, the sudden boost of energy ratio of 14RF mode could be regarded as a type of earlier signal for compressor instability. In the diffuser, the flow structures are affected by the perturbation from the impeller. However, the flow in diffuser is more stable than that in impeller at OP1–OP3, since the leading modes are stable patterns of BPF/2BPF.

The overall trend of centrifugal compressor design is to strive for high aerodynamic performance and high flow capacity products. A new methodology is derived to implement a preliminary design for high flow capacity centrifugal impeller with and without prewhirl. First, several new non-dimensional equations connecting impeller geometric and aerodynamic parameters are derived for the maximum flow capacity. The effects of prewhirl on mass flow function, inlet diameter ratio and work coefficient are discussed, respectively. Then, based on these equations, a series of design diagrams are drawn to extract the universal rules in centrifugal impeller design with prewhirl. Some physical limits of design maps are also discussed. Finally, the throat area of impeller is discussed under prewhirl, and the matching principle between prewhirl impeller and vaned diffuser is derived and validated. The proposed method can be used to design a new centrifugal compressor, or to evaluate the design feasibility and the challenge of a given design specification.

A new multi-objective, multi-disciplinary global optimization strategy is proposed to address the high-dimensional, computationally expensive black box problem (HEB) in turbomachinery design. The strategy consists of an adaptive sampling hybrid optimization algorithm (ASHOA), two data-mining techniques, a 3D blade parameterization method, and the aerodynamic/mechanical codes. Firstly, the ASHOA is established by integrating a novel adaptive sampling Kriging metamodel and a new hybrid optimization method. Secondly, two data-mining methods (analysis of variance (ANOVA) and self-organizing map (SOM)) are applied to set the initial design space and optimization objectives of the transonic centrifugal compressor. A refined design space and objective parameters of the optimization problem are eventually obtained. Finally, the optimization process of a transonic centrifugal compressor is carried out based on the refined design space and objectives using ASHOA. The results show that the search efficiency of the optimization strategy is 2–10 times higher when compared to other excellent optimization algorithms. For the optimized compressor, both isentropic efficiency and total pressure ratio at design condition are improved by 1.61% and 4.13%, respectively, and the maximum stress decreases by 9.68%.

The numerical analysis method of Proper Orthogonal Decomposition (POD) is usually used to decompose the correlated nonlinear flow field and extract the structures with maximum energy contents (also called POD modes). However, it tends to mix the temporal frequencies in most modes, which confuses the physical interpretation and makes the flow dynamic characteristics unclear. For the transient flow field with discrete frequencies, to obtain the coherent structures with single-frequency dynamic characteristics, a new single-frequency POD method (F-POD) is proposed by utilizing Discrete Fourier Transform (DFT) and the corresponding inverse operation. In this way, the POD modes can be re-decomposed from the perspective of frequency. Particularly, for the spectra with a band of adjacent frequencies around some isolated peaks, the selection criterion of the frequency range in the inverse operation process is discussed to obtain the growth rate information of the modes. To illustrate the feasibility of F-POD, several multi-frequencies analytical cases with various growth patterns and a transitional cylinder wake case are investigated. In addition, the results are quantitatively compared with dynamic mode decomposition (DMD). It shows that the single-frequency POD modes with temporal evolutions can be well distinguished. Therefore, for the transitional flow scenarios with discrete frequencies, the F-POD could be an alternative method to extract the dynamic coherent structure with single-frequency and growth rate. We also found that the F-POD has challenges to deal with broadband turbulence, since it is hard to find main frequency.

Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.

Smart structures based on shape memory polymer composites (SMPCs) have attracted extensive attention because of their unique self-deployment behavior. This study investigated the thermal design and analysis of the SMPC flexible solar array system (SMPC-FSAS). The thermal design ensured the reliability of the deployment functionality and desirable structural temperatures. The fundamental properties of the shape-memory materials were obtained by dynamic mechanical analysis and shape fixity ratio tests. Thermal experiments, including the thermal balance test (TBT), thermal vacuum test and thermal cycle test were conducted to verify the safety and reliability of the SMPC-FSAS. Additionally, the temperature distribution of the SMPC-FSAS was simulated using numerical analysis. Notably, a geostationary satellite carrying the SMPC-FSAS was successfully launched into a geosynchronous orbit and controlled deployment was accomplished for the first time. The prediction of the numerical model was consistent with the TBT and on-orbit data, thus validating the accuracy of the numerical method. The research in this work has important reference significance for ultra-large SMPC-FSAS in the future.

