ng H. You

Loose Fluid-Structure Coupled Approach for a Rotor in Descent Incorporating Fuselage Effects

A loose coupling approach is used to combine a comprehensive structural dynamics code CAMRAD II and a computational fluid dynamics solver KFLOW to validate the data and to identify the effect of fuselage on the aeroelastic behavior of the second higher harmonic rotor acoustic test rotor. The computations are made using isolated rotor and rotor–fuselage models. To demonstrate the effect of a fuselage, the shaft tilt angles remain identical for both configurations. A good correlation has been obtained with the present computational fluid dynamics/comprehensive structural dynamics method. It is observed that a rotor–fuselage model improves the correlation significantly in terms of magnitudes and phases of the airloads solution. All the blade–vortex interaction peaks are captured accurately, and the phase shift in the section normal forces improves significantly, with the inclusion of a fuselage. The sources of improvements are investigated, considering the vorticity distributions and induced velocity fields ...

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

Validation of comprehensive dynamics analysis predictions for a rotor in descending flight

Purpose – The purpose of this paper is to evaluate the prediction capability of comprehensive structural dynamics (CSD) analysis codes for the higher harmonic control aeroacoustic rotor test (HART) II data.Design/methodology/approach – A nonlinear flexible multibody dynamics analysis code DYMORE, as well as the comprehensive analytical model of rotorcraft aerodynamics and dynamics (CAMRAD) II, are used to perform the task. The predicted results on rotating free vibration analysis, airloads, blade elastic motions, and structural moments are correlated with the measured data for the baseline, minimum noise, and minimum vibration cases.Findings – The DYMORE analysis results with a free wake model show a good performance in capturing blade vortex interaction peaks in the prediction of section normal forces but apparently with a phase shift problem. The high‐frequency behavior in the airloads signal does not affect much on the aeroelastic response and structural moments of the rotor.Originality/value – The pre...

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.