Yuguang Bai

Numerical aerodynamic simulations of a NACA airfoil using CFD with block-iterative coupling and turbulence modelling

Numerical aerodynamic simulations are presented for a National Advisory Committee for Aeronautics (NACA) airfoil that is stationary and pitching at high Reynolds numbers. A new improved CFD method based on block-iterative coupling is used with a computational scheme for fluid-structure interaction, in which a form of two-equation RANS turbulence model is adopted. Firstly, basic simulations were performed using the proposed CFD method and turbulence model, which provides good prediction of the airfoil force coefficients and flutter derivatives compared with the well-known experimental measurement and analytical formulation. Then, extended airfoil flow simulations were carried out to examine the potentially significant effects on aeroelasticity from several influencing factors, including non-zero equilibrium angles of attack, increased forced vibration amplitudes and large Reynolds number. Both the basic and extended simulations reveal that using the proposed CFD method can provide effective assessment of aerodynamic and aeroelastic performance of airfoils even for operating conditions beyond those a laboratory test can approach, indicating the possibility of extending the methodology proposed for realistic aerodynamic and aeroelastic prediction of 3D full-scale aircraft structures.

Numerical analysis of thermoacoustic characteristics of components inside a complex aircraft related to the coupling effect of high temperature and random vibration

Hypersonic aircraft always face bad flight environment related to the coupling effects of high temperature and random vibration. Numerical analysis of thermoacoustic characteristics of components inside such an aircraft is presented in this paper. An actual aircraft cabin composite structure including a heat resistant layer, an adiabatic layer and metal frameworks is modeled with the finite element mesh generation method. Transient heat conduction of the hypersonic flight aircraft is analyzed based on a block-iterative coupling method which can consider the atmosphere-aircraft interaction. Then the Von Karman turbulence spectrum is employed to define the random vibration environment of the present aircraft. The thermodynamic response of the system is solved by the pseudo-excitation method which can improve the computation efficiency greatly. Finally, thermoacoustic characteristic of the cavity inside the aircraft cabin is analyzed when the transient heat conduction and random vibration due to atmosphere turbulence are both included. A numerical method is proposed based on a structure-acoustic coupling method which can use acoustic equations to simulate the propagation of the acoustic wave in the flow. It can be found from the computed results that the change of the temperature influences both the thermodynamic characteristic of the aircraft cabin and thermoacoustic characteristic of the component inside the present aircraft significantly. So the coupling effects of high temperature and random vibration on thermoacoustic characteristic of a hypersonic flight aircraft cannot be neglected. The proposed numerical analysis method in this paper can be widely applied to numerical investigations of thermoacoustic systems inside hypersonic aircraft.

Experimental and numerical study of dynamic characteristic of a complex all-movable rudder system

Modal analysis and flutter computation of a complex tail cabin system including six all-movable rudders for hypersonic flight vehicle was studied in this paper. Recently, some complex all-movable rudder system has been applied to hypersonic flight vehicle. Many investigations were taken to analyse a single all-movable rudder, such as modal analysis, flutter analysis, aero-heating analysis, etc. But most of existing investigations emphasized on single rudder. In this paper, a complex tail cabin system including six all-movable rudders from the X-51A vehicle was investigated. Modal analysis was presented based on accurate finite element modelling and bending and twisting modes of the structure were computed. Ground vibration test was provided to confirm the accuracy of computation. Then flutter characteristic of this complex system was analysed based on doublet lattice method. With flight Mach number 3 and 4, flutter analysis relating to both symmetric mode and antisymmetric mode was presented. It can be found from the presented results of flutter analysis that there were obvious and non-negligible coupling vibration effects among rudders in such a complex rudder system. So flutter characteristic of hypersonic flight vehicle should be analysed based on the whole system modelling including all of rudders. This analysis process can play a significant role for the design and flight of hypersonic vehicle.

Aero-servo-elastic analysis of a hypersonic aircraft

Aero-servo-elastic analysis of a complex hypersonic aircraft is presented in this paper. A structure geometry was designed and built based on the X-43A vehicle. First, a three-dimensional structural finite element model was proposed with effective two-dimensional elements, which can obtain effective modal analysis results without useless local modes. Second, computational fluid dynamic (CFD) simulation was adopted to find aero-heating distribution of thermal mode via this structure. Aero-heating effect was included to study thermal-modal characteristics of the present structure. Influence due to material characteristic change and thermal stress was studied. After structural finite element analysis was completed, flutter of the present vehicle was investigated. Aero-servo-elastic analysis was then started from the definition of an aero-servo-elastic closed-loop system. In this system, the present aircraft is treated as flexible structure, in which the control sensor on the aircraft received not only rigid motion signal but also elastic vibration signal, and this signal can translate into the deflection signal to form aerodynamic control force through this aero-servo control system, and this force can continually influence aerodynamic force. One of the most important steps for this analysis was computation of unsteady aerodynamic force of the present structure, and the related process was developed based on an effective fitting method. Finally, bode diagrams of pitching, rolling and yawing were investigated, form which the law of aero-servo stability of the X-43A vehicle can be observed and analyzed. It can be found from the results of this paper that effective investigation of aero-servo-elastic characteristics of a complex hypersonic aircraft should be based on accurate structural finite element modeling, modal analysis and flutter analysis. The proposed method in this paper can provide effective analysis process for the design of controller for hypersonic aircraft.

