Multipoint Aerodynamic Optimization Research Articles

The aerodynamic optimization of hypersonic vehicles with the proper-orthogonal-decomposition-based CST method

The flight performance of traditional hypersonic vehicles is limited to a specified incoming flow condition, their aerodynamic performance significantly deteriorates outside of the design condition. We construct a data-driven design framework for aerodynamic shape optimization of hypersonic vehicles, which can be used to improve the current flexibility of designing hypersonic vehicles based on the existing shockwave shape or flowfield. The framework uses a class function/shape function transformation to set parameters for the control sections of the vehicle, then the dimensions of the parameter matrix are reduced by using the proper orthogonal decomposition, and the surrogate model with improved expectations is combined to carry out the aerodynamic shape optimization of hypersonic vehicles. The hypersonic aerodynamic optimization design of NACA 0012 airfoil is conducted, which verifies the high efficiency of the optimization method. The single-point and multi-point aerodynamic optimization designs for the Hypersonic Technology Vehicle-2 (HTV-2) type are conducted. The correlation analysis to the fundamental modes of control sections and lift-to-drag ratio is performed, which verifies the accuracy of the design. Completed the single-point and multi-point optimized design of the entire vehicle considering 48 design variables and geometry restrictions with volume not less than 95% of the baseline. The single-point optimization increases the lift-to-drag ratio by 10.91%, and the multi-point optimization ensures that the aerodynamic performance is improved at all flight conditions and reduces the drag coefficient by 4.1% at the large angle of attack condition. The vehicle shape change rule that is controlled by the positively correlated and negatively correlated fundamental modes for the three control sections coincides with the optimized trend. The study demonstrated the effectiveness and practicality of the framework in the aerodynamic design of hypersonic vehicles.

Performance improvement of centrifugal compressors for fuel cell vehicles using the aerodynamic optimization and data mining methods

Centrifugal compressors are one of the most important auxiliary components in polymer electrolyte membrane fuel cell vehicles, which tend to operate at a narrow area with low specific speed. Here, the optimal design goals of centrifugal compressors are investigated on the basis of a lumped model for fuel cell systems. A three-dimensional multi-objective and multi-point aerodynamic optimization and data mining method for centrifugal compressors named ODM is presented via integrating a multi-island genetic algorithm, Reynolds-Average Navier-Stokes solver technique and self-organization map based data mining technique. Data mining indicates that compressor geometry would move to a small inlet diameter ratio and a narrow region of the outlet width ratio. Based on the optimization results, a centrifugal compressor for 100 kW fuel cell stack is manufactured. The experimental results show that the improvement of isentropic efficiency near low mass flow has been achieved, which indicates that the proposed ODM is effective in the performance improvement of centrifugal compressors for fuel cell vehicles.

DAFoam: An Open-Source Adjoint Framework for Multidisciplinary Design Optimization with OpenFOAM

The adjoint method is an efficient approach for computing derivatives that allow gradient-based optimization to handle systems parameterized with a large number of design variables. Despite this advantage, implementing the adjoint method for a partial-differential-equation-based primal solver is a time-consuming task. To lower the barrier for adjoint implementations, an object-oriented framework (DAFoam) is proposed to rapidly implement the discrete adjoint method for any steady-state OpenFOAM primal solver by adding or modifying only a few hundred lines of source code. In this paper, the DAFoam framework is introduced and the proposed object-oriented adjoint development process is illustrated. Using this strategy, the adjoint method is implemented for eight primal solvers, five turbulence models, and one radiation model in OpenFOAM. Excellent adjoint speed and scalability, with up to 10 million cells and 1536 CPU cores, and an average error in the adjoint derivatives of less than 0.1% are achieved. Finally, the implemented adjoint solvers and models are integrated into a gradient-based optimization framework, and four distinct design optimizations (multipoint aerodynamic optimization of a low-speed unmanned-aerial-vehicle wing, aerodynamic optimization of a transonic aircraft configuration, aerothermal optimization of a turbine internal cooling passage, and aerostructural optimization of a compressor rotor) are shown. DAFoam is available under an open-source license and is a powerful tool for the high-fidelity multidisciplinary design optimization of engineering systems, such as aircraft, ground vehicles, marine vessels, and turbomachinery.

Aerodynamic Optimization of Turbine Based Combined Cycle Nozzle

Abstract This paper aims at optimizing a Turbine Based Combined Cycle (TBCC) nozzle for upgrading its aerodynamic performance in multiple flight conditions. An in-house RANS solver called NSAWET is employed for aerodynamic evaluation. The optimizer is a differential evolution algorithm combined with a response surface. Firstly, a two-dimensional model of the initial TBCC nozzle system is investigated. The flow field of the nozzle contains complicated shockwave interactions that cause thrust loss. Then multi-point aerodynamic optimization of a two-dimensional ramjet nozzle is carried out, which objectives are to maximize the thrust coefficients at Mach numbers 2.5, 3.0 and 4.0. The objective functions are increased substantially at the first two Mach numbers after optimization, while slightly decreased at the last Mach number. The turbine flow path is built up based on the optimized profile and the performances in typical flight conditions are validated. Results demonstrate that both the ramjet and turbine nozzles are improved in most flight conditions.

