Yaw Effects Research Articles

In-Bore Yaw Effects on Lateral Throw-off and Aerodynamic Jump Behavior for Small Caliber Projectiles Firing Sidewise From Air Vehicles

The present study investigates the effects of in bore-yaw phenomenon on lateral throw-off and aerodynamic jump behavior for small caliber rotational symmetric (both in configuration and mass distribution) projectiles launched horizontally at supersonic firing speeds and various altitudes from high-subsonic air vehicles. The ammunition used is the caliber .50 API M8 bullet type firing from M2 machine automatic gun. The projectile is considered to be eccentrically engraved, tilted as it enters the rifling, and it is assumed that the tilt persists throughout its passage through the rifled barrel of the used weapon system. The modified linear 6-DOF flight simulation modeling is applied for the bullet free-flight trajectory predictions. The coupled epicyclic pitching and yawing motion analysis for the first 100 m of the examined trajectories are taken into account.

Critical conditions of galloping for inclined square cylinders

This paper concerns the study of galloping critical conditions on square cylinders with an arbitrary attitude in the wind flow. It is based on a consistent theoretical model of wind actions, which permits the analysis of a generic-shaped cross-section. A generalized definition of the aerodynamic damping matrix as function of both the angle of incidence and the angle of skew is proposed. The availability of specific experimental data allows a sound definition of aerodynamic actions. The analysis of critical conditions can be performed in closed form in the plane of the aerodynamic damping matrix invariants. Preliminary results obtained in smooth-flow conditions point out that yaw effects might influence critical conditions from a quantitative point of view, but do not destroy the instability domain obtained in the classical cross-flow conditions.

The Bandwidth of Transient Yaw Effects on Vehicle Aerodynamics

A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, the unsteady wakes from other vehicles and as a result of traversing through the stationary wakes of road side obstacles. There is increasing concern about potential differences in aerodynamic behaviour measured in steady flow wind tunnel conditions and that which occurs for vehicles on the road. It is possible to introduce turbulence into the wind tunnel environment (e.g. by developing active turbulence generators) but on-road turbulence is wide ranging in terms of both its intensity and frequency and it would be beneficial to better understand what aspects of the turbulence are of greatest importance to the aerodynamic performance of vehicles. There has been significant recent work on the characterisation of turbulent airflow relevant to road vehicles. The simulation of this time-varying airflow is now becoming possible in wind tunnels and in CFD. Less is known about the range of turbulence length scales and intensities that are significant to the performance of vehicles. It is only necessary to simulate (experimentally or computationally) the Venn intersection of the range of conditions experienced and the range that are important to the vehicle's performance. The focus of this work is on transient yaw fluctuations. Time-resolved simulations of simple two dimensional parametric geometries subjected to yaw transients at a range of different time scales were conducted using Exa Powerflow. The effects of model geometry, Reynolds number yaw fluctuation amplitude and superposition were investigated. It was found that, in general, the flow could be treated as quasi-steady for reduced frequencies below 0.3 (based on model length and freestream velocity), which is consistent with theory. The most significant changes were observed in a critical reduced frequency range between ω R = 0.3 and ω R = 1.5 (scales of 4-20 vehicle lengths, or periods of 0.6 to 3s for a vehicle at 30 m/s). Higher frequencies will have significant effects, but these were observed to show little sensitivity to frequency above the critical range. Small physical features on real vehicles will add importance to smaller, but not larger, scales. The dynamic effects were largely independent of Reynolds number, including for near-inviscid conditions, indicating that the sources of the non-quasi-steady response were not viscous in origin. Increasing yaw amplitude or combining multiple frequency components did not have a summative impact suggesting that it may not be possible to describe vehicle response to transient conditions using linear concepts such as transfer or admittance functions.

Transverse loading and response of long rod penetrators during high velocity plate perforation

This paper describes the development of mechanically coupled engineering models to predict transverse loading and response of long rod penetrators associated with high velocity perforation of thin to moderately thick plates. Test results for L/D = 20 tungsten alloy rods are presented to illustrate the distinct effects of impact yaw and obliquity on terminal ballistic transverse loading and response of rod penetrators. The yaw effects loading model considers the plate cutting contact force that travels down the side of the rod when yaw is sufficient for contact with the edge of the breaching hole. The obliquity effects model addresses transverse loading due to asymmetric pressure relief as the rod approaches the rear surface and exits the plate. In both cases, the loading is presumed to be impulsive and three-dimensional vector relationships are used to account for the complex encounter geometries associated with arbitrary combinations of impact yaw and obliquity. The response model includes predictions of rod deformation and fracture and post-perforation linear and angular velocity vectors of the residual rod. Model predictions are compared with test results for titanium and tungsten alloy rods.

