Dissertations / Theses on the topic 'Aerospace measurements'

As aircraft are designed to a greater extent on computers, the need for accurate and fast CFD algorithms has never been greater. The development of CFD algorithms requires experimental data against which CFD output can be validated and from which insight about flow physics can be acquired. Skin friction, in particular, is an important quantity to predict with CFD, and experimental skin friction data sets aid not only with the validation of the CFD predictions, but also in tuning the CFD models to predict specific flow fields. However, a practical experimental technique for collecting spatially and temporally resolved skin friction data on complex models does not yet exist. This dissertation develops and demonstrates a new luminescent oil film skin friction meter which can produce spatially-resolved quantitative steady and unsteady skin friction data on models with complex curvature.

The skin friction acting on the surface of a thin film of oil can be approximated by the expression τ_w =μ _ou_h/h, where μ _o is the dynamic viscosity of the oil, u_h is the velocity of the surface of the oil film, and h is the thickness of the oil film. The new skin friction meter determines skin friction by measuring h and u_h. The oil film thickness h is determined by ratioing the intensity of the fluorescent emissions from the oil film with the intensity of the incident light which is scattered from the surface of the model. When properly calibrated, that ratio provides an absolute oil film thickness value. This oil film thickness meter is therefore referred as the Ratioed-Image Film-Thickness (RIFT) Meter. The oil film velocity u_h is determined by monitoring the evolution of tagged molecules within the oil film: Photochromic molecules are dissolved into the fluorescent oil and a pattern is written into the oil film using an ultraviolet laser. The evolution of the pattern is recorded, and standard cross-correlation techniques are applied to the resulting sequence of images. This newly developed skin friction meter is therefore called the Luminescent Oil Film Flow-Tagging skin friction meter, or the LOFFT skin friction meter. The LOFFT skin friction meter is demonstrated by collecting time-averaged skin friction measurements on NASA's FAITH model and by collecting unsteady skin friction measurements with a frequency response of 600Hz. Higher frequency response is possible and is dependent on the experimental setup.

This dissertation also contributes to the work done on the Global Luminescent Oil Film Skin Friction Meter (GLOFSFM) by noting that the technique could be influenced by ripples at the oil-air interface. An experiment studying the evolution of ripples at the oil-air interface was conducted to determine under what oil film conditions the GLOFSFM can be appropriately applied. The RIFT meter was crucial for this experiment, as it facilitated quantitative distributed oil film thickness measurements during the wind-tunnel run. The resulting data set is rich in content, permitting the computation of mean wavelengths, peak-to-trough ripple heights, wave speeds, and mean thicknesses. In addition to determining under what oil film conditions the GLOFSFM may be applied, this experiment directly determined the oil film conditions under which the velocity of the ripples may be used to proxy the velocity of the oil film surface. The RIFT meter and the ability to determine oil film surface velocity by monitoring ripple velocities admit yet another time-averaged skin friction meter, the Fluorescent-Oil Ripple-Velocity (FORV) skin friction meter. The FORV skin friction meter recovers skin friction as τ _w = μ_ov_rip/H, where v_rip is the velocity of the ripples, and H is the oil film thickness averaged over the thickness fluctuations due to the ripples. The FORV skin friction meter is demonstrated on NASA's FAITH model.

Price, Jennifer Lou. Unsteady Measurements and Computations on an Oscillating Airfoil with Gurney Flaps. (Under the direction of Dr. Ndaona Chokani)The effect of a Gurney flap on an unsteady airfoil flow is experimentally and computationally examined. In the experiment, the details of the unsteady boundary layer events on the forward portion of the airfoil are measured. In the computation, the features of the global unsteady flow are documented and correlated with the experimental observations.The experiments were conducted in the North Carolina State University subsonic wind tunnel on an oscillating airfoil at pitch rates of 65.45 degrees/sec and 130.9 degrees/sec. The airfoil has a NACA0012 cross-section and is equipped with a 1.5% or 2.5% chord Gurney flap. The airfoil is tested at Reynolds numbers of 96,000, 169,000 and 192,000 for attached and light dynamic stall conditions. An array of surface-mounted hot-film sensors on the forward 25% chord of the airfoil is used to measure the unsteady laminar boundary layer separation, transition-to-turbulence, and turbulent reattachment. In parallel with the experiments incompressible Navier-Stokes computations are conducted for the light dynamic stall conditions on the airfoil with a 2.5%c Gurney flap at a Reynolds number of 169,000.The experimental measurements show that the effect of the Gurney flap is to move the separation, transition and reattachment forward on the airfoil. This effect is more marked during the airfoil's pitch-down than during pitch-up. The computational results verify these observations, and also show that the shedding of the dynamic stall vortex is delayed. Thus the adverse effects of dynamic stall are mitigated by the Gurney flap.

