L. Scott Miller

Exploratory Study of Aircraft Wake Vortex Filaments in a Water Tunnel

The meandering nature of a single vortex filament is examined. The flowfield is typical of that in the vicinity of an aircraft wing tip vortex. Self-induced motion of the vortex filament is examined within the confines of potential flow theory and is compared with experimentally obtained results. A single-sensor constant temperature anemometer is used to measure the amplitude and rate of growth of vortex meandering experimentally. Data are presented that show the variation of the core radius with distance downstream of the point of origin as a function of the vortex strength. Also, experimental data are presented to show the variation in the amplitude of wandering downstream of the point of origin. Using the velocity fluctuations in the close proximity of a vortex filament, it is shown that 1) this quantity grows with downstream distance from the point of origin and 2) the degree of wandering depends on the vortex strength

Effect of Canards on Delta Wing Vortex Breakdown During Dynamic Pitching

The effect of a canard on delta wing vortices was investigated in the 2 3 3 ft water tunnel at Wichita State University. It is well known that the leading-edge vortices generated by a delta-shaped wing greatly enhance a vehicle’ s performance at high angles of attack. In this experiment, different canards were placed in front of a 70-deg swept main delta wing. Dye e ow visualization was used to observe the vortex breakdown location during dynamic pitch-up and pitch-down motion with varying pitch rates. Compared to the no-canard cone guration, results showed that there was a delay in vortex breakdown because of the presence of the canard and the dynamic pitch motion. The most favorable delay was obtained when the canard was located closest to the main delta wing and the model was pitched up at a fast rate or pitched down at a slow rate. Complete vortex breakdown on the main delta wing (i.e., full stall ) occurred at 53 deg for the static case without canard. In comparison, complete vortex breakdown occurred past 90 deg when a canard cone gured delta wing was pitched up at the fastest rate tested (i.e., k = 0.2).

Unsafe at Any (Wind) Speed

The goal of this research was to examine the relative safety and stability of stationary motor vehicles exposed to severe winds. The focus was on private passenger vehicles. 1) The behavior of two instrumented storm-chase vehicles that were exposed to severe winds, 2) the behavior of 291 vehicles exposed to a tornado, and 3) the wind speed required to upset a sedan and a minivan exposed to winds in a wind tunnel were studied. A wind as strong as 47 m s−1 (105 mph) has been measured by a storm-chase pickup truck and 44 m s−1 (98 mph) by a storm chase sedan. The vehicles were not adversely affected by the wind. Also studied were 291 vehicles parked outdoors at homes struck by tornadoes, and the behavior of the vehicles was compared to the F-scale damage to the house. At sites with F1 or F2 damage, 72% of the vehicles were not moved by the wind and 96% were not tipped over. At sites with F3 or F4 damage, 50% were not moved by the wind and 82% were not tipped over. Wind tunnel tests on a sedan and minivan sho...

A conceptual study of airfoil performance enhancements using CFD

A conceptual study of performance enhancing devices for an airfoil is performed using Computational Fluid Dynamics. Two simple, passive devices are examined to explore alternate methods for stall control and lift-to-drag improvement. The motivation behind this research is to study effective techniques to improve performance with fewer drawbacks than previously existing methods. An evaluation scheme is presented to compute airfoil lift, drag and pitching moment for a range of angles-of-attack up to stall. NACA 641-212 singleelement and slatted airfoil CFD results are compared with experimental data to validate the computational model. Evaluations on the first conceptual design (Stall vane) show elimination of the separation at 15 degrees of angle-of-attack where the flow reversal normally starts at 86% - chord. A total drag increase of 22% is detected because of the sharp leading-edge of the device, but the main element drag has a reduction of 43%. The maximum lift coefficient does not show a significant change on the same model. The second device (Dimples) demonstrates the potential of lift-to-drag ratio improvement at the higher angle-of-attack. Further investigation is required to verify the results since the improvement is small.

A Preliminary Database for Low Reynolds Number Propeller Performance Validations

Validation is the essential process of evaluating the precision and reliability of analytical or computational solutions. A series of preliminary propeller wind tunnel tests are designed for validating propeller design and analysis techniques. This work focuses primarily on small propellers operating at Reynolds numbers in the range of 90,000 to 120,000, which is particularly helpful for unmanned aerial vehicle applications. Details of the propeller geometry is described here; however, experimental apparatus geometries along with test section spatial dimensionality will be presented in future work. An open-source computeraided design (CAD) method was used to create the propeller blades, nacelle, and spinner surface outlines, aiming for easy geometry specification reproduction. A simple propeller design with constant pitch-to-diameter ratio, chord length, and thickness was tested. The propeller with an incremental variable pitch of five degrees was tested at three different angles. In addition to classical propeller performance plots of thrust and torque coefficients and efficiency against the advance ratio, nacelle surface pressure distribution was measured in terms of coefficients at several advance ratios.

Determining critical wind speeds for overturning two types of ambulances and a large city bus

Two types of ambulances and a city bus were modeled in a wind tunnel for the minimum wind speed required to upset the stationary vehicles. The Type I ambulance was vulnerable to upset with wind speeds of 135 to 150 mph on the vehicle over wind angles of 40° to 145°. The Type II ambulance was vulnerable to upset with wind speeds of 140 to 170 mph over wind angles of 30° to 145°. The 40-passenger city bus was vulnerable to upset with wind speeds of 60 to 75 mph over wind angles of 35° to 145°. These results showed ambulances were more stable in high winds than common passenger vehicles, but the city bus was very vulnerable in high winds. Testing showed that moving ambulances can be driven at low speeds in minimal hurricane-force winds without exceeding the upset wind speeds on the vehicles. This information provides guidance for safe operation of these vehicles during high winds including hurricanes, thunderstorms, and extra-tropical cyclones.