In this paper, the numerical dispersion of a hierarchical reconstruction strategy for DG/FV method has been optimized. For the hierarchical strategy, the cell averages and the first derivatives are reconstructed based on the Hermite WENO method; the second derivatives are reconstructed via Green-Gauss integration and WENO reconstruction. Then, the numerical dispersion has been optimized by minimizing error with bandwidth optimization technique. Furthermore, to adjust the loss of compactness due to the reconstructed second derivatives, two modifications were also proposed with optimal weights. Eventually, from the implementations in scalar and compressible Euler equations, the superiority of numerical dispersion and accuracy of present methods could be validated. The shock capturing capacity has also been validated in 1D and 2D cases.

This article implements the thermodynamic design space data-mining and multi-objective optimization of two typical supercritical carbon dioxide (SCO2) Brayton cycles: the recompression Brayton cycle (SCO2RBC) and the recompression reheating Brayton cycle (SCO2RRBC). Firstly, a mathematical model with more constraints has been established for the two Brayton cycles. The maximum errors of the mathematical model relative to the references for the SCO2RBC and SCO2RRBC are 2.5%, 3.5% respectively. Then, three data-mining techniques (global sensitivity analysis by ANOVA, single factor analysis, coupling analysis by SOM) are successively applied to explore the design space. As a result, four key design parameters have been identified: the maximum and the minimum cycle temperatures, the pressure ratio, and the shunt flow percentage. And they present different non-linear effects on the cycles’ performances (monotone increasing or decreasing, parabolic type with extreme point). It is also found that in order to achieve a global optimum, the maximum cycle temperature should be close to its upper bound, while the minimum cycle temperature tends to approach its lower bound, and a larger pressure ratio of compressor as well as a smaller shunt flow percentage is also required. Therefore, the data-mining methods are heuristic and can provide useful information for quickly searching the global optimums of SCO2 Brayton Cycles. Finally, a hybrid optimization algorithm is introduced to optimize the Brayton cycles. It shows that the search efficiency of the hybrid algorithm is 3 ∼ 4 times higher than the traditional stochastic algorithms. For the given design space, the cycle efficiency of the SCO2RRBC is improved by 10 percentage points. The hybrid algorithm coupled with the data-mining techniques are likely to speed up the design process of Brayton cycles, and have the potential to further improve the cycles’ performances.

The poor performance of carbon fiber composite honeycomb structures in thermal conduction is hindering their wider adoption in the high-end heat dissipation field. This paper presents a fabrication strategy for a multifunctional carbon fiber honeycomb sandwich structure (MCFHS) that can effectively dissipate the heat and bear the load. The theoretical models are derived for predicting the thermal conductivity and strength of MCFHS for out-of-plane compression loadings, which show a reasonable agreement with experiment. And experiments for point heat source and surface heat source are designed for researching the thermal dissipation capacity of MCFHS. It proves that MCFHS possess excellent thermal and mechanical performance. And the fabrication strategy has the potential to provide new opportunities for lightweight multifunctional honeycombs.

The mechanical properties and electromagnetic parameter of quartz fiber composite honeycombs (QFCH) with different equivalent densities were studied. Equivalent permittivity of the QFCH was inversed according to the transmission efficiency, which was tested by the Naval Research Laboratory Arch (NRL-arc) method. The strengths of QFCH under out-of-plane compressive and in-plane shear loading were predicted and measured. The failure mechanism map was established to predict the main failure modes of QFCH. Meanwhile, the numerical simulation was used to verify the accuracy of failure mechanism map. The QFCH designed in this study has extremely low permittivity and excellent mechanical properties, which has immense potential to be used as a 3-D metamaterial mechanical framework and more competitive in the vigorous development of new generation radomes.

Human thermal plume is quite important to the study of airflow organization in the indoor environment, especially in the micro-environment research such as personalized ventilation, infectious disease transmission through air, etc. In order to investigate the unsteady fluctuation of the thermal plume around human body, a series of transient numerical simulations are conducted in this study. Numerical simulation based on 9.7 million grids and 0.02 s time step is performed to obtain the detail quantitative data of flow field. The obvious fluctuation and separation are captured in the upper flow region of human body based on the high resolution grids. The maximum time-averaged velocity of the thermal plume is found to be 0.25 m/s while the maximum fluctuate velocity is about 0.07 m/s. The further analysis of frequency spectrum shows that the thermal plume around the body is mainly dominated by the low frequency fluctuation which is lower than 1 Hz and the principal frequency is around 0.1 Hz. In order to overcome the drawback of the high computation cost for application of the engineering simulation, a new numerical simulation method combining a modified k–e turbulence model and coarse grids is presented. This modified k–e model can reduce the calculation error of Reynolds stress in the flow region of natural convection through redefining the turbulence viscosity coefficient segmentally and avoid a high numerical viscosity appeared due to the central difference scheme. It can reasonably predict the general fluctuation velocity and the frequency distribution during simulation process in coarse grids and show a huge potential to be applied to the engineering application.