Aerodynamic Design of the Supersonic Aircraft Wing-Shape and Wing-Twist Optimization

This paper builds an aerodynamic optimization design system by coupling the free form deformation parameterization technique, the dynamic mesh technique based on inverse distance weighting interpolation method and particle swarm optimization algorithm, Kriging surrogate model, with the computational fluid dynamics solver based on Reynolds-averaged Navier–Stokes equations. And it carries out aerodynamic optimization designs with a supersonic transport aircraft configuration. The wing shape is parameterized by defining 60 design variables and the wing twist is by four design variables. Meanwhile, the wing thickness constraints are considered. Afterwards, a single-point optimization design aiming at minimum of the supersonic cruise drag is conducted, and in order to consider the transonic cruise condition, a multipoint aerodynamic optimization design aiming at minimum of a weighted drag for the supersonic cruise drag and transonic cruise drag is performed. The analyses of optimization results illustrate the specific drag reduction, the characteristics of pressure distributions for both the supersonic cruise condition and transonic cruise condition, and how the shock wave region and strength have improved on the supersonic cruise condition. The optimization design this paper presents realizing the drag reduction is quite practical and effective, which is instructive in supersonic aircraft design.

Aerodynamic optimization for variable-speed wind turbines based on wind energy capture efficiency

The variable-speed wind turbine (VSWT) is a dominant type of wind power generator. In order to improve wind energy production, its off-design performance has been considered for aerodynamic optimization, since it frequently operates at non-optimal tip speed ratio (TSR) in the maximum power point tracking (MPPT) mode. In this paper, the objective function for multi-point aerodynamic optimization is firstly derived as wind energy capture efficiency. Then, a new multi-point aerodynamic design method whose objective function can approximate wind energy capture efficiency is proposed. Since the proposed optimization aims to increase the closed-loop efficiency with a clear physical meaning, static aerodynamic performance and MPPT dynamics can be better coordinated and correspondingly higher wind energy production of VSWTs can be achieved. Finally, using the 1.5 MW and 5.0 MW VSWTs developed by National Renewable Energy Laboratory (NREL) as the baseline, the proposed method is verified by simulations with commercial software Bladed and experiment test on a wind turbine testbed.

Multi-Level Multi-Objective Multi-Point Optimization System for Axial Flow Compressor 2D Blade Design

This paper introduces a multi-level framework to perform a multi-objective multi-point aerodynamic optimization of the axial compressor blade. This framework results in a considerable speed-up of the design process by reducing both the design parameters and the computational effort. To reduce the computational effort, optimization procedure is working on two levels of sophistication. Fast but approximate prediction methods has been used to find a near-optimum geometry at the firs-level, which is then further verified and refined by a more accurate but expensive Navier–Stokes solver. Surface curvature optimization was carried out in a first-level as a meta-function. Genetic algorithm and gradient-based optimization were used to optimize the parameters of first-level and second-level, respectively. This procedure considers both the aerodynamic and mechanical constraints. An initial blade has been optimized with three different design targets to highlight the ability of the design method and to develop design know-how. Leading-edge shape and curvature distributions of pressure and suction surface had major effects on the design philosophies of the blades. The result shows about −22.5 % reductions in pressure-loss coefficient at design condition and 23.6 % improvement in the allowable incidence-angle range at off-design conditions compared to the initial blade.

Multi-point aerodynamic optimization of the rotor blade sections of an axial-flow impulse air turbine for wave energy conversion

The oscillating water column (OWC) equipped with an air turbine is one of the most actively studied devices for wave energy conversion. It consists of a partially submerged hollow structure whose upper part forms an air chamber and whose immersed part is open to the action of the sea waves. The incident waves excite the internal free surface of the entrained water mass whose oscillation produces a reciprocating air flow that drives a turbine installed in a duct between the chamber and the atmosphere. This paper describes a new two-step method for the optimization of two-dimensional blade sections of an axial-flow impulse air turbine for OWC wave energy converters. Firstly, an inverse design method imposes an almost constant pressure-load along the axial chord by changing the camber line slope. Secondly, a thickness distribution optimization flattens the pressure distribution and decreases the suction peaks at the leading and trailing edges. An optimized geometry of an axial-flow self-rectifying impulse turbine rotor is presented to show the capabilities of the proposed methodology. The three-dimensional blade geometry is generated by stacking optimized sections along the spanwise direction. The rotor efficiency is computed through a three-dimensional CFD (Computational Fluid Dynamics) simulation for several flow rate conditions.

2419 データマイニングを活用した次世代旅客機の主翼設計(OS7-4 設計と最適化IV-空力特性・積層構造-,OS7 設計と最適化)

Multi-point aerodynamic optimization of a transonic wing using data mining is discussed. Design problem has two objectives which are minimization of drag coefficient at Mach number 0.6 and 0.8 respectively. Here, Mach number 0.6 is considered as a subsonic condition, and Mach number 0.8 is considered as a transonic condition with the local shock. To reduce the local shock that causes wave drag, the sweep back angle is required in transonic condition. On the other hand, the sweep back angle reduces lift to drag ratio in subsonic condition. Thus, a complex high lift device like a flap is required. Moreover, the torsion at wing root becomes stronger with high sweep back angle. As a result, the wing structure weight becomes heavy. To design high efficient new generation civil aircraft, the design knowledge which implements a subsonic and a transonic aerodynamic performance simultaneously with few structure penalty is expected. In this study, tapered wing geometry is defined with two cross sections. 31 sample designs are calculated by the unstructured Euler solver and Kriging surrogate models for the resulting drag coefficient of subsonic and transonic condition are constructed. Using these models, non-dominated solutions are obtained by genetic algorithm (GA). Analysis of variance (ANOVA) and Self-organized map (SOM), which are data mining techniques, are also applied to obtain the relationship between design space and solution space. According to this result, there is trade-off between two objective functions and compromised design can be considered. According to data mining result, there is possible to find the design which achieve low drag with low sweep back angle and contrived cross sections.