The generation of reduced-order models (ROM) for the evaluation of unsteady and nonlinear aerodynamic loads are investigated. The ROM considered is an indicial theory based on the convolution of step functions with the derivative of the input signal. The step functions are directly calculated using the results of RANS simulations and a grid movement tool. Results are reported for a two dimensional airfoil and a UCAV configuration. Wind tunnel data are first used to validate the prediction of static and unsteady coefficients at both low and high angles of attack, with good agreement obtained for all cases. The generation of the aerodynamic models is described. The focus of the paper shifts to assess the validity of studied ROMs with respect to new maneuvres. This is accomplished by comparison of the model output with time-accurate CFD simulations. The results show that the ROMs can accurately model the unsteady loads in response to slow and fast pitch and plunge motions.

Computational Investigation into the Use of Response Functions for Aerodynamic-Load Modeling

Multi-objective reliability-based design optimization approach of complex structure with multi-failure modes

Indicial functions and flutter derivatives: A generalized approach to the motion-related wind loads

/pdf/a-state-of-the-art-review-on-uncertainty-analysis-of-rotor-rffe038u.pdf

A state-of-the-art review on uncertainty analysis of rotor systems

This paper presents a multidisciplinary optimization procedure for enhancing the aerodynamic and aeroacoustic performance of a forward-curved blade centrifugal fan for residential ventilation. Flow...

Aerodynamic and aeroacoustic optimization for design of a forward-curved blades centrifugal fan:

Reliability-based design optimization (RBDO) of the NASA stage 37 axial compressor is performed using an uncertainty model for stall margin in order to guarantee stable operation of the compressor. The main characteristics of RBDO for the axial compressor are summarized as follows: First, the values of mass flow rate and pressure ratio in stall margin calculation are defined as statistical models with normal distribution for consideration of the uncertainty in stall margin. Second, Monte Carlo Simulation is used in the RBDO process to calculate failure probability of stall margin accurately. Third, an approximation model that is constructed by an artificial neural network is adopted to reduce the time cost of RBDO. The present method is applied to the NASA stage 37 compressor to improve the reliability of stall margin with both maximized efficiency and minimized weight. The RBDO result is compared with the deterministic optimization (DO) result which does not include an uncertainty model. In the DO case, stall margin is slightly higher than the reference value of the required constraint, but the probability of stall is 43%. This is unacceptable risk for an aircraft engine, which requires absolutely stable operation in flight. However, stall margin obtained in RBDO is 2.7% higher than the reference value, and the probability of success increases to 95% with the improved efficiency and weight. Therefore, RBDO of the axial compressor for aircraft engine can be a reliable design optimization method through consideration of unexpected disturbance of the flow conditions.

/pdf/reliability-based-design-optimization-of-axial-compressor-wuzw5g01go.pdf

Reliability-based design optimization of axial compressor using uncertainty model for stall margin

An unsteady Euler solver is modified to investigate the directionality of nonlinear indicial response to a step change in the angle of attack. An impulsive change in the angle of attack is incorporated by using the field velocity approach, which is known to decouple the step change in the angle of attack from a pitch rate. Numerical results are thoroughly compared against analytical results for two-dimensional indicial responses. The same method is applied to investigate the directionality of nonlinear indicial responses. It is found that directionality is mainly due to the asymmetry of initial shock locations. Since the directionality of the pitching moment responses is significant in the critical Mach number region, it is also shown that consideration of the directionality is crucial for accurate modeling of the nonlinear indicial functions.

Numerical Investigation on the Directionality of Nonlinear Indicial Responses

The demands for small, high performance and high loaded aircraft compressor are increased in the world. But the design requirements become increasingly complex to design these high technical engines, the requirement of the design optimization become increased. The optimal design result of several disciplines show different tendencies and nonlinear characteristics of the compressor design, the multidisciplinary design optimization method must be considered in compressor design. Therefore, the artificial Neural Net method is adapted to make the approximation model of 3-stage axial compressor design optimization for considering the nonlinear characteristic. At last, the optimal result of this study is compared to that of previous study.

Sangwon Hong

Papers

Reliability-based design optimization of axial compressor using uncertainty model for stall margin

Numerical Investigation on the Directionality of Nonlinear Indicial Responses

Multidisciplinary Design Optimization of 3-Stage Axial Compressorusing Artificial Neural Net