A numerical investigation of the flow mechanisms and fluctuating aerodynamic performances of an airfoil with leading-edge protuberances is presented within post-stall regime at a Reynolds number of 1.2 × 10 5 . In detail, a large eddy simulation (LES) has been conducted and then validated through quantitative comparisons with experimental and numerical results. Furthermore, dynamic mode decomposition (DMD) analysis has been carried out. Superior to the proper orthogonal decomposition (POD) method, DMD could extract mode with single-frequency characteristics. Therefore, the physical backgrounds of corresponding modes could be identified, and the flow control mechanisms could be uncovered, together with the influence on spanwise coherent structures. From the analysis at a streamwise section near laminar separation bubbles (LSBs), it has been found that the improved aerodynamic characteristics at peaks stem from the strong streamwise vortices induced by leading-edge protuberances, which lead to momentum transfer process from troughs to neighboring peaks. Meanwhile, DMD modes corresponding to the shear layers of LSBs have also been found, and the frequency characteristics are quantitatively depicted. On the other hand, from the analysis at selected lateral slices, the first DMD mode of smooth airfoil case is obviously related with Karman vortex shedding process according to the spatial distribution and frequency characteristics. Although wavy leading-edge causes the breakdown of spanwise coherent structures and the degradation of flow energy, Karman vortex shedding pattern could also be identified at particular troughs in modified airfoil case.

The unsteady numerical simulation was conducted to investigate the unsteady thermal plume around human body in closed space, with a relative high resolution of grid and time step. The instantaneous flow filed evolution process was successfully analyzed in detail by simulation approach. A set of time-average statistics of the velocity and the temperature of thermal plume around body were obtained, as well as the fluctuation velocity, the fluctuation temperature and other unsteady characteristics. The thickness of velocity and thermal boundary layer was confirmed in the range of 2 to 5 cm, the lower half of the flow field was stable whereas obvious fluctuation and separation were found in the upper half. According to the analysis results of power spectrum, the thermal plume around the body was mainly dominated by low frequency fluctuation flow, while obvious intermittent was also observed.

The design of high efficiency, high pressure ratio, and wide flow range centrifugal impellers is a challenging task. The paper describes the application of a multiobjective, multipoint optimization methodology to the redesign of a transonic compressor impeller for this purpose. The aerodynamic optimization method integrates an improved nondominated sorting genetic algorithm II (NSGA-II), blade geometry parameterization based on NURBS, a 3D RANS solver, a self-organization map (SOM) based data mining technique, and a time series based surge detection method. The optimization results indicate a considerable improvement to the total pressure ratio and isentropic efficiency of the compressor over the whole design speed line and by 5.3% and 1.9% at design point, respectively. Meanwhile, surge margin and choke mass flow increase by 6.8% and 1.4%, respectively. The mechanism behind the performance improvement is further extracted by combining the geometry changes with detailed flow analysis.

In working state, the dynamic performance of dry gas seal, generated by the rotating end face with spiral grooves, is determined by the open force of gas film and leakage flow rate. Generally, the open force and the leakage flow rate can be obtained by finite element method, computational fluid dynamics method and experimental measurement method. However, it will take much time to carry out the above measurements and calculations. In this paper, the approximate model of parallel grooves based on the narrow groove theory is used to establish the dynamic equations of the gas film for the purpose of obtaining the dynamic parameters of gas film. The nonlinear differential equations of gas film model are solved by Runge-Kutta method and shooting method. The numerical values of the pressure profiles, leakage flux and opening force on the seal surface are integrated, and then compared to experimental data for the reliability of the numerical simulation. The results show that the numerical simulation curves are in good agreement with experimental values. Furthermore, the opening force and the leakage flux are proved to be strongly correlated with the operating parameters. Then, the function-coupling method is introduced to analyze the numerical results to obtain the correlation formulae of the opening force and leakage flux respectively with the operating parameters, i.e., the inlet pressure and the rotating speed. This study intends to provide an effective way to predict the aerodynamic performance for designing and optimizing the groove styles in dry gas seal rapidly and accurately.

In this paper, shape memory polymer (SMP) and continuous carbon fibers (CCF) were utilized as raw materials to manufacture composites by means of 3D printing based on FDM. Various process parameters were systematically studied by the orthogonal experiment to find out the optimal process combination where interfaces and mechanical properties of printed composites specimens were treated as research objectives. The influence of each factor on the performance of the specimen was discussed. The results indicated that the mechanical properties were preferable when the printing temperature was 200°C, the printing speed was 4.5mm/s, the scanning pitch was 1.1 mm, and the ply stacking sequence was 0°. Furthermore, the fiber content had little effect on the shape memory performance of the polymer matrix. The rapid manufacture of shape memory carbon fiber composites has potential use in the field of aerospace.

