Unsteady Adjoint Approach for Design Optimization of Flapping Airfoils

Lee, Byung Joon; Liou, Meng-Sing

doi:10.2514/1.j051663

Cited by 13 publications

(6 citation statements)

References 25 publications

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“…A much more efficient way to calculate the gradient information is using the adjoint method presented in [18][19][20], thus providing the full gradient at a cost of solving a linear system. Although the adjoint technique can be robust and stable for realistic flow characteristics, such as flow separations [21], challenges related to its industrial applicability are not sufficiently resolved yet. Research towards that direction is currently being conducted within the EC ITN IODA project [22].…”

Section: Numerical Setup and Cfd Simulationmentioning

confidence: 99%

Numerical and Experimental Investigations on Optimized 3D Compressor Airfoils

Mihalyovics

Brück

Peitsch

et al. 2018

Volume 2A: Turbomachinery

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The objective of the presented work is to perform numerical and experimental studies on compressor stators. This paper presents the modification of a baseline stator design using numerical optimization resulting in a new 3D stator. The Rolls Royce in-house compressible flow solver HYDRA was employed to predict the 3D flow, solving the steady RANS equations with the Spalart-Allmaras turbulence model, and its corresponding discrete adjoint solver. The performance gradients with respect to the input design parameters were used to optimize the stator blade with respect to the total pressure loss over a prescribed incidence range, while additionally minimizing the flow deviation from the axial direction at the stator exit. Non-uniform profile boundary conditions, being derived from the experimental measurements, have been defined at the inlet of the CFD domain. The presented results show a remarkable decrease in the axial exit flow angle deviation and a minor decrease in the total pressure loss. Experiments were conducted on two compressor blade sets investigating the three-dimensional flow in an annular compressor stator cascade. Comparing the baseline flow of the 42° turning stator shows that the optimized stator design minimizes the secondary flow phenomena. The experimental investigation discusses the impact of steady flow conditions on each stator design while focusing on the comparison of the 3D optimized design to the baseline case. The flow conditions were investigated using five-hole probe pressure measurements in the wake of the blades. Furthermore, oil-flow visualization was applied to characterize flow phenomena. These experimental results are compared with the CFD calculations.

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Section: Numerical Setup and Cfd Simulationmentioning

confidence: 99%

Numerical and Experimental Investigations on Optimized 3D Compressor Airfoils

Mihalyovics

Brück

Peitsch

et al. 2018

Volume 2A: Turbomachinery

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“…For = 0, the flow is steady, and for 0 ≤ ≤ 0.05, the flow can be considered quasi-steady; that is, unsteady effects are generally small. Flows with characteristic reduced frequencies above 0.05 are considered unsteady [5,6]. For a helicopter rotor in forward flight (Figure 3), the local sectional velocity, which appears in the denominator of the reduced frequency expression, is constantly changing.…”

Section: Helicopter Rotor Blade Aerodynamicsmentioning

confidence: 99%

“…The problem of finding the airloads on an oscillating airfoil was solved by Theodorsen, who gave a solution to the unsteady airloads on a 2D harmonically oscillated airfoil in inviscid, incompressible flow, with the assumption of small disturbances [6]. Both the airfoil and its shed wake were represented by a vortex sheet with the shed wake extending as a planar surface from the trailing edge downstream to infinity.…”

Section: The Airloads On An Oscillating Airfoilmentioning

confidence: 99%

Nonlinear Characteristics of Helicopter Rotor Blade Airfoils: An Analytical Evaluation

Rotaru

2013

Mathematical Problems in Engineering

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Some results are presented about the study of airloads of the helicopter rotor blades, the aerodynamic characteristics of airfoil sections, the physical features, and the techniques for modeling the unsteady effects found on airfoil operating under nominally attached flow conditions away from stall. The unsteady problem was approached on the basis of Theodorsen's theory, where the aerodynamic response (lift and pitching moment) is considered as a sum of noncirculatory and circulatory parts. The noncirculatory or apparent mass accounts for the pressure forces required to accelerate the fluid in the vicinity of the airfoil. The apparent mass contributions to the forces and pitching moments, which are proportional to the instantaneous motion, are included as part of the quasi-steady result.

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“…Furthermore, the flow pattern at each primal time step has to be stored, as it is needed in the adjoint calculation. This method has been formulated for flow computations in frequency [7] and temporal space [8], but the high demand in terms of memory and compute power are only acceptable in applications where it is essential to resolve unsteadiness, such as in the optimisation of flapping air foils [9].…”

Section: Introductionmentioning

confidence: 99%