Code-to-code comparison study on rotor aeromechanics in descending flight

Abstract

This paper conducts the aeromechanics study using the two different rotorcraft computational structural dynamics (CSD) codes, CAMRAD II and DYMORE II, for the rotor in low-speed descending flight. The three test cases of the HART (Higher-harmonic control Aeroacoustic Rotor Test) I -baseline, minimum noise, and minimum vibration- are considered for the present study of the blade-vortex interaction (BVI) airloads, rotor trim, blade elastic deformations, and blade structural loads. The two prediction results are compared to each other for code-to-code comparison study as well as the measured data. Although CAMRAD II and DYMORE II use different theories and models, most predictions results are quite similar to each other and compared fairly well with the wind tunnel test data. For all the three test cases, the two rotorcraft CSD analyses show good prediction on the fluctuations of the section normal force (M2Cn) due to BVI, but both over-predict the trimmed collective pitch angle. The blade elastic deformations such as flap deflection and elastic torsion deformation at the tip are reasonably predicted by both rotorcraft CSD analyses. CARMAD II and DYMORE II both correlate reasonably the blade structural loads such as flap bending, lead-lag bending, and torsion moments with the measured data; however CAMRAD II results using the multiple-trailer wake model are slightly better than DYMORE II predictions with the single wake panel model.