A facile ionic liquid approach to prepare cellulose fiber with good mechanical properties directly from corn stalks

It is very difficult to directly spin the lignocellulose without pretreatment.Ionic liquids(ILs)are promising solvent to dissolve lignocellulose to prepare cellulose fiber.However,the degree of cellulose polymerization(DP)is reduced when lignocellulose is dissolved in ILs,and the lignin removal rate is low.The elongation at break and tensile strength of the fibers obtained by spinning the lignocellulose dissolved in ILs are poor.In this paper,preparing cellulose fiber directly from lignocellulose based on dissolving corn stalk via[C4mim]Cl-L-arginine binary system is achieved.It shows that the removal rate of lignin can reach 92.35%and the purity of cellulose can reach 85.32%after corn stalk was dissolved at 150℃C for 11.5 h when the mass fraction of arginine is 2.5%.The elongation at break of fiber reached 10.12%and the tensile strength reached 420 MPa.It is mainly due to the fact that L-arginine not only inhibits the degradation of cellulose but also promotes the delignination.Without any pulping or pretreatment,preparing cellulose fibers via direct dissolution and extrusion may provide a simple and effective way to prepare many novel cellulose materials.

High temperature effects in moving shock reflection with protruding Mach stem

The influence of high temperature effects on the protrusion of Mach stem in strong shock reflection over a wedge was numerically investigated. A two-dimensional inviscid solver applies finite volume method and unstructured quadrilateral grids were employed to simulate the flow. Theoretical analysis was also conducted to understand the phenomenon. Both numerical and theoretical results indicate a wall-jet penetrating forward is responsible for the occurrence of Mach stem protrusion. The protrusion degree seems to depend on the thermal energy buffer capacity of the testing gas. Approaches to increase the energy buffer capacity, such as vibrational relaxation, molecular dissociation, and increase of frozen heat caoacitv, all tend to escalate the orotrusion effect.

Tomography-like flow visualization of a hypersonic inward-turning inlet

The flow field in a typical inward-turning inlet was visualized using the Planar Laser Scattering(PLS)method in a shock tunnel with a nominal Mach number of 6.The opaque inlet,which is truncated at a series of sections,and the following transparent isolator,are combined to enable the optical access at different streamwise locations.The sequential PLS images provide a tomography-like flow visualization,which confirm the existence of streamwise Counter-rotating Vortex Pairs(CVPs)in both external and internal flow field of the inlet.Generation mechanisms of these CVPs are unraveled with the help of a numerical simulation,among which the cowl notch plays an important role in the generation of surface trailing CVPs along the centerline of the cowl.Moreover,the cowl shock sweeps the internal boundary layer towards the body side,which ultimately accumulates low-momentum flow on the body side in forms of a large CVP propagating downstream through the isolator.The CVPs formed in the shape-transition are responsible for the nonuniform flow field of the inward-turning inlet.This study indicates that the V-shaped cowl notch affects the downstream flow significantly and,therefore,should be examined thoroughly in practical applications.

Effects of trips on the oscillatory flow of an axisymmetric hypersonic inlet with downstream throttle

Experimental investigations are conducted on an axisymmetric hypersonic inlet to evaluate the effects of trips on oscillatory flows. The model exit is throttled with a fixed block to generate oscillatory flows at a freestream Mach number of 6 in a conventional wind tunnel and a shock tunnel. Schlieren imaging and pressure measurements are adopted to record unsteady flow features.Results indicate that trips with a 1 mm thickness prominently suppress external separations, shorten oscillatory cycles, and modify pressure magnitudes. Trips can reduce the upstream movement ranges of separated shocks from nose regions to locations axially 142 mm downstream. The oscillatory cycles are shortened from 3.75 ms to 3.25 ms and from 4 ms to 3.13 ms in two facilities.Tripped cases generally exhibit higher pressure magnitudes than those of untripped cases, of which the increment is up to 21 times the freestream static pressure for the farthest downstream transducer in the shock tunnel. The effects of trips are related to the streamwise vortexes in wake flows, in which interactions between external separations modify the separated flow patterns and enhance the sustainment of the forebody boundary layers to backpressure. Flow processes causing increments of oscillatory frequencies and pressure magnitudes are analyzed, while the flow mechanisms dominating the processes still need to be clarified in the future.

