Sung N. Jung

Validation of HART II Structural Dynamics Predictions Based on Prescribed Airloads

In this study, the accuracy of CSD (Comprehensive Structural Dynamics) analysis on the evaluation of blade aeroelastic responses and structural loads of HART(Higher harmonic Aeroacoustic Rotor Test) II baseline rotor is assessed using a comprehensive rotorcraft dynamics code, CAMRAD II, and a nonlinear flexible multi-body dynamics analysis code, DYMORE. Considering insufficient measurement data for HART II rotor, prescribed airloads computed by a three-dimensional compressible flow solver KFLOW are used to replace the lifting-line airloads and thereby enhance the prediction capability of the comprehensive analyses. The CSD results on blade elastic deflections using the prescribed airloads indicate more oscillatory behavior than those by lifting-line based approaches, but the wave pattern becomes improved by including artificial damping into the rotor system. It is demonstrated that the structural load predictions are improved significantly by the prescribed airloads approach against the measured data, as compared with an isolated CSD analysis

Modern Computational Fluid Dynamics/Structural Dynamics Simulation for a Helicopter in Descent

In this work, several computational-fluid-dynamics-based approaches are employed to validate the airloads, trim angles, blade elastic motions, vortex positions, and structural loads of a rotor in low-speed, descending flight. To this end, two different comprehensive codes, CAMRAD II and DYMORE, are coupled with a computational fluid dynamics code, KFLOW, using a loose coupling methodology. A computational fluid dynamics approach using the measured blade motions is also carried out for the validation. For both clarity and consistency required in the relative comparison between different methods, an identical computational fluid dynamics grid system is used for the study. A fuselage effect is considered in the analysis. The predicted results are correlated against the measured data. CAMRAD II coupling shows good prediction for low-frequency loadings, elastic motions, and structural lag bending and torsion moments. DYMORE coupling demonstrates good matches on trim control angles, blade vortex interaction air...

Data Transfer Schemes in Rotorcraft Fluid-Structure Interaction Predictions

For a CFD (computation fluid dynamics)/CSD (computational structural dynamics) coupling, appropriate data exchange strategy is required for the successful operation of the coupling computation, due to fundamental differences between CFD and CSD analyses. This study aims at evaluating various data transfer schemes of a loose CFD/CSD coupling algorithm to validate the higher harmonic control aeroacoustic rotor test (HART) data in descending flight. Three different data transfer methods in relation to the time domain airloads are considered. The first (method 1) uses random data selection matched with the timewise resolution of the CSD analysis whereas the last (method 2) adopts a harmonic filter to the original signals in CFD and CSD analyses. The second (method 3) is a mixture of the two methods. All methods lead to convergent solutions after a few cycles of coupling iterations are marched. The final converged solutions for each of the data transfer methods are correlated with the measured HART data. It is found that both method 1 and method 2 exhibit nearly identical results on airloads and blade motions leading to excellent correlations with the measured data while the agreement is less satisfactory with method 3. The reason of the discrepancy is identified and discussed illustrating CFD-/CSD-coupled aeromechanics predictions.