Deg Yaw Research Articles

Impact of Disc Wheel Geometry on Aerodynamic Performance: A Computational Fluid Dynamics Investigation

AbstractAerodynamic drag is the main resistive force in cycling at high speeds and on flat terrain, so reducing it is critical to improving cyclist performance. Aerodynamic comparisons have been made in the past between different types of wheels, and disk wheels were often the best performers. However, to the best of our knowledge, there are no studies in the available literature on how modifications to the disk wheel geometry can improve its performance. Therefore, this paper studies and compares the aerodynamics of disk wheels with flat side disks and with curved side disks (lenticular). Moreover, semilenticular front wheels with an asymmetrical shape are introduced. All but one of the simulated (semi-)lenticular wheels perform better than the flat disk wheels at all yaw angles, e.g., the maximum CD reduction was 5.5%, 10.9%, and 87.5% at 0 deg, 4 deg, and 8 deg yaw angle, respectively. Semilenticular wheels provide a lower CD at medium and large yaw angles compared to corresponding symmetric lenticular wheels. Moreover, the large influence of the ratio of tire width to wheel width on the aerodynamic drag of cycling wheels is confirmed. These results will help riders in their wheel choice and will help manufacturers to design future disk wheels.

Differential effects of vision upon the accuracy and precision of vestibular-evoked balance responses.

Key points Effective balance control requires the transformation of vestibular signals from head‐ to foot‐centred coordinates in order to move the body in an appropriate direction.This transformation process has previously been studied by analysing the directional accuracy of the averaged sway response to multiple electrical vestibular stimuli (EVS).Here we studied trial‐by‐trial variability of EVS responses to measure any changes in directional precision which may be masked by the averaging process.We found that vision increased directional variability without influencing the mean sway direction, demonstrating that response accuracy and precision are dissociable.These results emphasise the importance of single trial analysis in determining the efficacy of vestibular control of balance. Vestibular information must be transformed from head‐ to‐foot‐centred coordinates for balance control. This transformation process has previously been investigated using electrical vestibular stimulation (EVS), which evokes a sway response fixed in head coordinates. The craniocentric nature of the response has been demonstrated by analysing average responses to multiple stimuli. This approach misses any trial‐by‐trial variability which would reflect poor balance control. Here we performed single‐trial analysis to measure this directional variability (precision), and compared this to mean performance (accuracy). We determined the effect of vision upon both parameters. Standing volunteers adopted various head orientations (0, ±30 and ±60 deg yaw) while EVS‐evoked response direction was determined from ground reaction force vectors. As previously reported, mean force direction was orientated towards the anodal ear, and rotated in line with head yaw. Although vision caused a ∼50% reduction in response magnitude, it had no influence on the direction of the mean sway response, indicating that accuracy was unaffected. However, individual trial analysis revealed up to 30% increases in directional variability with the eyes open. This increase was inversely correlated with the size of the force response. The paradoxical observation that vision reduces the precision of the balance response may be explained by a multi‐sensory integration process. As additional veridical sensory information becomes available, this lessens the relative contribution of vestibular input, causing a simultaneous reduction in both the magnitude and the precision of the response to EVS. Our novel approach demonstrates the importance of single‐trial analysis in revealing the efficacy of vestibular reflexes.

Steady-State Hydrodynamic Power Attenuation by Finned-Buoys

Results of experimental and computational fluid dynamics (CFD) studies conducted to compare the flow-energy-attenuating performances of two different buoy configurations are presented. A finned-body was experimentally studied in two orientations—one with a splitter and one in a 22.5 deg yaw orientation (with no splitter). The finned-buoy is designed for both wave and current attenuation; however, only the current application is discussed here. Scaled models were subjected to wind tunnel testing and CFD analyses. For this study, the steady-state drag coefficient (CD) is considered to be the performance measure. The CFD model is used to match the physical testing by utilizing the k–ω turbulence model. Reynolds numbers (based on the tip-to-tip fin diameter) approaching the drag crisis are used to evaluate the bodies of interest, both of which have an aspect ratio (draft-to-diameter) of 1.85. The finned-bodies do encounter a drag crisis (as commonly seen with a cylinder), since the fins cause the buoys to act as a bluff body. The flow structures around the bodies are examined and compared to those predicted by established theories. For the finned-body, the 22.5 deg yaw orientation is found to have a consistently higher drag than the splitter orientation. The drag enhancement is explained by two phenomena. The first is a low-pressure area located in pockets adjacent to the upstream fins. The second is the absence of the drag-crisis, due to fixed separation points at the fin tips for all Reynolds numbers.

