William R. Lindberg

Viscous characteristics of a Utah tar sand bitumen

Abstract The viscous behaviour of an extracted tar sand bitumen has been experimentally examined and the results summarized in this Paper. The material studied was from the Asphalt Ridge, Utah area. The viscosity of the bitumen has been determined as a function of temperature (293–422 K), toluene (solvent) content (0–10%), composition (0–14.6% asphaltenes), oxidation and shear history. In all cases studied, the Arrhenius plots were significantly non-linear at temperatures s> 373 K, with viscous behaviour becoming less sensitive to toluene content with increasing temperature. Low temperature behaviour was strongly dependent on toluene content. The presence of asphaltenes in the bitumen was shown to be a strong viscosity enhancer. Oxidation and shear history were also shown to measurably increase the bitumen viscosity.

Measurements of specific heat, thermal conductivity and thermal diffusivity of Utah tar sands

A constant applied heat flux method has been used to measure the specific heat and thermal conductivity of large samples of Utah (North-west Asphalt Ridge) tar sands as a function of temperature. Independent measurements of density allowed for the calculation of thermal diffusivity. Constituent analysis of the tar sand samples also permitted the calculation of bitumen and sand specific heats. Specific heat of the bitumen was found to increase with temperature from 1.85 to 3.9 kJ kg−1 K−1 for temperatures between 300 and 480 K. Specific heat of the sand matrix increased only slightly, from 0.85 to 1.0 kJ kg−1 K− for the same range of temperature. Corresponding thermal diffusivities for tar sand were found to decrease with temperature, and had a range of 5 · 10−7–9 · 10−7 m2 s−1 over the measured temperatures. It was concluded that the latent heat of both bitumen and water have a strong influence on the apparent overall specific heat of tar sand.

Experimental Study of a Resonant Fence Actuator in a Turbulent Boundary Layer

An experimental study was conducted to examine the characteristics of a resonant oscillating fence actuator in a turbulent boundary layer. Experimental tests were conducted on static, transitioning, and oscillating fences at difierent heights and frequencies. As expected, the static fences produced spoiler-like efiects, but the results difiered signiflcantly from earlier studies in laminar boundary layers. Transitioning fences demonstrated that signiflcant disturbances could be created near the fence in times scales small relative to the time scale in the ∞ow. Oscillating fences also produced signiflcant disturbances to the ∞ow in the form of convecting vortices. The peak suction associated with these disturbances scaled with the fence height while the net lift produced scaled with the Strouhal number. Due to the large disturbances produced and the small power requirement, these actuators may be useful in many ∞ow control applications.

Turbulence and the Isolated Wind Turbine

The turbulence in the atmospheric inflow to a wind turbine as well as the turbulence produced by the wind turbine are considered. A good understanding and ability to model this turbulence is critical for designing turbines with higher efficiencies and greater reliability. The atmospheric boundary layer is first discussed broadly followed by a presentation of past and present measurement and modeling efforts. The effects of the atmospheric boundary layer turbulence on wind turbine aerodynamics and aeroelastics are then discussed, and the importance of wake turbulence is considered. Attempts to use control to mitigate the effects of turbulence on the wind turbine are presented, and the extreme challenges of modeling all the relevant scales of turbulence required to accurately model wind turbines is discussed. As each of these items is presented, future needs for bettering our understanding of turbulence relevant to a wind turbine are identified. The presentation of these subjects makes it clear that there is still much to be learned about the turbulence associated with wind turbines that could impact future designs.

Flow Structures Generated by Oscillating Fences in Boundary Layer Flows

An experimental study of the flow structures generated by stationary and oscillating fences in laminar boundary layer flows is reported. Flow visualization in a water tow -tank was used. The central objective of the study was to identify and classify the various flow regimes that are observed for this flow situation. Wit hin the parameter range of the experimental system, the flows past the fence consisted of periodically shed vortical

An Experimental Investigation of Starting Impinging Jets

Impulsively started impinging jets were experimentally investigated in a water tank utilizing a fluorescent dye technique. The jets were examined prior to and subsequent to impingement. The impingement surfaces included a flat surface and a two-dimensional semicircular concave surface. The normalized jet-to-surface distance and the jet Reynolds number were varied. Using digitized flow visualization images, the jet trajectories, front velocities, growth rates, and convective velocities of large-scale turbulent structures were quantified. A central conclusion of this investigation is that for all cases studied, the jet-front velocity varies with the square root of time

Effect of an Oscillating Fence Actuator on a Stationary and Pitch Oscillating Wing

