Class-Shape Transformation Method Research Articles

An Improved Multi-Objective Particle Swarm Optimization Method for Rotor Airfoil Design

In this study, a multi-objective aerodynamic optimization is performed on the rotor airfoil via an improved MOPSO (multi-objective particle swarm optimization) method. A database of rotor airfoils containing both geometric and aerodynamic parameters is established, where the geometric parameters are obtained via the CST (class shape transformation) method and the aerodynamic parameters are obtained via CFD (computational fluid dynamics) simulations. On the basis of the database, a DBN (deep belief network) surrogate model is proposed and trained to accurately predict the aerodynamic parameters of the rotor airfoils. In order to improve the convergence rate and global searching ability of the standard MOPSO algorithm, an improved MOPSO framework is established. By embedding the DBN surrogate model into the improved MOPSO framework, multi-objective and multi-constraint aerodynamic optimization for the rotor airfoil is performed. Finally, the aerodynamic performance of the optimized rotor airfoil is validated through CFD simulations. The results indicate that the aerodynamic performance of the optimized rotor airfoil is improved dramatically compared with the baseline rotor airfoil.

Rapid Parametric CAx Tools for Modelling Morphing Wings of Micro Air Vehicles (MAVs)

This paper shows a series of tools that help in the research of morphing micro air vehicles (MAVs). These tools are aimed at generating parametric CAD models of wings in a few seconds that can be used in aerodynamic studies, either via CFD directly using the model obtained or via wind tunnel through rapid prototyping with 3D printers. It also facilitates the analysis of morphing wings by allowing for the continuous parametric deformation of the airfoils and the wing geometry. In addition, one of the tools greatly simplifies the purely experimental design of this type of vehicle, allowing the transfer of experimental measurements to the computer, generating virtual models with the same deformation as the physical model. This software has two fundamental parts. The first one is the parameterization of the airfoils, for which the CST (Class-Shape Transformation) method will be used. CST coefficients can be modified according to the actuator variable that changes the wing geometry. The second part is the generation of a three-dimensional parametric model of the wing. We used OpenCASCADE technology in its Python version called PythonOCC, which enables the generation of geometries with good surface quality for typical and non-standard wing shapes. Finally, the use of this software for the study of a morphing aircraft will be shown, as well as improvements that could be incorporated in the future to increase its capabilities for the design and analysis of MAVs.

Geometric Characteristics of Flapping Foils for Enhanced Propulsive Efficiency

AbstractThe shape of a foil undergoing a combined pitching heaving motion is critical to its design in applications that demand high efficiency and thrust. This study focuses on understanding of how the shape of a foil affects its propulsive performance. We perform two-dimensional numerical simulations of fluid flows around a flapping foil for different governing parameters in the range of biological swimmers and bio-inspired underwater vehicles. By varying the foil shape using a class-shape transformation method, we investigate a broad range of foil-like shapes. In the study, we also show consistent results with previous studies that a thicker leading-edge and sharper trailing-edge makes for a more efficient foil shape undergoing a flapping motion. In addition, we explain that the performance of the foil is highly sensitive to its shape, specifically the thickness of the foil between the 18th and 50th percent along the chord of the foil. Moreover, we elucidate the flow mechanisms behind variations in performance metrics, particularly focused on constructive interference between the vortices generated at the leading-edge with the trailing-edge vortex, as well as the pressure field differences that lead to higher power consumption in less efficient foil shapes.

Numerical investigation and optimization for interior duct shape of ducted tail rotor

In order to improve the aerodynamic performance of the ducted tail rotor, parametric investigations and optimization of the interior duct surface are performed based on the Computational Fluid Dynamics (CFD) method. Firstly, to predict the aerodynamic characteristics of the ducted tail rotor with high precision and efficiency, the Reynolds-Averaged Navier-Stokes (RANS) solver coupled with body-fitted mesh around rotor blade is established based on the rotating reference frame. Then, novel parametric researches on the aerodynamic characteristics of the ducted tail rotor are conducted with different lip radii, transition section lengths, and duct outlet areas respectively, and the flow separation mechanism on the different interior duct surfaces are obtained. Finally, a new curve lip shape parameterized by the Class Shape Transformation method is employed to replace the conventional circular lip, besides, the transition length and the outlet area which have great influences on the flow separation phenomenon are combined to conduct the optimization of the interior duct surface. Attribute to the suppression of the flow separation, the required power and the FM of the optimized ducted tail rotor show a maximum decrement of 2.49% and a maximum increment of 2.44% with respect to the baseline SA365N1 ducted tail rotor respectively.