The Impact of Familiarity on Performance when Seeking a Face in a Crowd

Relatively few studies have examined the time course by which unfamiliar faces accrue familiarity, and those that have rely upon ‘internal feature advantage’ for familiar faces, requiring that central or external facial features are selectively ablated (Young et al 1985, Perception14). In the present study, a procedure was used that required observers to seek a pre-cued face from among a number of alternatives, akin to finding a face in a crowd. Two factors were examined across 450 trials divided into blocks of 50 trials, run in counterbalanced order with 24 observers: viewpoint (the use of front and 30 deg yaw face stimuli at learning and search); and search target familiarity, being either unfamiliar (changed from trial-to-trial), learned (re-used from trial-to-trial), or familiar a priori (famous). In common with several existing studies, we found that the learned face condition yielded significantly decreased search time relative to unfamiliar faces (p<0.05) and eliminated viewpoint effects, a hallmar...

Flush-Wall, Diamond-Shaped Fuel Injector for High Mach Number Scramjets

Experiments on diamond-shaped injectors with sonic injection of heated helium into a nominal Mach 4 airflow are reported. The slender diamond was angled up 60 deg from the wall. These conditions correspond to a Mach 10 scramjet with helium to simulate hydrogen fuel. The diamond was tested at jet-to-freestream momentum flux ratios, q, of 1.04 and 0.49, aligned with the freestream and with 15 deg yaw. For comparison, round injectors angled up 30 deg from the wall with q = 1.75 were also examined. Previous studies have shown that diamond and round injectors each perform best at different values of q. A sampling probe was used for helium concentration with Pilot, cone-static, and total temperature probes for other flow properties. For q = 1.04, the diamonds penetrated about 50% higher than the round injector and produced a 30% wider jet. The diamonds exhibited 10-15 % lower mixing efficiency. The total pressure loss parameter of the aligned diamond was 22% lower, while the yaw angle improved the total pressure loss parameter to 34% lower than the round injector. For the lower q case, the diamond demonstrated 52 % higher penetration and a 39 % wider plume than the round injector, and the mixing efficiency was only 4% lower. The total pressure loss parameter was 32% lower than the round injector. These results confirm earlier, lower Mach number and heavier injectant studies that a slender diamond injector provides significant benefits for penetration and lower total pressure losses.

Improved Harmonic Large-Angle Fuselage Aerodynamics Model

Introduction F LIGHT vehicle simulation, guidance and control law design, and flight performance analysis methods commonly use aerodynamic models based on tabulated force and moment coefficients. Inputs for these models are generally derived from wind-tunnel test data and/or computational fluid dynamics (CFD) results. However, wind-tunnel data are often only available for a limited range of pitch and yaw angles, and CFD computations for a large number of arbitrary attitudes can be expensive. Rotorcraft simulation models require aerodynamic inputs at extreme attitudes and commonly use trigonometric high-angle models to provide smoothly varying data in these regimes.1,2 Other applications for extreme high-angle aerodynamic models are ground-handling simulations, where the wind may come from any azimuth, flight performance analysis at high angles,2 and trajectory analysis of tumbling bodies. This Engineering Note presents a trigonometric, quasi-steady, fuselage aerodynamics model that is valid at all aerodynamic angles with a range of ±180 deg yaw and ±90 deg pitch. This model is based on the C81 high-angle equation (HAE) model found in some rotorcraft simulations1 but with improvements to the usability of the original model. The HAE model uses aerodynamic coefficient inputs at key values of pitch and yaw angles that may come from wind-tunnel tests, CFD analysis, or other sources. A set of sinusoidal functions is used to estimate the values for all six wind-reference fuselage aerodynamic forces and moments at any combination of pitch angle and yaw angle. The HAE model is desirable in that the equations are continuous and easily computed, give the proper trends at all attitudes, include some cross-coupling effects, and require relatively few inputs. The quasi-steady nature of the HAE model makes it unsuitable for situations where time-dependent flow characteristics are significant. This model is not suitable where high accuracy is required and is not expected to capture sudden changes in flow characteristics at critical angles such as the onset of stall or slender forebody vortex shedding. To address this issue, a blending scheme is often used to transition between wind tunnel data (or other high-quality data) at low angles and the HAE model at high angles.1 This Note addresses three limitations with the Ref. 1 model. First, the original model assumes lateral–directional coefficients are con-