Experiments have been conducted to characterize the ability of a fence actuator to alter the aerodynamic loading of stationary and pitch oscillating wings. In particular, an oscillating fence on a NACA-23012 airfoil has been examined using Particle Image Velocimetry (PIV) and time-resolved pressure measurements. The experiments were designed to study the efiect of actuator frequency and the efiect of angle of attack on the surface pressure footprints and the ∞ow fleld behind the actuator. Experiments over a stationary airfoil show that the fence frequency strongly efiects the evolution of the structures generated by the fence. On both stationary and oscillating airfoils, higher actuation frequencies are more efiective in producing higher suction peaks. For an oscillating airfoil, mean angle of attack variation strongly efiects the baseline pressure distribution. The disturbances, however, remain largely unafiected by the variations in mean angle of attack, showing the limited efiect of airfoil oscillation on the disturbances produced by the fence in the range studied. Integrated lift and moment are used to quantify the efiectiveness of the fence actuator. The su‐ciently large changes produced in the lift and moment coe‐cients show the potential of this device for altering aerodynamic loading of the wing and suppressing ∞utter.

Initial Results of an Experimental Study of Oscillating Fence Actuators on a Stationary and Pitch Oscillating Wing

Initial experiments have been conducted to develop methods to characterize ∞ow behavior past stationary and oscillating airfoils for assessment of oscillating fence actuators. In particular, the oscillating fence on a NACA-23012 airfoil has been examined using Particle Image Velocimetry (PIV) and time resolved pressure measurements. Fences and other actuators (eg. synthetic jets) are attractive alternatives to current methods used for ∞utter suppression due to their low power requirement. Such ∞ows are di‐cult because phase averaged measurements require phase locking on both the airfoil position and the fence position (dual phase locking). A bin averaging technique was validated using oscillating fence on stationary airfoil and was successfully implemented as an alternative to dual phase locking for the case of oscillating fence on oscillating airfoil. Pressure measurements over the stationary airfoil with oscillating fence show the formation of a structure with a footprint very similar to that of a vortex whose strength decays rapidly as it convects downstream. Phase locked PIV measurements show formation of two distinct zones, of positive and negative vorticity, as the fence enters the ∞ow. As the fence retracts the structures detach and decay rapidly. Bin averaged pressure distributions for the oscillating airfoil show that pressure ∞uctuations due to the fence appear to be superimposed on that of the baseline oscillating airfoil with no fence. It was also observed that the magnitude of the pressure ∞uctuations due to the fence depend somewhat on the instantaneous airfoil position but depend little on the direction of oscillation (whether increasing or decreasing fi). PIV measurements showed formation, detachment, and decay of the structures is very similar to those for the stationary airfoil, but the structures are comparatively stronger and convect slower.

Modal Structure of Surface Turbulence Using Low-Order Turbulence Modeling

*† ‡ The use of the Proper Orthogonal Decomposition (POD) to capture turbulence near the surface in an atmospheric turbulent boundary layer is explored. The purpose of this work is to evaluate the possibility of using low-order models based on the POD for simulating such flows. As an example, data for a convectively active boundary layer in October 1999 captured during the CASES 99 study are considered. The results of the analysis performed here indicate that, although the lowest order modes of the fluctuating velocities contain the majority of the energy, it is the next higher modes that are necessary to capture the details of the more extreme events observed. Using only the first several modes, satisfactory representations of the fluctuating velocities and the instantaneous turbulent kinetic energy are obtained.

Numerical Model of a Dynamic Resonant Wall Shear Stress Sensor

A novel dynamic resonant wall shear stress sensor concept based on an oscillating sensor operating near resonance is investigated numerically. The interaction between the oscillating sensor surface and the ∞uid above it is modelled using the unsteady boundary layer equations. The simulations show that the oscillating shear stress on the sensor surface due to its motion lags the sensor’s motion and is responsible for the sensitivity of the sensor to shear stress. Over a wide range of conditions, the efiect of the oscillating shear stress is well correlated by the Hummer number, the ratio of the steady shear force caused by the outside ∞ow to the oscillating viscous force created by the sensor motion. The oscillating shear stress predicted by the ∞uid model is used in a mechanical model of the sensor to predict the sensor’s dynamic motion. The results of the mechanical model show that the additional shear force causes a reduction in the oscillation amplitude, and the reduction monotonically increases. A static calibration curve is predicted that indicates that the sensor’s amplitude decreases non-linearly with increasing shear stress. These results agree qualitatively with experimental results, and thus the model provides a rigorous basis upon which further development of the dynamic resonant sensor can be pursued.