Kenneth D. Visser

Measurements of Circulation and Vorticity in the Leading-Edge Vortex of a Delta Wing

Cross-wire measurements or the flowfield above a 75-deg flat plate delta wing were performed at a centerline chord Reynolds number or 2.5×10 5 . Surveys normal to the planform yielded velocity held data at incidence angles or 20 and 30 deg for a series of chordwise locations. The distribution of the velocity, axial vorticity, and circulation showed a strong conical behavior upstream of the breakdown region and away from the apex and trailing edge regions. Spanwise velocity and vorticity profiles through the core of the vortex upstream of breakdown were scaled with the local geometry

Numerical Implications of Solidity and Blade Number on Rotor Performance of Horizontal-Axis Wind Turbines

A numerical study was conducted to examine the impact of rotor solidity and blade number on the aerodynamic performance of small wind turbines. Blade element momentum theory and lifting line based wake theory were utilized to parametrically assess the effects of blade number and solidity on rotor performance. Increasing the solidity beyond what is traditionally used for electric generating wind turbines led to increased power coefficients at lower tip speed ratios, with an optimum between 3 and 4. An increase in the blade number at a given solidity also increased the maximum C p for all cases examined. The possibility of a higher aerodynamic power extraction from solidity or blade number increases could lead to a higher overall system power production. Additional advantages over current 5% to 7% solidity, high speed designs would include lower noise, lower cut-in wind speed, and less blade erosion.

Aerial Refueling Implications for Commercial Aviation

Numerical refueling missions were simulated with a 747-400 tanker for three different sized aircraft—a 747-400, a 777-300, and an A318—to examine the impact on payload capability. Simplified performance and economic models were used to optimize the payload improvement with respect to the refuel point. Optimum refuel points for maximum payload improvement resulted in 88, 110, and 111% payload carrying increases for the A318, 777, and 747 respectively. The mission distance location for the optimum refuel point was observed to increase with increasing aircraft weight. A return on investment of less than one year was predicted for the large aircraft, although the optimum economic refuel point did not coincide with the point for maximum payload increase. Additional benefits were identified to include increased revenue to both the manufacturers and the airline operators, in the form of more product options, more revenue flight hours, increased airframe life, and the possibility for improved takeoff performance and noise reduction. The implementation of in-flight refueling is also proposed to lead to second cycle benefits of a revolution in future commercial aircraft conception and design.

Aerodynamic Comparison of Hyper-Elliptic Cambered Span (HECS) Wings with Conventional Configurations

An experimental study was conducted to examine the aerodynamic and flow field characteristics of hyper-elliptic cambered span (HECS) wings and compare results with more conventional configurations used for induced drag reduction. Previous preliminary studies, indicating improved L/D characteristics when compared to an elliptical planform prompted this more detailed experimental investigation. Balance data were acquired on a series of swept and un-swept HECS wings, a baseline elliptic planform, two winglet designs and a raked tip configuration. Seven-hole probe wake surveys were also conducted downstream of a number of the configurations. Wind tunnel results indicated aerodynamic performance levels of all but one of the HECS wings exceeded that of the other configurations. The flow field data surveys indicate the HECS configurations displaced the tip vortex farther outboard of the wing than the Baseline configuration. Minimum drag was observed on the raked tip configuration and it was noted that the winglet wake lacked the cohesive vortex structure present in the wakes of the other configurations.

On adapting a small PM wind Generator for a multiblade, high solidity wind turbine

This paper explores the design space that exists between multiblade, high-solidity water-pumping turbines and modern high-speed two and three-bladed horizontal axis wind turbines (HAWTs). In particular, it compares the features and performance of a small 12-bladed, high-solidity HAWT to that of a modern three-bladed HAWT. It also outlines a procedure for adapting a small PM wind generator, intended for high-speed operation with a three-bladed HAWT for low-speed operation with a 12-bladed, high-solidity HAWT. This is achieved through a detailed analysis of the effects of several minor changes to the nominal design of the machine. The redesigned machine is shown to be capable of delivering rated power at the reduced speed required by the 12-bladed HAWT, while operating at good efficiency. The overall system performance of the 12-bladed HAWT, coupled to the redesigned wind generator, is shown to be satisfactory. Experimental validation is provided.

