The inherent aeromechanical complexity of a rotor system necessitated the comprehensive analysis code for helicopter rotor system. In the present study, an aerodynamic analysis module has been developed as a part of rotorcraft comprehensive program. Aerodynamic analysis module is largely classified into airload calculation routine and inflow analysis routine. For airload calculation, quasi-steady analysis model is employed based on the blade element method with the correction of unsteady aerodynamic effects. In order to take unsteady effects -body motion effects and dynamic stall -into account, aerodynamic coefficients are corrected by considering Leishman-Beddoes's unsteady model. Various inflow models and vortex wake models are implemented in the aerodynamic module to consider wake induced inflow. Specifically, linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's induced inflow distribution and sectional normal force coefficients of AH-1G. In order to validate unsteady aerodynamic model, 2-D unsteady model for NACA0012 airfoil is validated against aerodynamic coefficients of McAlister's experimental data.
Methanol is metabolized in the body to highly toxic formaldehyde and formate when consumed accidentally. Methanol has been typically analyzed with gas chromatography-flame ionization detector (GC-FID). However, its retention time may overlap with other volatile compounds and lead to confusion. Alternative analysis of methanol using gas chromatography/mass spectrometry (GC/MS) also has limitations due to its similar molecular weight with oxygen and low boiling point. In this study, methanol and internal standard of deuterium-substituted ethanol were derivatized with 3,4-dihydro-2H-pyran under acid catalysis using concentrated hydrochloric acid. The reaction products including 2-methoxytetrahydropyran were extracted with solid-phase microextraction followed by GC/MS analysis. This method was successfully applied to measure the lethal concentration of methanol in the blood of a victim with a standard addition method to overcome the complex matrix effect of the biospecimen. Identification of the metabolite formate by ion chromatography confirmed the death cause to be methanol poisoning. This new method was a much more convenient and reliable process to measure methanol in complex matrix samples by reducing sample pretreatment effort and cost.
In this study, the aeroelastic analysis of rotorcraft in forward flight has been performed using dynamic wake model to handle unsteady aerodynamics. The quasi-steady airload model based on the blade element method has been coupled with dynamic wake model developed by Peters and He. The nonlinear steady response to periodic motion is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim for stability analysis. The aerodynamic and structural characteristics of dynamic wake model are validated against other numerical analysis results by comparing induced inflow and blade tip deflections(flap, lag). In addition, mechanism of aeroelastic instability will be investigated by evaluating the aeroelastic stability using different linear inflow and dynamic wake models at a low advance ratio. As the influences of nonlinearity result in significant differences in the blade deflection behavior and aeroelastic characteristics, an appropriate analysis is required to capture these attributes. The dynamic wake model is more accurate than the linear inflow model is at low advance ratios (0.0 ≤ µ ≤ 0.15) yet more time-effective than 3-D aerodynamic models. Thus it is most suitable for aeroelastic analysis in the preliminary design of a helicopter.
NomenclatureC T = thrust coefficient e = strain at the datum line m = harmonic function number n = shape function number r = nondimensional blade radial coordinate, r =r/R t = nondimensional time, t =Ωt w = warping deformation α s = longitudinal shaft tilt angle, degree α n m , β n m = induced inflow expansion coefficients δT = variation of the strain energy 2 δU = variation of the kinetic energy δW = variation of the virtual work θ 0= collective pitch angle, degree θ 1c = lateral cyclic pitch angle, degree θ 1s = longitudinal cyclic pitch angle, degree κ i = difference in curvature before and after deformation λ 0 = mean induced inflow ratio λ = induced inflow ratio µ = advance ratio ϕ s = lateral shaft tilt angle, degree ϕ j r = radial expansion function ψ = azimuth, angle, rad ( )' = differentiation in the axial direction ( ), i = differentiation in 2 and 3 directions at a cross-section
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