Supercritical fluid properties are implemented in a one-dimensional counterflow flame simulation code using the Soave-Redlich-Kwong equation of state and modifying the transport properties for high-pressure, low-temperature conditions. Examination of a GH2/LOX diffusion flame at supercritical pressure reveals an extremely fine structure at the edge of the oxygen diffusion layer, indicating that a DNS-like approach to simulation of such flames is not practical in the near term, and flame modeling must be used. To investigate flamelet table construction, we compare simulations that use supercritical fluid and standard temperature and pressure (STP) gas properties. Both types of simulations are shown to produce almost identical flame structures when we parameterize the flame with the scalar dissipation rate at its stoichiometric position. The results show that the use of STP gas property simulation is expected to be an effective means of greatly reducing the computational cost of constructing flamelet tables at supercritical pressures.
Collision risk modeling is a methodology to estimate the risk of aircraft collisions under given route spacing/separation minima. Both pre-implementation risk estimation and continuous long-term risk monitoring are encouraged by the International Civil Aviation Organization. Collision risk modeling is an often-used methodology for that purpose. Mixture distribution models of Gaussian and Laplace distributions are often used for the modeling of lateral deviations of aircraft from the center line of air routes. We developed an iterative Bayesian parameter estimation algorithm of the mixture distributions which is classified as a variational Bayesian method. It is a heuristic algorithm which estimates the model parameters from observation data. We select the appropriate family of prior distributions so that the posterior distributions have the same form of the prior distributions. This feature enables iterative application of the algorithm. The algorithm also enables interval estimation of statistics such as lateral overlap probabilities, which is a key parameter of the collision risk model of route spacing. It can be used for long-term monitoring of lateral deviation of aircraft. We also applied the algorithm to the data of lateral deviations observed in Japanese oceanic airspace. The application example showed that our algorithm can be applied for real data.
Using multiple control surfaces to actively suppress nonlinear transonic aeroelastic responses is a promising technology. A general method for designing a multiple-input multiple-output (MIMO) active aeroelastic control law is proposed. The Volterra series is applied to construct a high-fidelity reduced-order aeroservoelastic plant model suitable for transonic flow. The static output feedback method is also used to design a MIMO control law. The effectiveness of the proposed method to design the MIMO active aeroelastic control law is demonstrated by the Goland+ wing model with four control surfaces. The simulation results show that the MIMO active control law suppresses the transonic unstable aeroelastic responses of the Goland wing successfully with good control performance.
Arrival time control in a continuous descent operation (CDO) and its application to arrival traffic control are discussed. Through numerical simulations, the feasibility of the arrival time extension and reduction while maintaining the idle thrust during the continuous descent trajectory is presented. The extensible and reducible time of a CDO trajectory are also numerically analyzed. They are uniquely determined by the aircraft speed, altitude and distance from the runway. The CDO trajectory that potentially has the maximum extensible and reducible time is also proposed, which is expected to cancel the deviation of arrival time from that scheduled. A set of numerical traffic simulations proves the effectiveness of the proposed traffic control strategy. It is concluded that CDO using the proposed traffic control strategy is able to achieve delay-free air traffic with enhanced arrival time predictability. A noteworthy numerical result is also obtained showing that a slower trajectory for a larger reducible time can achieve a faster arrival time on average than the fastest trajectory with no reducible time.
The variation in aerodynamic forces acting on an ornithopter and an airplane with one or two propellers, which generate the same thrust under no gust wind, is compared when they encounter a gust of wind. The consumed power, or the period of one cycle of flapping motion and that of one rotation of propeller(s), remains constant before and after they encounter a wind gust. The following results are obtained under both conditions. The variation in aerodynamic forces caused by vertical and frontal wind gusts of an ornithopter are a little smaller than that of an airplane with one or two propellers. The difference in variation in aerodynamic forces caused by a side wind gust between them are often larger than that caused by vertical and frontal wind gusts. The variation in aerodynamic forces caused by a side wind gust of the former is smaller than that of the latter when the reciprocal of the advance ratio of the propeller and the flapping amplitude of the ornithopter are small.
The wind environment at an airport is affected by terrain features. In Japan, Shonai Airport is known to frequently have wind shear over the runway due to the turbulence induced by the neighboring hills in winter. In this study, large eddy simulation (LES) is performed to investigate the turbulence around Shonai Airport. The initial and boundary conditions are given according to the weather prediction data by the Japan Meteorological Agency non-hydrostatic model (JMANHM). These data are downscaled and transferred to LES domains, which consider actual terrain features as the boundary conditions on the ground, using the two-way nesting method. The present simulations indicate that terrain features may have a significant influence on the turbulence appearing in flight paths; i.e., aircraft safety may depend on wind direction. In addition, it is shown that the present simulation method can predict the turbulence induced by terrain features based on good agreement of results with the turbulence actually observed using a Doppler radar.
A parametric study of vortex generators (VGs) on the transonic infinite-wing with two types of airfoil is performed using computational fluid dynamics to identify the effects of five parameters: height, aspect ratio, incidence angle, spacing and chord location, on the aerodynamic characteristics. First, an SC(2)-0518 airfoil with large thickness ratio and leading-edge radius is employed. The VG spacing significantly affects the shock wave location. If the spacing is narrow, the shock wave moves downstream, which increases the lift coefficient at a high angle of attack. In contrast, broad spacing suppresses the fluctuation of the pitching moment coefficients. This difference is caused by the interactions among vortices. The VG height changes the drag coefficients and is correlated with the VG spacing. The other airfoil considered is a cross-section airfoil of a NASA common research model with small thickness ratio and leading-edge radius. The spacing effect with this airfoil is almost the same as that of the SC(2)-0518 airfoil. The VG location has little influence, but the VG located more upstream would be better. In addition, an appropriate incidence angle and aspect ratio exist for generating the vortex efficiently.
In order to understand the unusual flutter phenomenon observed in experimental transonic flow for a high-aspect-ratio forward-swept wing, numerical simulations are conducted using a 3D Navier-Stokes code. The simulations confirm that the flutter is a single-degree-of-freedom flutter of the first bending mode in which shock-induced flow separation plays a dominant role. The simulations also clarify the detailed effects of Mach number and dynamic pressure (particularly the mass ratio) on this type of flutter.
Recently, composite materials have been introduced to commercial aircraft primary structures for the purpose of increased weight savings, reduction in corrosion, enhanced fatigue life and improved performance. However, repairing these primary structures can be very challenging to operators. A brief description is given about repairing aircraft non-primary composite structures. More importantly, however, this paper discusses the current research carried out by major aerospace companies and their academic partners to develop reliable methods, tools and equipment for repairing aircraft primary composite structures. These new technologies aim to give the use of composite materials on ``next-generation'' commercial aircraft primary structures a more prominent advantage by addressing the issue of recurring costs due to maintenance.