The Stanton gauge technique provides an indirect method for measurement of skin friction on a smooth aerodynamic surface in which a pressure tap is available. This thesis presents the design and evaluation of a new type of skin friction measurement gauge based on the Stanton gauge concept but not requiring a surface pressure tap. This new skin friction measurement gauge, called a "Flow Tab", can therefore be used on an aerodynamic model or aircraft surface without alteration of the surface. The Flow Tab is thus particularly well-suited to use with Cal Poly's Boundary Layer Data System (BLDS), a small, self-contained instrument that can be installed onto a model or aircraft surface without permanent alteration of the surface. A series of preliminary experiments conducted in a low-speed wind tunnel on a flat plate model with mild favorable pressure gradient, with both laminar and turbulent boundary layers, led to selection of three variants of the Flow Tab design. These Flow Tabs had edge heights of 0.002, 0.0035, and 0.005 inches, giving dimensionless heights h+ of 1.4 -16 over the streamwise Reynolds number range of about 0.7 to 2.2 million. Uncertainty analysis and test results demonstrated that better than 10% measurement uncertainty for the Flow Tab results could be achieved with edge heights of 0.0035 and 0.005 inches using the same calibration equations as published for the Stanton gauge. Further investigation of its performance over a wider range of Reynolds numbers, and in more complex conditions including those encountered on swept wings with a variety of pressure gradients, is recommended. Integration of the flow tab with BLDS for flight testing applications presents challenges related to its relatively small pressure signal that may require some special modifications to existing BLDS hardware and software.

Hot-wire anemometry has been routinely employed for laboratory measurements of turbulence for decades. This thesis presents a hot-wire anemometer suitable for use with the Boundary Layer Data System (BLDS). BLDS provides a unique platform for in- flight measurements because of its small, self-contained, robust design and flexible architecture. Addition of a hot-wire anemometer would provide BLDS with a sensor that could directly measure flow velocity fluctuations caused by turbulence. Hot-wires are commonly operated in constant-temperature mode for high frequency response, but require a carefully tuned bridge. The constant-voltage anemometer (CVA) uses a simple op-amp circuit to improve frequency response over constant-current operation. Due to its balance between ease of operation and performance, a CVA system built for this project was tested with a 3.8 micron diameter, platinum-coated tungsten probe. The CVA was calibrated in a steady jet and a power-law curve fit accurately represented the calibration data. The CVA successfully measured velocity fluctuations in a turbulent jet, as well as in laminar and tripped turbulent boundary layers over a flat plate in a 110 MPH wind tunnel. CVA frequency response was investigated using a thermal/electrical model, controlled oscillation in a steady flow, and with a square wave test; these three methods showed agreement. The CVA is selected for integration with BLDS.

This Thesis describes the design, assembly, programming, and evaluation of the BLDS-M-RAKE, the newest addition to the family of devices called the Boundary Layer Data System (BLDS). The BLDS-M-RAKE is a continuation of the BLDS-M series of devices, a modular approach with updated electronics for boundary layer measurements. The BLDS-M-RAKE records data from a number of sensors, intended to be routed to an array of probes, or rake. Through preliminary testing, a new flexible manifold design from molded silicone and the hardware used on the RFduino development boards from the BLDS-M proof-of-concept modules were validated for use in the final prototype design. A PCB was designed to house a Simblee System on a Chip (SOC), 11 Honeywell pressure sensors, a microUSB socket, a microSD socket, a DC-DC boost regulator, and two AAA cells. The SOC was then programmed in C++ with the Arduino IDE. The Simblee was programmed to prompt a user over a serial monitor to confirm test parameters from a configuration file and then coordinates the reading and recording of sensor data during a flight test. Problems after assembly did not allow a full evaluation of the board, but the following was concluded: the sleeping board current draw was less than 3 mA and the peak current draw was less than 30 mA. The sensors could be sampled at 100 Hz and recorded to the microSD card. The flexible manifolds molded from silicone are viable for future designs.

