11,958 research outputs found
Prediction of Helicopter Rotor Hover Performance using High Fidelity CFD Methods
No abstract available
Numerical Simulations on the PSP Rotor Using HMB3
This work presents CFD analyses of the isolated Pressure Sensitive Paint (PSP) model rotor blade
in hover and forward flight using the structured multi-block CFD solver of Glasgow University. In
hover, two blade-tip Mach numbers (0.585 and 0.65) were simulated for a range of blade pitch angles
using fully-turbulent flow and the k-ω SST model. Results at blade-tip Mach number of 0.585 showed
a fair agreement with experimental Figure of Merit and surface pressure coefficients obtained in the
Rotor Test Cell (RTC) at NASA Langley Research Center. Comparisons are presented at blade-tip
Mach number of 0.65 in terms of integral blade loads, surface pressure coefficients and position of
the tip-vortex cores with published numerical data. Finally, the flow around the PSP rotor in forward
flight was also computed at medium thrust (CT =0.006) and results were compared with published
experimental data
Towards High-order Methods for Rotorcraft Applications
This work presents CFD results obtained with an efficient, high-order, finite-volume scheme. The formulation is
based on the variable extrapolation MUSCL-scheme, and high-order spatial accuracy is achieved using correction
terms obtained through successive differentiation. The scheme is modified to cope with physical and multiblock
mesh interfaces, so stability, conservativeness, and high-order accuracy are guaranteed. Results with the proposed
scheme for steady flows, showed better wake and higher resolution of vortical structures compared with
the standard MUSCL, even when coarser meshes were employed. The method was also demonstrated for unsteady
flows using overset and moving grids for the UH-60A rotor in forward flight and the ERICA tiltrotor in aeroplane
mode. The present method adds CPU and memory overheads of 47% and 23%, respectively, in performing
multi-dimensional problems for routine computations
Air pollution and unleaded gasoline in Mexico City
Using a spline regression model and a monthly time series from January 1989 to December 2004 for Mexico City, we test for changes in the time trend for air pollution that coincide with the introduction of a new and relatively expensive unleaded gasoline in September 1990. At this time, new cars were required to have catalytic converters and leaded gasoline was significantly cheaper than unleaded gasoline. The price difference provided an incentive to use leaded gasoline in automobiles that were not suited to its use, thereby increasing emissions. We find that there was a statistically significant and adverse change in the pollution time trend after September 1990 that persisted until leaded gasoline was eliminated from the Mexico City market eight years later. The use of leaded gasoline in new cars is a possible explanation for this result.
Tiltrotor CFD part I: validation
This paper presents performance analyses of the model-scale ERICA and TILTAERO tiltrotors and of the full-scale XV-15 rotor with high-fidelity computational fluids dynamics. For the ERICA tiltrotor, the overall effect of the blades on the fuselage was well captured, as demonstrated by analysing surface pressure measurements. However, there was no available experimental data for the blade aerodynamic loads. A comparison of computed rotor loads with experiments was instead possible for the XV-15 rotor, where CFD results predicted the FoM within 1.05%. The method was also able to capture the differences in performance between hover and propeller modes. Good agreement was also found for the TILTAERO loads. The overall agreement with the experimental data and theory for the considered cases demonstrates the capability of the present CFD method to accurately predict tiltrotor flows. In a second part of this work, the validated method is used for blade shape optimisation
Accurate Predictions of Hovering Rotor Flows Using CFD
With work on the S-76 rotor providing encouraging results regarding the prediction of integral
loads with CFD in hover, the XV-15 rotor is now analysed. Fully turbulent and transitional results
are obtained showing the capability of modern CFD methods. The transition onset and distribution of
skin friction are well predicted and were found to have a mild effect on the overall figure of merit. This
work also shows the potential of transport-based models for transition prediction in complex 3D flows.
Finally, hover simulations for the PSP blade are also shown in terms of surface pressure coefficient and
wake visualisation
Determinants of Meats Purchase Behavior by Ethnic Groups
Farmers and food companies need to assess their production and marketing strategies for nurturing business opportunities that will arise from the simultaneous increase in population and income of Hispanics in the United States. Previous studies on demand for meat products have not received much attention on the determinants of meats purchase behavior by Hispanics in relation to other ethnic groups. This study investigates the impact of ethnicity and the determinants of meats purchase behavior in the U.S. by using single Probit equations. The analyzed data comes from the U.S. Consumer Expenditure Survey. The results indicate that ethnicity plays an important role in the purchase behavior of meat products, as well as household size and income.consumer behavior, marketing, food demand, Hispanic food, hispanic food market, Latin foods, comida latina, alimentos, ethnic foods, Agribusiness, Consumer/Household Economics, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety, Industrial Organization, Marketing, D01, D03, D12, L14, L66, M31, M37,
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