# Browsing by Subject "Rotor"

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Item Measurement of deformation of rotating blades using digital image correlation(2011-08) Lawson, Michael Skylar; Sirohi, Jayant; Ravi-Chandar, KrishnaswamyShow more An experimental study on the application of Digital Image Correlation (DIC) to measure the deformation and strain of rotating blades is described. Commercial DIC software was used to obtain measurements on three different types of rotors with diameter ranging from 18 to 39 and with varying flexibility to explore applicability of the technique over a breadth of scales. The image acquisition was synchronized with the frequency of rotation such that images could be obtained at the same phase and the consistency of measurements was observed. Bending and twist distributions were extracted from the data with deformation as high as 0.4 measured with a theoretical accuracy of 0.0038 and span-wise resolution of 0.066. The technique was demonstrated to have many advantages including full-field high resolution results, non-intrusive measurement, and good accuracy over a range of scales. The span-wise deformation profiles from the DIC technique are used in conjunction with Blade Element Momentum Theory to calculate the thrust and power consumed by the rotor with rigid vi blades; results are comparable to load cell measurements albeit thrust is somewhat under-predicted and power is over-predicted. Overall, the correlation between DIC calculated thrust and BEMT approximations for comparable blades with constant pitch were within 12% through the onset of stall. Measurement of flexible blade deformation that would not have been possible with other techniques demonstrated the utility of the DIC method and helped to confirm predictions of flexible blade behavior.Show more Item Stability and turbulence characteristics of a spiraling vortex filament using proper orthogonal decomposition(2015-05) Mula, Swathi Mahalaxmi; Tinney, Charles Edmund, 1975-Show more The stability and turbulence characteristics of a vortex filament emanating from a single-bladed rotor in hover are investigated using proper orthogonal decomposition. The rotor is operated at a tip chord Reynolds number and a tip Mach number of 218,000 and 0.22, respectively, and with a blade loading of CT /σ = 0.066. In-plane components of the velocity field (normal to the axis of the vortex filament) are captured by way of 2D particle image velocimetry with corrections for vortex wander being performed using the Γ1 method. Using the classical form of POD, the first POD mode alone is found to encompass nearly 75% of the energy for all vortex ages studied and is determined using a grid of sufficient resolution as to avoid numerical integration errors in the decomposition. The findings reveal an equal balance between the axisymmetric and helical modes during vortex roll-up which immediately transitions to helical mode dominance at all other vortex ages. This helical mode is one of the modes of the elliptic instability. While the snapshot POD is shown to reveal similar features of the first few energetic modes, the classical POD is employed here owing to the easier interpretation of the Fourier-azimuthal modes. The spatial eigenfunctions of the first few Fourier-azimuthal modes associated with the most energetic POD mode are shown to be sensitive to the choice of the wander correction technique used. Higher Fourier-azimuthal modes are observed in the outer portions of the vortex and appeared not to be affected by the choice of the wander correction technique used.Show more Item Study of compressible flow through a rotating duct(2015-08) Karpatne, Anand; Sirohi, Jayant; Goldstein, David B; Raja, Laxminarayan L; Tinney, Charles E; Shannon, Daniel WShow more Several rotorcraft applications such as circulation control and tip jet driven rotors involve internal spanwise flow along the interior of a rotor blade. This dissertation describes a quasi 1-D numerical model of unsteady flow through a duct rotating about one end along with experimental validations. The numerical model is suitable for inclusion in the conceptual design stage for helicopter rotor blades with internal spanwise flow. To this end, centrifugal as well as coriolis effects, frictional losses, duct sweep and time-dependent duct boundary conditions are modeled, and a spanwise flow control valve can be included. One dimensional Euler equations are solved inside the duct using a finite volume formulation in which the advective fluxes are approximated using the Advective Upwind Splitting Method (AUSM). The model is used to explore the behavior of flow inside a 2 m long duct with a circular crosssection, rotating at tip speeds of up to 260 m/s. In the inviscid limit, at a rotor tip speed of 213 m/s, the model predicted the evolution of a shock which showed periodic oscillations with a time period of approximately 17.5 rotor revolutions. However, when friction was included, a shock did not form until the rotor tip speed was ~ 260 m/s. The effects of suddenly opening a flow control valve at different spanwise stations, x [subscript valve] = 0.0R, x [subscript valve] = 0.5R and x [subscript valve] = R, were also studied numerically. Predictions of both steady and transient flow properties from this model are validated with experiments conducted on a 1.32 m long cylindrical duct, with a cross-sectional diameter of 52 mm, rotating at speeds of upto 1050 RPM (Tip Speed = 145 m/s). Spanwise pressure distribution, duct velocity, temperature, hub forces and moments results from the numerical model showed good correlation with experiments. Considerable internal mass flow rate (~ 0.3 kg/s) was also observed. In the presence of a time-varying valve at the inlet, transient spanwise pressure variations showed periodic fluctuations in pressure which diminished once the valve was fully open. The quasi 1-D model was found to be a much faster computational tool than any conventional 3-D CFD solver to study spanwise flow inside rotor blades. The experiments revealed key information about pressure at the duct's outlet. It was observed that when the duct's inlet is closed, the duct's outlet pressure is less than its ambient value. The knowledge of these boundary conditions is essential in modeling flow through rotating ducts. For more accuracy, the current internal flow solver could be coupled with an external flow code to iteratively obtain boundary conditions at their interface.Show more