Centrifugal compressors with high aerodynamic performance are widely used in turbochargers, aero-engines and petrochemical engineering. The impeller is the core component and plays a key role in determining the compressor performance. This paper reports the optimisation of the aerodynamic performance of an industrial centrifugal impeller by a multi-objective evolutionary strategy. Firstly the 3-D modeling method for parameterisation of impeller’s geometry was described. Secondly the traditional NSGA-II method was modified to improve its ability and efficiency. Employed CFD code was first validated using the experimental data of an existing impeller. The optimisation was applied to the industrial centrifugal impeller through a two-step optimization process to allow for significant variations of the impeller geometry and speedy finding of the optimum. The optimisation was completed within 53 hours on a workstation with two 24-core processors (Xeon(R) E5-2670 v3 2.3GHz). The results indicated that the isentropic efficiency of the impeller increased by 5.3 percents and the total pressure ratio by 20.5 percents at design condition.

In this study, fluid-structure interaction method and nonlinear deformation as well computational fluid dynamics computation was used to analyze the dynamic motion of a single cell cultured in rectangular chamber. Due to the influence of gravity, the cells moved slowly toward the bottom of the flow chamber, and it was found that cells did not directly hit the bottom during the process of descending, in contrast, the cells rebound at a certain distance from the bottom, which was designated as cell jumping phenomenon. When the cells rebound to a certain level of height, they began to move toward to bottom of chamber and then jump again. This cell jumping phenomenon occurred repeatedly and each cycle of descending and ascending was similar. When the cell movement suddenly changed, the force acting on the cells and the speed of the cells were altered in an oscillating manner. The results provide a quantitative assessment of the relationship between micro-mechanics environment and cells in vitro.

A second-order mixing difference scheme with a limiting factor is deduced with the reconstruction gradient method and applied to discretizing the Navier-Stokes equation in an unstructured grid. The transform of nonorthogonal diffusion items generated by the scheme in discrete equations is provided. The Delaunay triangulation method is improved to generate the unstructured grid. The computing program based on the SIMPLE algorithm in an unstructured grid is compiled and used to solve the discrete equations of two types of incompressible viscous flow. The numerical simulation results of the laminar flow driven by lid in cavity and flow behind a cylinder are compared with the theoretical solution and experimental data respectively. In the former case, a good agreement is achieved in the main velocity and drag coefficient curve. In the latter case, the numerical structure and development of vortex under several Reynolds numbers match well with that of the experiment. It is indicated that the factor difference scheme is of higher accuracy, and feasible to be applied to Navier-Stokes equation.

A theoretical analysis of micro motion of particles under the action of thermophoresis in aqueous electrolyte solution is presented in this paper. A two-dimensional, incompressible and laminar fluid flow model is proposed to simulate the fluid flow and particle motion trajectory in micro-channel. The effects of thermophoretic force and viscous force on the particle are calculated. The particle trajectories considering the effects of particle size, inlet flow velocity and temperature difference between bottom side and top side in micro-channel with a length of 2000 μm and a height of 500 μm are simulated. The effect of thermophoresis on separation motion of particles in micro-channel is analyzed. The results show that thermophoretic force increases with the increase of temperature gradient in micro-channel and particles with smaller diameter, smaller density and smaller gravity acceleration can pass the micro-channel more easily.

Media perfusion bioreactor systems have been developed to culture tissue cells throughout 3D tissue engineered scaffold in vitro, which enhance the exchange of nutrients and wastes and deliver flow-mediated shear stresses to cells. Stress and strain field acting on the engineered cells is the outcome of several factors, such as characterization of the scaffold, medium flow rate and the interaction of hydrodynamic flow and the scaffold wall. We develop a nonlinear fluid and solid interaction (FSI) model of the flow of culture medium through a 3D scaffold of homogeneous geometry, with the aim of predicting the stress and strain field acting on the surface of engineered cells. We built three groups of models corresponding to three pore sizes: 50, 100 and 150μ m. Each group is made of four models corresponding to 61%, 65%,77% and 84% porosity. FORTRAN and C languages are used to solve this nonlinear FSI problem. A circular scaffold of 15.5mm diameter scaffold is perfused by a flow rate of 0.5ml/min. The simulation shows that the method without regards to the effect of solid deformation to flow field is not reasonable. The high shear stress areas decrease with the increase of pore size but the shear stress looks independent of the porosity on the wall. With the increase of pore size and porosity, the maximum and average values of equivalent normal strain and equivalent shear strain become lower. More larger of porosity and pore size, more forced distribution and smaller range for equivalent normal strain field and shear strain field. This modeling approach provides a quantitative assessment of the relationship between micro mechanics environment and tissue growth in vitro.