To continue the development of the Boundary Layer Data System (BLDS), a constant voltage hot-wire anemometer (CVA) is implemented into the BLDS for flight-testing. The hot-wire anemometer was chosen as an alternative to the traditional pressure probe because of the ability to measure both average velocity and fluctuating velocity within the boundary layer. Previous work done on the benchtop has led to the design of miniaturization, flight-capable hardware for the BLDS. The next step in the development of the BLDS – CVA calls for quantifying the accuracy of the boundary layer measurements measured by the CVA system. To do this, numerous turbulent boundary layer velocity and fluctuating velocity profiles were taken on a flat-plate at various speeds within the Cal Poly 2x2 wind tunnel with both the traditional pressure probe and the CVA. These test resulted showed agreement between the hot-wire and pressure probe data. Once this was completed the new CVA hardware was tested along with the new software that was written for the BLDS – CVA. In addition, due to the limited memory space onboard the BLDS – CVA, an approximation had to be developed to convert the average voltage data from the BLDS – CVA to the average velocity data due to the non-linear calibration function. The approximation developed was able to match the exact values from a traditional calibration. Lastly, due to the inability to perform a laboratory calibration of the hot-wire at altitude, where the conditions differ significantly from the ground conditions, a new procedure for hot-wire calibration was developed. The method developed was validated through wind tunnel testing and a computer thermal/electric model. With the completion of this work, the BLDS – CVA is ready for flight-testing.

This thesis describes the design and evaluation of two devices to be included in the next generation of the family of devices called the Boundary Layer Data System (BLDS). The first device, called the Quasi-Static Strain Data Acquisition System, is a continuation of the BLDS-M series of devices to be known as the Flight Test Data System (FTDS) that uses a modular approach to acquire non-flow, quasi-static mechanical strain measurements. Various breakout boards and development boards were used to synthesize the device, which were housed by a custom PCB board. The system is controlled by the SimbleeTM System on a Chip (SOC), and strain measurements are acquired using the HX711 analog-to-digital converter (ADC), and acceleration measurements are acquired with the ADXL345 accelerometer. The Arduino IDE was used to program and troubleshoot the device. The second device, called the Dynamic Strain Data Acquisition System, is a laboratory proof-of-concept device that evaluates various methods of acquiring dynamic strain measurements that may be used in future FTDS designs. A custom PCB board was designed that houses the microcontroller and the various passive components and ICs used to acquire and store strain measurements. The system is controlled by the Atxmega128A4U microcontroller, and measurements are acquired using the AD7708 external ADC and the on-board ADC of the microcontroller. Atmel StudioTM was used to program the microcontroller in C/C++ and to troubleshoot the device. Both devices were tested extensively under room temperature and low temperature conditions to prove the reliability and survivability of each device. The quasi-static data acquisition system was validated to acquire and store measurements to a microSD card at 10 Hz, with a peak operating current under 60 mA. The dynamic data acquisition system was proven to acquire a thousand measurements at 1 kHz and store the data to a microSD card, with a peak operating current under 60 mA.

The development of the constant voltage anemometer (CVA) for the boundary layer data system (BLDS) has been motivated by a need for the explicit autonomous measurement of velocity fluctuations in the boundary layer. The frequency response of a sensor operated by CVA has been studied analytically and experimentally. The thermal lag of the sensor is quantified by a time constant, MCVA. When the time constant is decreased, the half-amplitude cut-off frequency, fCVA, is increased, thereby decreasing the amount of attenuation during measurements. In this thesis, three main approaches have been outlined in theory and tested experimentally to determine the feasibility and effectiveness of implementing them with CVA to limit attenuation: operation at higher Vw, implementation of software compensation, and utilization of smaller diameter sensors. Operation of CVA at higher voltage results in little improvement in frequency response but is accompanied by increased danger of wire burnout. However, sensors do need to be operated at high wire voltages to be more sensitive to velocity fluctuations and less sensitive to temperature fluctuations, without reaching a temperature high enough for wire burnout. Software compensation of the CVA output has been shown not to be useful for measurements with BLDS. The electrical noise present in the CVA measurement system is amplified by the correction algorithm and creates measurements that are not representative of the fluctuations being measured. Decreasing sensor diameter leads to a significant decrease of MCVA and therefore increase of fCVA. Under similar operating conditions, a 2.5 micron diameter sensor showed less roll off in the frequency spectra (measured higher turbulence intensities) than a 3.8 micron diameter sensor for tests in both a turbulent jet and in a turbulent boundary layer. Smaller sensors are more fragile and have been shown to have a decrease in sensitivity as compared to larger sensors; however, for some applications, the increase in frequency response may be worth the trade-off with fragility and sensitivity.