Solidity and Blade Number Effects on a Fixed Pitch, 50 W Horizontal Axis Wind Turbine

Experimental studies were conducted on a modified Rutland 500 horizontal axis wind turbine to evaluate numerical implications of solidity and blade number on the aerodynamic performance. Wind tunnel data were acquired on the turbine with flat-plate, constant-chord blade sets and optimum-designed blade sets to compare with theoretical trends, which had indicated that increased solidity and blade number more than conventional 3-bladed designs, would yield larger power coefficients, CP. The data for the flat plate blades demonstrated power coefficient improvements as the range of solidities was increased from 7% to 27%, but did not indicate performance gains for increased blade numbers. It was also observed that larger pitch angles decreased the optimum tip speed ratio range significantly with a small (5% or less) change in maximum CP. The optimum-design 3-bladed rotors produced an increased experimental CP as solidity increased, with reduced tip speed ratio, at the optimum operating point. As blade number was increased at a constant solidity of 10% from 3 to 12 blades, aerodynamic efficiency and power sharply decreased, contrary to the numerical predictions and the flat plate experimental results. Low Reynolds numbers and wind tunnel blockage effects limit these conclusions and a full scale prototype rotor is being constructed to examine the results of the numerical and experimental studies using a side-by-side comparison with a commercially available wind turbine at the Clarkson University wind-turbine test site.

A Computational and Experimental Investigation of a Delta Wing with Vertical Tails

The flow over an aspect ratio 1 delta wing with twin vertical tails is studied in a combined computational and experimental investigation. This research is conducted in an effort to understand the vortex and fin interaction process. The computational algorithm used solves both the thin-layer Navier-Stokes and the inviscid Euler equations and utilizes a chimera grid-overlapping technique. The results are compared with data obtained from a detailed experimental investigation. The laminar case presented is for an angle of attack of 20 degrees and a Reynolds number of 500,000. Good agreement is observed for the physics of the flow field, as evidenced by comparisons of computational pressure contours with experimental flow-visualization images, as well as by comparisons of vortex-core trajectories. While comparisons of the vorticity magnitudes indicate that the computations underpredict the magnitude in the wing primary-vortex-core region, grid embedding improves the computational prediction.

Numerical Implications of Spanwise Camber on Minimum Induced Drag Configurations

Lifting line and Euler techniques have indicated that an elliptical planform cambered in the spanwise direction appears to have a lower induced drag than the uncambered, planar configuration, when both of then have identical arc lengths and the same wetted areas. In other words, a wing geometry with a lower projected span than the planar wing, only because of spanwise cambering, has been found to have a lower induced drag than the corresponding planar case. It was also noted that in the Euler solutions the theoretical minimum induced drag was not achieved on a planar configuration without applying a twist distribution. The increased efficiency of the non-planar configuration is due to induced lift and without accounting for this induced lift, the induced drag is larger then that of the corresponding unfolded planar wing. Induced lift and aerodynamic efficiency of the spanwise cambered configuration was observed to increase with reduced aspect ratio.

On adapting a small PM wind generator for a multi-blade, high solidity wind turbine

Summary form only given. This paper explores the design space that exists between multi-blade, high-solidity water-pumping turbines and modern high-speed 2 and 3-bladed horizontal axis wind turbines (HAWTs). In particular, it compares the features and performance of a small 12-bladed, high solidity HAWT to that of a modern 3-bladed HAWT. It also outlines a procedure for adapting a small PM wind generator, intended for high-speed operation with a 3-bladed HAWT, for low speed operation with a 12-bladed, high solidity HAWT. This is achieved through a detailed analysis of the effects of several minor changes to the nominal design of the machine. The redesigned machine is shown to be capable of delivering rated power at the reduced speed required by the 12-bladed HAWT, whilst operating at a good efficiency. The overall system performance of the 12-bladed HAWT coupled to the redesigned wind generator is shown to be satisfactory. Experimental validation is provided.

Drag Reduction of a Tractor-Trailer Using Planar Boat Tail Plates

The use of planar-sided boat tail plates for aft-end drag reduction on a tractor-trailer was studied numerically, experimentally and on a full scale prototype. Parametric wind tunnel tests utilized a 1:15 scale Peterbilt 379 tractor and 48 foot (14.6 m) trailer with cavity plate concepts mounted perpendicular to the trailer base. Yaw angles up to 9 degrees were examined. Qualitative numerical results confirmed a pressure increase on the aft face of the trailer. Model drag increments, obtained at zero yaw and a width-based Reynolds number of 230,000, based on trailer width, indicated reductions in the drag coefficient, based on frontal area, of up to 0.075 or about 9% of the baseline model trailer drag. Removal of the top plate degraded the performance of all devices. Performance also decreased with yaw angle for all plates mounted perpendicular to the trailer base, contrary to devices with angled plates. Devices with shorter angled plates indicated better performance with the top open rather than an open bottom. Drag reduction was more sensitive to plate inset from the trailer edge than to plate length and a zero inset of the bottom plate maximized performance. Two full scale prototypes were road tested, the first utilized rigid composite sides with a flexible top and bottom and the second was an all rigid-sided aluminum design. The former exhibited cross-country road fuel savings of about 0.5 miles per gallon (0.2 kilometers/liter), approximately 9%, over a 10,000 mile (16,093 km) trip, while the latter returned inconclusive results. Estimated fuel savings for a typical 120,000 miles (193,121 km) per year traveled were approximately 1500 gallons (5677 liters) per truck.