Yaw and spin effects on high‐intensity sound generation and on drag of whistling projectiles

Projectiles containing axisymmetric ring cavities constitute aeroacoustic sources. These produce high‐intensity tones that are used for coding in the simulation of area weapons effects (SAWE) system. Experimental data obtained in a free‐jet facility are presented describing the effects of yaw, spin, and geometric projectile parameters on sound pressure and drag. In general, the sound pressure decreases with increasing yaw angle whereas the drag increases. Spin tends to increase sound‐pressure levels because of a reduction in asymmetry of flow. Drag increases at zero yaw approximately as the 2.5 power of sound wavelength. Drag increase appears to be due to energy loss by sound radiation at low wavelengths and due to wake modification at large wavelengths.

Thermoregulation and the determinants of heat transfer in Colias butterflies.

As a means of exploring behavioral and morphological adaptations for thermoregulation in Colias butterflies, convective heat transfer coefficients of real and model butterflies were measured in a wind tunnel as a function of wind speed and body orientation (yaw angle). Results are reported in terms of a dimensionless heat transfer coefficient (Nusselt number, Nu) and a dimensionless wind speed (Reynolds number, Re), for a wind speed range typical of that experienced by basking Colias in the field. The resultant Nusselt-Reynolds (Nu-Re) plots thus indicate the rates of heat transfer by forced convection as a function of wind speed for particular model geometries.For Reynolds numbers throughout the measured range, Nusselt numbers for C. eurytheme butterflies are consistently lower than those for long cylinders, and are independent of yaw angle. There is significant variation among individual butterflies in heat transfer coefficients throughout the Re range. Model butterflies without artificial fur have Nu-Re relations similar to those for cylinders. Heat transfer in these models depends upon yaw angle, with higher heat transfer at intermediate yaw angles (30-60°); these yaw effects increase with increasing Reynolds number. Models with artificial fur, like real Colias, have Nusselt numbers which are consistently lower than those for models without fur at given Reynolds numbers throughout the Re range. Unlike real Colias, however, the models with fur do show yaw angle effects similar to those for models without fur.The independence of heat loss from yaw angle for real Colias is consistent with field observations indicating no behavioral orientation to wind direction. The presence of fur on the models reduces heat loss but does not affect yaw dependence. The large individual variation in heat transfer coefficients among butterflies is probably due to differences in fur characteristics rather than to differences in wing morphology.Finally, a physical model of a butterfly was constructed which accurately simulates the body temperatures of basking Colias in the field for a variety of radiation and wind velocity conditions. The success of the butterfly simulator in mimicking Colias thermal characteristics confirms our preliminary understanding of the physical bases for and heat transfer mechanisms underlying thermoregulatory adaptations in these butterflies.

Closure to “Yaw Effects on Galloping Instability”

Closure to “Yaw Effects on Galloping Instability”

Discussion of “Yaw Effects on Galloping Instability”

Discussion of “Yaw Effects on Galloping Instability”

Yaw Effects on Galloping Instability

Quasisteady theory of galloping oscillations of slender prismatic structures, such as transmission lines, stay cables, etc. is extended to cover flows approaching at a yaw angle. From the independence principle, aerodynamic forces are found to reduce with the cosine squared of the yaw angle, while dynamic angles of attack increase inversely with the cosine. The combined effects result in a simple universal galloping response characteristic for arbitrary yaw angles, in terms of a dimensionless reduced amplitude and reduced velocity. This depends on the aerodynamic characteristics of the cross section and the mode shape. It is found that yaw shifts the instability towards higher velocities, but lower amplitudes. This, in general, improves the stability of the system, however, hard oscillators consequently also require lower starting amplitudes. Predictions are compared with calculated response characteristics based on measured static data for a yawed D-section and the agreement is fair.

Aerodynamic and Flight Dynamic Analysis of Finned Re-Entry Vehicles

A computational method is presented for predicting nonlinear aerodynamic characteristics of finned re-entry configurations and (by computer simulation) the effect of these characteristics on vehicle flight stability. These aerodynamic characteristics, which include induced roll and yaw effects, are highly dependent on in viscid surface cross-flow. This cross-flow is often severe enough to produce large induced roll moments which can negate the control effect of the fins and in some cases generate severe flight instabilities. The important cross-flow effects on fins are accurately determined by an approximation to the circumferential momentum equation. Particular attention is given to a representation of the fin roll and yaw characteristics with analytic functions of angle of attack and fin cant. Computer simulations indicate that the adverse cross-flow effects for a variable cant, two-fin roll-control system can be dramatically reduced by the addition of two fixed-cant fins. The validity of the analytic methods for fin aerodynamic characteristics and the trajectory simulation technique is fully established by means of a flight test in which the unique four-fin control system maintained vehicle roll and yaw stability through a severe roll resonance encounter. Actual roll rate and flight-derived fin aerodynamic characteristics are in excellent agreement with predictions, thus verifying the analysis.