C. Tinney

The impact on stability and control of small general aviation aircraft, resulting from ice accumulation on the elevator horn balance, is investigatedusing an experimental data set. The purpose is to determine the linear and non-linear coupling mechanisms between the ice-induced unsteady flow field and the structural response of the elevator horn balance. The linear and quadratic relations between the two

ABSTRACT A higher-order system identification technique will be presented in the context of stochastic estimation, as it is quite useful in the field of (experimental) fluid dynamics. This higher-order spectral stochastic estimation technique was originally developed in the context of Systems Identification. It is shown how this technique defaults to spectral Linear Stochastic Estimation when only the linear kernels are computed. In case of higher-order computations, the system is constructed using a frequency-domain Volterra series and is expressed as a linear algebraic system of equations that are solved for the linear and higher-order transfer kernel coefficients. In the trade-off to seek for higher-order transfer kernels, the increased complexity restricts the analysis to single input/single output. POD based methods can be inserted to alleviate this void whereby time-varying POD coefficients of the output are estimated from POD coefficients of the input. Strengths and weaknesses of the current implementation of this technique will be discussed using simulated data and an application of this method to an axisymmetric jet flow to identify coherent turbulent structures.

The most energetic modes of the turbulent mixing layer from an axisymmetric jet at Mach 0.85 are examined using multi-component forms of the joint POD-Fourier decomposition techniques. Measurements of the velocity field (r, theta cross-plane) are performed using a stereo PIV system traversed along the sound-source regions of the, flow ( zD = 3 to 8, Deltaz = 0.25D). The results indicated a dominance in the m = 5 Fourier-azimuthal mode at z = 3D, with a shift to the m = 3 Fourier-azimuthal mode at z = 8D. A grid sensitivity indicates that the inclusion of additional components in the decomposition are not shown to shift the energy amongst modes, but rather change the relative energy in each mode, thus supporting previous investigations by Citriniti & George [97], Jung et al. [103], and Glauser & George [99] who used the scalar decomposition (streamwise component) in the axisymmetric mixing layer (incompressible) and Ukeiley et al . [58] who used a vector form (streamwise and radial c...

The wandering motion of tip vortices trailed from a hovering helicopter rotor is described. This aperiodicity is known to cause errors in the determination of vortex properties that are crucial inputs for refined aerodynamic analyses of helicopter rotors. Measurements of blade tip vortices up to 260 deg vortex age using stereo particle-image velocimetry (PIV) indicate that this aperiodicity is anisotropic. We describe an analytical model that captures this anisotropic behavior. The analysis approximates the helical wake as a series of vortex rings that are allowed to interact with each other. The vorticity in the rings is a function of the blade loading. Vortex core growth is modeled by accounting for vortex filament strain and by using an empirical model for viscous diffusion. The sensitivity of the analysis to the choice of initial vortex core radius, viscosity parameter, time step, and number of rings shed is explored. Analytical predictions of the orientation of anisotropy corre...

ABSTRACT An experimental investigation of the near pressure field of unbounded subsonic jets has been performed. The near-field pressure was sampled, using linear and azimuthal arrays, on conical surfaces surrounding free jets generated by (1) a single axisymmetric nozzle, (2) a co-axial short-cowl nozzle, and (3) a co-axial short-cowl nozzle with serrations (the co-axial experiments were performed as part of the EU program, CoJeN (AST3-CT-2003-502790), where velocity and temperature-ratios were varied). The objective of the study is to better understand differences in the structure of the flows in terms of their sound production mechanisms. A model representation of the source mechanism associated with coherent-structures in the flow is considered, using both the pressure fluctuations themselves and the pressure-derivative source term from Curie's acoustic analogy. A filtering operation is then applied in order to identify the structure of the radiating source field.