The primary motivation for this work was to predict the conditions that would yield minimum drag for a small Ram-Air Turbine used to provide a specified power requirement for a small flight test instrument called the Boundary Layer Data System. Actuator Disk Theory was used to provide an analytical model for this work. Classic Actuator Disk Theory (CADT) or Froude’s Momentum Theory was initially established for quasi-one-dimensional flows and inviscid fluids to predict the power output, drag, and efficiency of energy-extracting devices as a function of wake and freestream velocities using the laws of Conservations of Mass, Momentum, and Energy. Because swirl and losses due to the effects of viscosity have real and significant impacts on existing turbines, there is a strong motivation to develop models which can provide generalized results about the performance of an energy-extractor, such as a turbine, with the inclusion of these effects. A model with swirl and a model with losses due to the effects of viscosity were incorporated into CADT which yielded equations that predicted the performance of an energy-extractor for both un-ducted and ducted cases. In both of these models, for this application, additional performance parameters were analyzed including the drag, drag coefficient, power output, power coefficient, force coefficient, and relative efficiency. For the un-ducted CADT, it is well known that the wake-to-freestream velocity ratio of 1/3 will give the maximum power extraction efficiency of 59.3%; this result is called the Betz limit. However, the present analysis shows that reduced drag for a desired power extraction will occur for wake-to-freestream velocity ratios higher than the value of 1/3 which results in maximum power extraction efficiency. This in turn means that a turbine with a larger area than the smallest possible turbine for a specified power extraction will actually experience a lower drag. The model with the inclusion of swirl made use of the Moment of Momentum Theorem applied to a single-rotor actuator disk with no stators, in addition to the laws of Conservation of Mass, Momentum, and Energy from the CADT. The results from the model w/swirl showed that drag remains unchanged while power extracted decreases with the addition of swirl, with swirl effects becoming more severe for tip speed ratios below about 5. As for CADT, reduced drag for a specified power extraction can be achieved when the wake-to-freestream velocity ratio is higher that than which provides maximum power extraction efficiency. The model w/losses due to viscosity incorporated the losses into the Conservation of Energy relationship. The results from the model w/losses showed that there is a distinct wake-to-freestream velocity ratio at which minimum drag for a specified power output is achieved, and that this velocity ratio is usually—but not always—higher than that for which the power extraction efficiency is a maximum. It was concluded that a lower drag for a specified power output of an energy-extractor can usually be achieved at a wake-to-freestream velocity ratio higher than that which produces the v maximum power extraction efficiency. The latter condition, known as the Betz limit for CADT, and which defines the minimum size for a turbine to provide a specified power extraction, is therefore not the correct target design condition to achieve lowest drag for a small Ram-Air Turbine to power BLDS.

Traditionally, the measurement of turbulence has been conducted using hot-wire anemometry. This thesis presents the implementation of a constant voltage hot-wire anemometer for use with the Boundary Layer Data System (BLDS). A hot-wire calibration apparatus has been developed that is capable of operation inside a vacuum chamber and flow speeds up to 50 m/s. Hot-wires operated with a constant-voltage anemometer (CVA) were calibrated at absolute static pressures down to 26 kPa. A thermal/electrical model for a hot-wire and the CVA circuit successfully predicted the measured CVA output voltage trend at reduced pressure environments; however, better results were obtained when the Nusselt number was increased. A calibration approach that required only one measured flow speed was developed to allow autonomous calibrations of a CVA hot-wire. The single-point calibration approach was evaluated through comparison with the experimental data from the vacuum chamber over a range of 14-50 m/s and at pressures from 26 to 100 kPa. The thermal-electrical model was used to make predictions of CVA output voltage and the corresponding flow speed for conditions that could not be replicated within a laboratory. The first set of predictions were made for conditions from 7.5 to 100 kPa, at a constant temperature of 25⁰C, within a flight speed range of 40 to 150 m/s. Single-point calibrations were developed from these predictions. Additionally, the thermal-electrical model was used to predict hot-wire response for a change in temperature of 25⁰C at 26 kPa and the single-point calibration developed for the pressure range 7.5 to 100 kPa was tested for its ability to adjust. The temperature variation at a single pressure of 26 kPa proved that the single-point function was capable of adapting to off-standard temperatures with the largest deviations of +/- 7% in the mid-range velocities. With a temperature drop, the deviations were below 5%. The second set of thermal-electrical predictions involved conditions for altitude from 0 to 18 km at flow speeds from 40 to 150 m/s. A single-point calibration was developed for altitude conditions. Furthermore, to test the single-point calibration the thermal-electrical model was used to predict hot-re response for a temperature variation of 25⁰C at 18 km. The single-point calibration developed for altitude proved that it was capable of adjusting to a temperature variation of 25⁰C with maximum deviations of about 5% at mid-range velocities. It is proposed that the single-point calibration approach could be employed for CVA measurements with the Boundary Layer Data System (BLDS) to allow hot-wire data to be acquired autonomously during flight tests.