Aerodynamic Design Concepts Research Articles

D-SEND#2の制御系設計

This paper is concerned with flight controller design of D-SEND#2. D-SEND is a project to demonstrate a low sonic boom aerodynamic design concept. In the #2 part of this project, an unpowered test vehicle is lifted to an altitude of 30km by a balloon from which it then separates. After the separation, the vehicle's on-board flight control computer selects a target Boom Measurement System (BMS) according to the separation point. The vehicle then autonomously flies to the selected BMS and establishes prescribed sonic boom measurement flight conditions. The design of the GNC system for D-SEND#2 project is exceptionally challenging since 1) there is no nominal trajectory, 2) there is only limited control available to meet various requirements, 3) the flight envelope is quite wide, and 4) the development time is short. Dynamic inversion method and time-scale separation technique are applied to deal with these problems, and a systematic controller design procedure is presented. The controller is designed with this procedure and evaluated through linear analysis and Monte-Carlo simulations which shows it has sufficient performance and safety margines. This controller design method is confirmed to be a practical method for UAVs.

Aerodynamic Characteristics of Supercritical Outlet Guide Vanes at Low Reynolds Number Conditions

As a part of an innovative aerodynamic design concept for a single stage low pressure turbine, a high turning outlet guide vane is required to remove the swirl from the hot gas. The airfoil of the vane is a highly loaded compressor airfoil that has to operate at very low Reynolds numbers (Re∼120,000). Recently published numerical design studies and experimental analysis on alternatively designed airfoils showed that blade profiles with an extreme front loaded pressure distribution are advantageous for low Reynolds number conditions. The advantage even holds true for an increased inlet Mach number at which the peak Mach number on the airfoils reaches and exceeds the critical conditions (Mss>1.0). This paper discusses the effect of the inlet Mach number and Reynolds number on the cascade performance for both a controlled diffusion airfoil (CDA) (called baseline) and a numerically optimized front loaded airfoil. The results show that it is advantageous to design the profile with a fairly steep pressure gradient immediately at the front part in order to promote early transition or to prevent too large laminar—even shock induced—separations with the risk of a bubble burst. Profile Mach number distributions and wake traverse data are presented for design and off-design conditions. The discussion of Mach number distributions and boundary layer behavior is supported by numerical results obtained from the blade-to-blade flow solver MISES.

A Study of Advanced High-Loaded Transonic Turbine Airfoils

The development of high-performance turbine airfoils has been investigated under the condition of a supersonic exit Mach number. In order to obtain a new aerodynamic design concept for a high-loaded turbine rotor blade, we employed an evolutionary algorithm for numerical optimization. The target of the optimization method, which is called evolutionary strategy (ES), was the minimization of the total pressure loss and the deviation angle. The optimization process includes the representation of the airfoil geometry, the generation of the grid for a blade-to-blade computational fluid dynamics analysis, and a two-dimensional Navier-Stokes solver with a low-Re k-ε turbulence model in order to evaluate the performance. Some interesting aspects, for example, a double shock system, an early transition, and a redistribution of aerodynamic loading on blade surface, observed in the optimized airfoil, are discussed. The increased performance of the optimized blade has been confirmed by detailed experimental investigation, using conventional probes, hotfilms, and L2F system.

Design concept of a high-altitude long-endurance unmanned aerial vehicle

This paper presents a conceptual project of a high-altitude long-endurance unmanned aerial vehicle. It describes a number of historical, current and prospective HALE aircraft and considers existing four serious obstacles, to overcome them can mean the successful building of HALE aircraft. Among these obstacles there are very special aerodynamic (low Reynolds numbers together with transonic speeds), very light structures usually of high aspect ratio, propulsion technology (usually propeller driven by turbocharged piston engines) and flight control system (usually combining the best features of preprogrammed and hand-flown modes). Four aerodynamic design concepts are presented and their performances are compared. Among them is a biplane, considered mainly because of its moderate wing span, which can be obtained for a relatively big wing area and a high effective wing aspect ratio, a relatively stiff wing structure, and lower induced drag being possible to be obtained at the same lift and wing area as for the equivalent monoplane. It is shown that an attentively designed biplane can be efficient aerodynamically for high altitude patrol missions having almost the same endurance, using the same fuel to reach a service ceiling and having the take-off mass (and the payload) considerably bigger than a corresponding, equivalent monoplane. The paper is completed with selected considerations about dynamic stability.