No abstract

No abstract

The safe integration of vertical takeoff and landing aircraft (VTOLs) into an urban setting requires careful consideration of the effects of the wind flows through the urban canyon, which are complex and cannot be predicted with the reliability level necessary to enable safe operations. The assessment of wind in the urban canyon is critical to the siting and design of vertiports and safe operations of VTOLs. Vertiport design guidance related to the effects of wind flows in the urban canyon is limited and draws from helipad design guidance. The guidance recommends that wind conditions be assessed across a vertiport, but the guidance does not suggest how the study should be conducted nor does it provide design thresholds for wind. RWDI, the National Research Council Canada and Transport Canada have joined forces to identify and study the wind characteristics that would be important for the aerodynamic performance of VTOL and how these characteristics would be influenced by buildings and structures in the urban environment. In the framework of this research effort, an experimental approach was developed, centered on several sites in Canadian cities, representing a range of urban densities and surrounding topographies, as wind conditions are highly dependent on the built environment, including building footprint, building features, combinations of buildings and the local climatology. The work involved a quantitative approach in which physical models of several urban sites were built, instrumented and tested in boundary layer wind tunnels. In the wind tunnel experiments, "red flag" wind conditions were identified and measured. Detailed data capturing these flow features were collected around roof tops of lower and taller buildings, representing prospective vertiport locations and along prospective flight paths. This paper provides the details of the wind tunnel testing conducted for one of the urban sites; a site with an existing helipad at a hospital and a low-rise parking garage. The wind tunnel measurements were compared to published helipad design thresholds and combined with long term meteorological conditions representative of the site to determine how often vertiport operations will be limited by unfavourable urban wind conditions on an annual basis and by season. The wind tunnel study provides a case study and demonstrates how to evaluate the safety of a vertiport now, based on limited availability of VTOL aerodynamic performance capabilities and into the future as more information becomes available on VTOL performance in turbulent winds.

<div class="section abstract"><div class="htmlview paragraph">Road-vehicle platooning is known to reduced aerodynamic drag. Recent aerodynamic-platooning investigations have suggested that follower-vehicle drag-reduction benefits persist to large, safe inter-vehicle driving distances experienced in everyday traffic. To investigate these traffic-wake effects, a wind-tunnel wake-generator system was designed and used for aerodynamic-performance testing with light-duty-vehicle (LDV) and heavy-duty-vehicle (HDV) models. This paper summarizes the development of this Road Traffic and Turbulence System (RT²S), including the identification of typical traffic-spacing conditions, and documents initial results from its use with road-vehicle models.</div><div class="htmlview paragraph">Analysis of highway-traffic-volume data revealed that, in an uncongested urban-highway environment, the most-likely condition is a speed of 105 km/h with an inter-vehicle spacing of about 50 m. Probability distributions for spacing and road speed were used to identify a range of suitable inter-vehicle spacings to target for wake conditions. Combining these data with previous research activities that examined the characteristics of road-vehicle wakes, three phases of development for the RT²S were undertaken in multiple wind tunnels leading to a system using porous grids and sets of vertically-oriented vanes. Specific grid and vane combinations generate wake shapes, wind-speed deficits, flow-angularities, and turbulence representative of every-day traffic wakes. Lateral positioning of the system and rotation of the vanes provide wake positioning and flow characteristics representing a variety of wake-in-crosswind conditions, while being able to effectively change the lane of the wake-source vehicles.</div><div class="htmlview paragraph">The results of two experiments are presented to document the influence of traffic wakes, via application of the RT²S, on the aerodynamic performance of road vehicles. First, measurements are presented based on the use of a prototype version of the system with a 15%-scale DrivAer fastback model. Drag reductions from 10% to 31% and side-force-coefficient reductions in excess of 50% were observed for the DrivAer model, relative to uniform-flow conditions, for the 13 specific wake-like conditions replicated. The second set of experiments applied the final RT²S design to testing of a 30%-scale tractor-trailer HDV model, which showed drag reductions as high as 15% for an HDV-wake configuration, with drag reductions of 2% measured for a compact-sedan-wake at 50 m effective forward distance, relative to uniform winds. For both sets of experiments, examining wake effects on LDV and HDV models, changes in aerodynamic performance are attributed in large part to reductions in effective dynamic pressure, but surface-pressure measurements indicate that flow-angularity variations also play a role in crosswind conditions.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Conventional assessments of the aerodynamic performance of ground vehicles have, to date, been considered in the context of a vehicle that encounters a uniform wind field in the absence of surrounding traffic. Recent vehicle-platooning studies have revealed measurable fuel savings when following other vehicles at inter-vehicle distances experienced in every-day traffic. These energy savings have been attributed in large part to the air-wakes of the leading vehicles. This set of three papers documents a study to examine the near-to-far regions of ground-vehicle wakes (one to ten vehicle lengths), in the context of their potential influence on other vehicles.</div><div class="htmlview paragraph">Part two of this three-part paper documents the influence of the ambient winds on the development of the wake behind a vehicle. A series of scaled-model wind-tunnel measurements, supplemented by some high-fidelity numerical simulations, based on a Lattice-Boltzmann approach, are presented to examine the effects cross-wind magnitude, by means of changes in yaw angle, on the wakes behind four vehicle shapes: a sedan, an SUV, a pickup truck, a medium-duty vehicle and a heavy-duty vehicle. The influence of road-representative freestream turbulence is also examined.</div><div class="htmlview paragraph">The results of these investigations show that, under yaw conditions, the distinct differences between the wake structures of slant/step-back and square-back shapes, documented in Part 1, are eliminated. At yaw, the moderate-to-far wake region is dominated by a large vortex structure of similar size to the vehicle itself that generates significant sidewash, analogous to the downwash in the wake of a wing in pitch. All vehicle shapes studied demonstrate this vortex structure which increases in strength with yaw angle. For vehicles following in the wake, not only do they experience a wind-speed deficit associated with the wake, but they experience a twisted wind profile with reduced yaw angles near the ground. The introduction of freestream turbulence is shown to generate a large wake with reduced shear, but without changing the dominant flow characteristics.</div></div>