Experiments have been conducted using vane-type vortex generators to control flow separation and exit flow distortion in a diffusing duct. The primary purpose is to examine the feasibility of using surface-mounted hot-film sensors to determine the extent of exit flow distortion. The experimental set-up consists of a two-dimensional blow down type wind tunnel with a variable diffuser exit. One diffuser wall is curved to produce a Stratford-like pressure gradient. The wall's placement is adjustable such that the adverse pressure gradient can be adjusted to promote separation. An active vortex generator array that can be placed at three streamwise locations is used to reduce the extent of flow separation and exit distortion.Diffuser surface pressure and exit total pressure measurements are obtained and compared to the hot-film data. The time-averaged mean and rms voltages from the hot-film data are used as indicators of flow separation and exit flow distortion.Results show that, with the use of the vortex generators, high mean voltages and low levels of rms voltage correlate well with improved pressure recovery. Conversely, poorer pressure recovery is associated with lower mean voltages and higher rms values compared to the baseline cases. Increased total pressures at the diffuser exit are accompanied by increases in hot-film mean voltages. These indicate higher shear stresses, which also correspond to increased flow uniformity. Lower variations in the rms voltages compared to the baseline cases also correlated well with improved total pressures at the diffuser exit.

Godkänd; 2013; 20130101 (marmih); Disputation Ämne: Rymdteknik/Space Engineering Opponent: Senior lecturer Suzanne Gray, Dept of Meteorology, University of Reading, Reading, United Kingdom Ordförande: Professor Sheila Kirkwood, Institutionen för system- och rymdteknik, Luleå tekniska universitet, Luleå /Svenska institutet för rymdfysik, Kiruna Tid: Måndag den 11 februari 2013, kl 09.00 Plats: Aula, Institutet för rymdfysik, Kiruna

Accurate unsteady measurements are required for studying the flows in high speed turbomachines, which rely on the interaction between rotating and stationary components. Using statistics of phase locked ensembles simplifies the problem, but accurate frequency response in the 10-100 kHz range significantly limits the applicable techniques. This research advances the state of the art for phase resolved measurement techniques using for high speed turbomachinery flows focusing on the following areas: development, validation, and uncertainty quantification. Four methods were developed and implemented: an unsteady total pressure probe, the multiple overheat hot-wire method, the slanted hot-wire method, and the phase peak yaw hot-wire method. These methods allow for the entire phase locked average flow field to be measured (temperature, pressure, and velocity components, swirl angle, etc.). No trusted reference measurement or representative canonical flow exists for comparison of the phase resolved quantities, making validation challenging. Five different validation exercises were performed to increase the confidence and explore the range of applicability. These exercises relied on checking for consistency with expected flow features, comparing independent measurements, and cross validation with CFD. The combined uncertainties for the measurements were quantified using uncertainty estimates from investigations into the elemental error sources. The frequency response uncertainty of constant temperature hot-wire system was investigated using a novel method of illuminating the wire with a laser pulse. The uncertainty analysis provided estimates for the uncertainty in the measurements as well as showing the sensitivity to various sources of error.

I present the development of instrumentation and methods for the measurement of coastal processes, ocean surface phenomena, and air-sea interaction in two parts. In the first, I discuss the development of a portable scanning lidar (light detection and ranging) system for manned aircraft and demonstrate its functionality for oceanographic and coastal measurements. Measurements of the Southern California coastline and nearshore surface wave fields from seventeen research flights between August 2007 and December 2008 are analyzed and discussed. The October 2007 landslide on Mt. Soledad in La Jolla, California was documented by two of the flights. The topography, lagoon, reef, and surrounding wave field of Lady Elliot Island in Australia's Great Barrier Reef were measured with the airborne scanning lidar system on eight research flights in April 2008. Applications of the system, including coastal topographic surveys, wave measurements, ship wake studies, and coral reef research, are presented and discussed.

In the second part, I detail the development of instrumentation packages for small (18 – 28 kg) unmanned aerial vehicles (UAVs) to measure momentum fluxes and latent, sensible, and radiative heat fluxes in the atmospheric boundary layer (ABL), and the surface topography. Fast-response turbulence, hygrometer, and temperature probes permit turbulent momentum and heat flux measurements, and short- and long-wave radiometers allow the determination of net radiation, surface temperature, and albedo. Careful design and testing of an accurate turbulence probe, as demonstrated in this thesis, are essential for the ability to measure momentum and scalar fluxes. The low altitude required for accurate flux measurements (typically assumed to be 30 m) is below the typical safety limit of manned research aircraft; however, it is now within the capability of small UAV platforms. Flight tests of two instrumented BAE Manta UAVs over land were conducted in January 2011 at McMillan Airfield (Camp Roberts, CA), and flight tests of similarly instrumented Boeing-Insitu ScanEagle UAVs were conducted in April 2012 at the Naval Surface Warfare Center, Dahlgren Division (Dahlgren, VA), where the first known direct flux measurements were made from low-altitude (down to 30 m) UAV flights over water (Potomac River). During the October 2012 Equatorial Mixing Experiment in the central Pacific aboard the R/V Roger Revelle, ship-launched and recovered ScanEagles were deployed in an effort to characterize the marine atmospheric boundary layer structure and dynamics. I present a description of the instrumentation, summarize results from flight tests, present preliminary analysis from UAV flights off of the Revelle, and discuss potential applications of these UAVs for marine atmospheric boundary layer studies.