Heat Transfer Improvement in Automotive Brake Disks Via Shape Optimization of Cooling Vanes Using Improved TPSO Algorithm Coupled With Artificial Neural Network

One important safety issue in automotive industry is the efficient cooling of brake system. This research work aims to introduce an optimized cooling vane geometry to enhance heat removal performance of ventilated brake disks. The novel idea of using airfoil vanes is followed as the basis of this investigation (Nejat et al., 2011, “Heat Transfer Enhancement in Ventilated Brake Disk Using Double Airfoil Vanes,” ASME J. Therm. Sci. Eng. Appl., 3(4), p. 045001). In order to perform the optimization technique efficiently, an integrated shape optimization process is designed. According to the aerodynamic and heat transfer considerations, first an appropriate airfoil is selected as the base profile to be optimized. For the shape modification purpose, a curve parameterization method named class shape transformation (CST) is utilized. The control parameters defined in CST method are then established as the geometrical design variables of an improved territorial particle swarm optimization (TPSO) algorithm. In order to overcome the potential bottleneck of high computational cost associated with the required computational fluid dynamics (CFD)-based function evaluations, TPSO algorithm is coupled with a predictive artificial neural networks (ANN), well trained with an input dataset designed based on the Taguchi method. The obtained profile shows an evident convective heat dissipation improvement accomplished mainly via airflow acceleration over the vanes, avoiding early flow detachment and adjusting the flow separation region at the rear part of the suction sides. The results also reveal the approaches by which such a superior performance is achieved by means of the modified surface curvatures.

Integrated analysis of aerodynamic/stealth characteristics of blended-wing-body lifting vehicle

In this paper, a blended-wing-body lifting vehicle is designed, with the cross section described by Class/Shape transformation method (CST), the outline controlled by an exponential function, and tail regulated by B-spline curve. Rapid estimation procedures of aerodynamic based on plane method and of radar cross section (RCS) based on physical optics are developed and validated. A frame of integrated design and analysis of aerodynamic and stealth characteristics is constructed and applied to parameter sensitivity analysis. The results show that the parameters that affect the aerodynamic differ from those of RCS, which means the vehicle could be good at both aerodynamic and stealth, and the study followed should be focused on it.

Three-Dimensional CST Parameterization Method Applied in Aircraft Aeroelastic Analysis

Class/shape transformation (CST) method has advantages of adjustable design variables and powerful parametric geometric shape design ability and has been widely used in aerodynamic design and optimization processes. Three-dimensional CST is an extension for complex aircraft and can generate diverse three-dimensional aircraft and the corresponding mesh automatically and quickly. This paper proposes a parametric structural modeling method based on gridding feature extraction from the aerodynamic mesh generated by the three-dimensional CST method. This novel method can create parametric structural model for fuselage and wing and keep the coordination between the aerodynamic mesh and the structural mesh. Based on the generated aerodynamic model and structural model, an automatic process for aeroelastic modeling and solving is presented with the panel method for aerodynamic solver and NASTRAN for structural solver. A reusable launch vehicle (RLV) is used to illustrate the process for aeroelastic modeling and solving. The result shows that this method can generate aeroelastic model for diverse complex three-dimensional aircraft automatically and reduce the difficulty of aeroelastic analysis dramatically. It provides an effective approach to make use of the aeroelastic analysis at the conceptual design phase for modern aircraft.

Supercritical natural laminar flow airfoil optimization for regional aircraft wing design

An optimization design method of supercritical natural laminar flow airfoil based on Genetic Algorithm and Computational Fluid Dynamics is tested in this paper. Class Shape Transformation method is adopted as geometry parameterization method. Constraints on pressure distribution are applied to gain appropriate flow field in addition to the L/D performance. A fixed transition computation method is used in the optimization process to save computation time while giving the reasonable friction drag estimation and predicting the influence of the laminar boundary layer on airfoil performances. Specified favorable pressure gradient constraints are used to guarantee the expected laminar length. Objective of optimization is set to weaken the shock wave and minimize the pressure drag. Such a simplified NLF optimization process is verified by natural transition computation. The optimal setting of the favorable pressure gradient constraint, which is important for the trade-off between drag reduction and laminar stability, is then studied via numerical investigation. Results show that the airfoil optimized by constraining a favorable pressure gradient larger than 0.2 is good for both cruise efficiency and robustness. A natural laminar wing is then designed based on the optimized airfoil. Numerical verifications show that the wing has good natural laminar performance and low speed behavior.

Supersonic Bi-Directional Flying Wing Wave Drag Optimization Based on Alternative Form of CST Method

Bi-directional Flying Wing (BFW) is a new supersonic civil transport shape concept that aims to meet the conflict requirements of high speed cruise and low speed take-off/landing missions. In this paper the Class-Shape-Transformation (CST) shape parameterization method is modified to represent the BFW shape, and new basis functions suitable for the BFW airfoil representation are constructed. The Far-field Composite Element (FCE) wave drag optimization is performed on both the flat bottom and symmetric BFW configurations, and the drag reduction effects and result precision are surveyed. It is suggested that significant wave drag reduction can be achieved by the FCE optimization for both the flat bottom and the symmetric BFW configurations. The wave drag coefficients with sufficient precision can be obtained in the FCE optimization of the symmetric configuration; while the FCE optimization results of the flat bottom one are not accurate enough.