Scaling of interaction lengths for hypersonic shock wave/turbulent boundary layer interactions

The interaction length induced by Shock Wave/Turbulent Boundary-Layer Interactions(SWTBLIs)in the hypersonic flow was investigated using a scaling analysis,in which the interaction length normalized by the displacement thickness of boundary layer was correlated with a corrected non-dimensional separation criterion across the interaction after accounting for the wall temperature effects.A large number of hypersonic SWTBLIs were compiled to examine the scaling analysis over a wide range of Mach numbers,Reynolds numbers,and wall temperatures.The results indicate that the hypersonic SWTBLIs with low Reynolds numbers collapse on the supersonic SWTBLIs,while the hypersonic cases with high Reynolds numbers show a more rapid growth of the interaction length than that with low Reynolds numbers.Thus,two scaling relationships are identified according to different Reynolds numbers for the hypersonic SWTBLIs.The scaling analysis provides valuable guidelines for engineering prediction of the interaction length,and thus,enriches the knowledge of hypersonic SWTBLIs.

A PRIORI ERROR ESTIMATES OF A COMBINED MIXED FINITE ELEMENT AND DISCONTINUOUS GALERKIN METHOD FOR COMPRESSIBLE MISCIBLE DISPLACEMENT WITH MOLECULAR DIFFUSION AND DISPERSION

A combined approximation for a kind of compressible miscible displacement problems including molecular diffusion and dispersion in porous media is studied. Mixed finite el- ement method is applied to the ftow equation, and the transport one is solved by the symmetric interior penalty discontinuous Galerkin method （SIPG）. To avoid the inconve- nience of the cut-off operator in [3, 21], some induction hypotheses different from the ones in [6] are used. Based on interpolation projection properties, a priori hp error estimates are obtained. Comparing with the existing error analysis that only deals with the diffusion case, the current work is more complicated and more significant.

A POSTERIORI ERROR ANALYSIS FOR A FULLY DISCRETE DISCONTINUOUS GALERKIN APPROXIMATION TO A KIND OF REACTIVE TRANSPORT PROBLEMS

In order to obtain an expected numerical solution, a fully discrete discontinuous Galerkin method is applied to a kind of reactive transport problems in two dimension. That is to say, the space variable is discretized with the symmetric interior penalty Calerkin method （SIPG）, and the time variable is done with the backward Euler method. Making use of the duality technique, hp approximation properties and the interpolation theory, a residual-type a posteriori error estimation is achieved, which can be used for adaptivity. Compared with the analyses of semi-discretization, the current presentation is more challenging and more significant.

Planar laser scattering visualization of streamwise vortex pairs in a Mach 6 flow

A series of cross-sectional flow fields of Counterrotating Vortex Pairs(CVPs) generated by a large-scale ramp vortex generator is observed using an ice-cluster-based Planar Laser Scattering(PLS) method in a shock tunnel with a nominal flow Mach number of 6. Combined with a numerical simulation, two streamwise CVPs with opposite rotating directions are identified in the wake flow of the vortex generator with an absence of a boundary layer, namely, a Primary CVP(PCVP) and a Secondary CVP(SCVP). The wake flow is divided into two stages with different features of the PCVP and SCVP. In Stage Ⅰ, the PCVP and SCVP gradually mature, and the flow is relatively stable. In Stage Ⅱ, the PCVP and SCVP depart from each other, and the flow becomes unstable. The profiles of the transverse velocity in the spanwise symmetry plane induced by the PCVP and SCVP do not obey the scaling law of CVPs immersed in the boundary layer. A new scaling law is proposed, in which the transverse distances between adjacent saddle points in the cross-sectional flow field are used as the characteristic lengths for the PCVP and SCVP. After this new scaling procedure, the profiles of transverse velocity induced by the PCVP and SCVP at different streamwise locations collapse well. Moreover, the PLS images show that the mixing between the CVPs and the outside high-momentum flow becomes evident at approximately 5.5 times the height of the vortex generator, which is earlier than that immersed in the boundary layer. These findings enrich the knowledge of CVPs in the hypersonic regime, especially in the absence of the boundary layer.