Numerical Investigations of Aeroheating for Missile Slots

AbstractA hypersonic aeroheating numerical simulation method for the missile slot flow in the conditions of high temperature and thermochemical nonequilibrium is carried out. The finite-volume method for solving Navier-Stokes equation based on the second-order accuracy upwind scheme is employed in the multiply blocked structure grid solver. The solver includes Park’s two-temperature model and the air multispecies reaction model. The derivation of the total variation diminishing (TVD) formulation with second-order accuracy is implemented in order to improve the efficiency of the hypersonic aeroheating computations. From the comparison between the results of the presented numerical method and the existing experiment data, it can be concluded that the proposed method can provide encouraging computational accuracy.

Numerical Analysis of Active Cooling Structure of Engine Combustion Chamber

With the convective heat transfer theory, numerical analysis of fluid-solid-heat coupling is implemented for the engine combustion chamber cooling structure based on finite element method and computational fluid dynamic method, thus to obtain valuable simulation results. Different components of the mesh generation method used which have different influences on the computational results are thought over during this analysis process, including different grid type, grid density and boundary layer meshes. Moreover, MPI parallel technique is also used to resolve the computation demands. The temperature distributions of the key parts in the cooling structure are investigated, which can be used as a significant reference for the thermal protection design of the engine combustion chamber.

Numerical Analysis of a Heater with Conjugate Heat Transfer

This paper focuses on the influence of the conjugative heat transfer in a regenerative cooling structure. With proper numerical modelling by both finite element method and computational fluid dynamic method, the distribution of the temperature in the solid and coolant, the interfacial heat flux, and the stress state and the deformation of this cooling structure are obtained. These results show that the thermal equilibrium of the cooling structure can be achieved in a given flow condition. The present numerical method has significant benefits to solve the heat transfer between engine coolant and solid components.

Large Eddy Simulation of Vortex Shedding due to Forced Vibration of Cylinder

The classical work of Williamson [1] has identified different modes for vortex shedding under forced vibration of circular cylinders. His finding was rich and shows 2P, 2S, P+S, 2P+2S and even coalescence 2S and P+S modes when changing the wavelength and amplitude, actually providing a road map for later computational fluid dynamics practitioners to verify. But after almost twenty years very few has attempted to simulate a few cases to test the validity of the road map. With fluid-structure interaction simulation becoming increasingly important, the work to confirm the roadmap by CFD has been necessary. By a recently developed fully fluid structure interaction coupled solver and an innovative mesh control algorithm [2], the authors carried out systematic resolved large eddy simulation to compare the simulated flows with those on the Williamson roadmap. The finding of the authors shows all the above shedding modes, and surprisingly the coalescence modes too. The work gives the confidence on CFD for vortex induced vibration and can be used as a base for further investigation of fluid structure interaction of more complex geometries.

Flutter Derivative Identification using Turbulence Modelling

The 2D discrete vorticity method [1] and a vorticity-stream function formulation [2] were employed previously for aeroelastic study of prismatic structures. The two-equation k-? model was applied to simulate flows around stationary rectangular sections with different aspect ratios (B/D=Breadth/Depth) and satisfactory results have were reported [3]. The current work is to test applicability of two-equation RANS models in aeroelastic study of prismatic structures with streamlined or bluff sections. For this the k-ω model and the shear stress transportation (SST) model, a derivative of k- ω, both allowing low Reynolds number treatment of boundary layers, have been used on the NACA0012 and the B/D=4 rectangular sections pitching or translating in a sinusoidal way. The resultant unsteady aerodynamic pressure and friction on the model are integrated o give the transient drags, lifts and moments. Combined with the motion function specified for the model, the flutter derivatives (FD) of the sections are identified. The simulated FDs are compared with the Theodorsen theoretical values for the NACA-0012 section; with the Huston’s experimental results for the rectangular section. Good agreement is observed indicating the RANS turbulence models can be potentially applied to aeroelastic study of prismatic structures with streamlined or bluff cross sections.