Yong-Liang Yu

A Numerical Simulation of a Fishlike Body’s Self‐propelled C‐start

This paper presents a numerical method to deal with a two‐dimensional deformable fishlike body’s large deformation self‐propelled swimming. Overset grids are employed to discretize the flow domain around the large deforming body which is simulated by a foil. The kinematics, energetics and the flow structures of a typical C‐start are predicted by a coupling solution of the two‐dimensional incompressible fluid dynamics and the deforming body dynamics. As a typical practice, the foil performs a C‐start‐like motion in stationary water based on the prescribed deforming mode. It is found that the locomotion of the foil is similar to a real fish’s C‐start and the hydrodynamic efficiency of this C‐start model is about 29% which is close to the value calculated by the previous theoretical estimation. Particularly, a structure of three significant concentrated vortices is discovered in the wake.

Aerodynamic mechanism of forces generated by twisting model-wing in bat flapping flight

The aerodynamic mechanism of the bat wing membrane along the lateral border of its body is studied. The twist-morphing that alters the angle of attack (AOA) along the span-wise direction is observed widely during bat flapping flight. An assumption is made that the linearly distributed AOA is along the span-wise direction. The plate with the aspect ratio of 3 is used to model a bat wing. A three-dimensional (3D) unsteady panel method is used to predict the aerodynamic forces generated by the flapping plate with leading edge separation. It is found that, relative to the rigid wing flapping, twisting motion can increase the averaged lift by as much as 25% and produce thrust instead of drag. Furthermore, the aerodynamic forces (lift/drag) generated by a twisting plate-wing are similar to those of a pitching rigid-wing, meaning that the twisting in bat flight has the same function as the supination/pronation motion in insect flight.

Aerodynamics and mechanisms of elementary morphing models for flapping wing in forward flight of bat

The large active wing deformation is a significant way to generate high aerodynamic forces required in bat flapping flight. Besides the twisting, the elementary morphing models of a bat wing are proposed, such as wing-bending in the spanwise direction, wing-cambering in the chordwise direction, and wing area-changing. A plate of aspect ratio 3 is used to model a bat wing and a three dimensional unsteady panel method is applied to predict the aerodynamic forces. It is found that the cambering model has a great positive influence on the lift, followed by area-changing model and then the bending model. The further study indicates that the vortex control is a main mechanism to produce high aerodynamic forces, and the mechanisms for the aerodynamic force enhancement are the asymmetry of the cambered wing and the amplifier effects of wing area-changing and wing bending. The lift and thrust are mainly generated during the downstroke and almost negligible forces during the upstroke by the integrated morphing model-wing.

Nonlinear Shear and Heat Transfer in Hypersonic Rarefied Flows Past Flat Plates

This paper is a theoretical modeling study of the nonlinear transport of momentum and energy in a hypersonic rarefied flow past a sharp leading-edge flat plate at zero angle of attack. A characteristic parameter Vrx is introduced to describe the non-Newtonian shear and non-Fourier heat transfer features in the near-continuum flow regime via approximate analyses on the corresponding terms from the Burnett equation. Modified formulas based on Vrx are proposed to quantitatively predict the skin friction and heat flux along the plate, and the Reynolds analogy is proved to still be valid in the near-continuum flow regime. The physical meaning of Vrx and the flow mechanism are discussed. The direct simulation Monte Carlo method is also employed to validate the analytical results and to show the existence of a general analogy between the skin friction and heat flux in the whole flow regime from the continuum through the transition to the free molecular flow limit.

General Reynolds Analogy for Blunt-Nosed Bodies in Hypersonic Flows

In this paper, the relation between skin friction and heat transfer along windward sides of blunt-nosed bodies in hypersonic flows is investigated. The self-similar boundary layer analysis is accepted to figure out the distribution of the ratio of skin friction to heat transfer coefficients along the wall. It is theoretically obtained that the ratio depends linearly on the local slope angle of the wall surface, and an explicit analogy expression is presented for circular cylinders, although the linear distribution is also found for other nose shapes and even in gas flows with chemical reactions. Furthermore, based on the theoretical modelling of the second order shear and heat transfer terms in Burnett equations, a modified analogy is derived in the near continuum regime by considering the rarefied gas effects. And a bridge function is also constructed to describe the nonlinear analogy in the transition flow regime. At last, the direct simulation Monte Carlo method is used to validate the theoretical results. The general analogy, beyond the classical Reynolds analogy, is applicable to both flat plates and blunt-nosed bodies, in either continuous or rarefied hypersonic flows.

Study of the post separation pH adjustment by a microchip for the analysis of aminoglycoside antibiotics

Recently, we developed a simple microchip to simultaneously accommodate acidic conditions for the separation and alkaline conditions for the electrochemical detection of aminoglycoside antibiotics [Electrophoresis, DOI: 10.1002/elps.201200309]. With two branch channels connected near the end of the separation channel, the alkaline solution was hydrostatically introduced into a Z-shaped mixing channel and combined with the acidic stream from the separation channel. As a result, the pH of the mixed solution was adjusted to the desired value for the electrochemical detection of aminoglycoside antibiotics. In this manuscript, the principle and related parameters of the pH adjustment on the microchip were investigated both in theory and practice. With the guidance of the principle of the post separation pH adjustment, we applied the functional microchip to the analysis of six aminoglycoside antibiotics in a biological sample with satisfactory analytical performances. Specifically, these compounds were electrophoretically separated in 5 mM sodium acetate (pH = 4) and 0.6 mM CTAB, and through the post separation pH adjustment, electrochemically detected in alkaline conditions (pH > 12) at a Cu–Sn–Cr alloy electrode. Additionally, this microchip may provide a possible use for the post separation reagent addition for enzyme-assisted electrochemical detection.

Morphing Models of a Bat Wing in Flapping Flight

Kinematic models, which contain flapping and deformations, of a bat flapping wing when it flies at medium speeds are presented in the study. The deformations include cambering - morphing in the chordwise direction, bending - morphing in the spanwise direction and twisting respecting angles of attack (AOA) varying along the length of the wing. In the study, we assumed a circular-arc-shaped deformation when cambering or bending occurs, and introduced controlling parameters for each morphing. Then we showed the expressions of the controlling parameters varying with time at the bat flight speed of 3m/s according to the data provided by a literature, and verified the reasonability of the assumptions at last.

Preliminary Modeling of the Fluid-Structure Interaction on a Deformable Insect Wing in Flapping

Insect wings are considered as highly functional and largely optimized mechanical constructions. They can deform passively in flapping, corresponding to external aerodynamic loading, wing’s structure and material properties, which is a complicated Fluid-Structure Interaction course. In this paper, a viscoelastic constitutive relation model of the dragonfly wing was established firstly, and then the FSI problem — the periodical deformation in wing flapping was primarily explored.