Design, fabrication, and testing of a maneuverable underwater vehicle with a hybrid propulsor

Rapidity and agility are equally important to unmanned underwater vehicles(UUVs).In this study we developed a UUV equipped with a hybrid propulsor which consists of a screw propeller and four bio-inspired flippers.The bionic flippers rely on their flapping motion to generate both thrust and lateral forces,and the screw propeller provides additional thrust for fast cruise.The maneuverability is greatly improved while the capability of sailing fast is maintained.For the typical sailing requests,the flapping motions of the flippers were designed meticulously,and a control algorithm based on central pattern generators(CPGs)was built to produce rhythmic locomotor signals considering the motion periodicity.Simultaneously,a feedback control method was merged to correct the deviation of the course.A compact concentric-shafts transmission mechanism was employed to overcome the inadequacy of the inside space,and the vehicle was built.Finally,the sailing and maneuvering performance were tested.It was demonstrated that,the UUV’s overall sailing performance was enhanced significantly due to the combination of the flapping flippers and the screw propeller.The hybrid-propulsor vehicle is capable of sailing in multiplicate environments.

Deformation process of a shocked drop-in-liquid

A mixed flow of two immiscible liquids may form drops of one liquid in the other. Deformation and breakup of drops occur when there is sufficient hydrodynamic or surface forces from the ambient liquid; such deformation and breakup of drops is a common phenomenon in various engineering applications, such as oil-water flow in the petroleum recovery industry [1, 2], stirred dispersions in the chemical industry [3,4], and melted metal and cooling liquid interactions in the nuclear industry [5, 6]. A typical simplified model for the mechanism study is the behaviours of a single drop against its surrounding liquid.

A Posteriori Error Estimates of a Combined Mixed Finite Element and Discontinuous Galerkin Method for a Kind of Compressible Miscible Displacement Problems

Akind of compressiblemiscible displacement problemswhich includemolecular diffusion and dispersion in porous media are investigated.The mixed finite element method is applied to the flow equation,and the transport one is solved by the symmetric interior penalty discontinuous Galerkin method.Based on a duality argument,employing projection estimates and approximation properties,a posteriori residual-type hp error estimates for the coupled system are presented,which is often used for guiding adaptivity.Comparing with the error analysis carried out by Yang(Int.J.Numer.Meth.Fluids,65(7)(2011),pp.781-797),the current work is more complicated and challenging.

Numerical Investigation of Supersonic Channel Flow with Oscillatory Backpressures

The investigation of supersonic channel flow with periodic oscillatory backpressures at the outlet of the channel was performed using large-eddy simulation for the inlet free-stream Mach number 4 and the Reynolds number approximately 5.2104 based on the height of the channel.Results have been validated carefully against our experimental data.Three typical backpressures are considered for constant backpressure and both periodic oscillatory backpressures with low and high frequency.The oscillatory backpressure can obviously influence the flow features occurring up to the middle region of the channel for the low frequency case and the downstream region for the high frequency case.Obvious differences of phase-averaged quantities at different phases are observed for the low frequency backpressure while the differences are relatively small for the high frequency backpressure.The spectral analysis reveals that the flow field experiences a periodic-like evolution of flow structures including shocks and vortices for the low frequency backpressure,resulting in the enhancement of turbulence fluctuations due to the complicated interaction of shocks and vortices.

Highly efficient enzymolysis and fermentation of corn stalk into L-lactic acid by enzyme-bacteria friendly ionic liquid pretreatment

Ionic liquids(ILs)have been widely used in the pretreatment of biomass.However,the effects of residual ILs on the enzymolysis and fermentation of biomass are still unknown.Therefore,a large quantity of water-washing is usually followed after biomass pretreatment to eliminate the inhibition of residual ILs on subsequent hydrolysis and fermentation steps.In this work,the effect of choline glycine([Ch][Gly])concentration on the activity of cellulase and Bacillus sp.strain P38 was systematically investigated to explore the impacts of residual ILs on enzymolysis and fermentation.The results confirmed that the activities of them were almost not inhibited in low concentrations(less than 0.5 wt%)of[Ch][Gly].Under optimal pretreatment conditions,the maximum cellulose digestibility was 99.23%.Enzymatic hydrolysate was suitable for L-lactic acid fermentation without appreciable inhibition,and the highest sugar-acid conversion rate of 96.33%was obtained by simplified detoxification.This work provides an economic route to produce fermentable sugar and L-lactic acid,which shows an industrial application prospect in lignocellulosic biorefinery.