Installed F/A-18A inlet flow calculations - A grid study

Full Navier-Stokes calculations on the F/A-18A High Alpha Research Vehicle inlet at 30 deg angle of attack, 0 deg yaw, and a freestream Mach number of 0.2, have been obtained in this study using an algebraic turbulence model with two grids (original and revised). In addition, a limited set of results were obtained using a thinlayer Navier-Stokes (TLNS) code with the revised grid. The limitedness of the results was due to the inadequacy of the grid to meet the requirements of the TLNS code. Results obtained with the original grid were used to determine where further grid refinements and additional geometry were needed. The calculations are compared to a limited amount of available experimental data. The predicted forebody/fuselage surface static pressures compared well with data for all solutions. The predicted trajectory of the vortex generated under the leadingedge extension was different for each solution. These discrepancies are attributed to differences in the grid resolution, turbulence modeling, artificial dissipation, and differencing schemes. All solutions predict that this vortex is ingested by the inlet. The predicted 40-probe rake inlet total pressure recoveries are lower than data and the distortions are higher than data. The results obtained with the revised grid were significantly improved from the original grid results.

Response of an Operational Turbofan Engine to a Simulated Nuclear Blast

This paper describes the results of a measurement program designed to determine the transient response of an air-breathing propulsion system to simulated nuclear blast waves. A Ludwieg-tube facility, incorporating a driver technique consisting of an activating chamber and a nonfrangible diaphragm, was used to create the required shock waves. Detailed measurements were performed at incident shock overpressures of approximately 6.9, 10.3, 13.8, and 17.2 kPa (1.0, 1.5, 2.0, and 2.5 psi). For each of these overpressures, data were obtained for engine speeds of 0, 80, 90, and 100 percent of maximum speed. Typical results are presented for distortion patterns at the fan face for both an extended bellmouth and a S-shaped inlet at either 0 or 20 deg yaw angle.

Contributions of the x-15 program to lifting entry technology

Entries from altitudes greater than 350,000 ft with the X-15 airplane have provided piloting experience and verification of predicted control characteristics and operational techniques. The airplane re-enters as a glider and duplicates several phases in the recovery of higher-performance vehicles, for example, transition from near-zero dynamic pressure to aerodynamic flight, and the terminal-area ranging and landing. During entries, reaction controls have been used to surprisingly high dynamic pressures. Rate command control provided satisfactory control, and hold modes were appreciated by the pilots for secondary control mocjes. With conservatively planned flights, the pilots have had no problem controlling range to base with contact navigation. Landmarks have been observed from above 300,000 ft and 160 miles range. The approach and landing of the low-lift-drag-ratio X-15 airplane has become routine, with relatively small dispersion in touchdown and slideout distance. The speed brakes have been an important control for regulation of ranging for landing; however, the pilots indicated that faster-acting speed brakes would allow more flexible operation. D 9 = L := q = Nomenelatu re drag acceleration due to gravity, ft/sec2 lift dynamic pressure, psf angle of attack, deg pitch angle, deg roll angle, deg yaw angle, deg