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Measurements in the aerodynamic boundary layer using heat transfer, hot-film sensors are receiving a significant amount of effort at the Langley Research Center. A description of the basic sensor, the signal conditioning employed, and several manifestations of the sensor are given. Results of a flow reversal sensor development are presented, and future work areas are outlined.
A proposed shear sensor calibrator consists of a rotating wheel with the sensor mounted tangential to the rim and positioned in close proximity to the rim. The shear stress generated by the flow at the sensor position is simply tau(sub omega) = (mu)r(omega)/h, where mu is the viscosity of the ambient gas, r the wheel radius, omega the angular velocity of the wheel, and h the width of the gap between the wheel rim and the sensor. With numerical values of mu = 31 (mu)Pa s (neon at room temperature), r = 0.5 m, omega = 754 /s (7200 rpm), and h = 50.8 m, a shear stress of tau(sub omega) = 231 Pa can be generated. An analysis based on one-dimensional flow, with the flow velocity having only an angular component as a function of the axial and radial coordinates, yields corrections to the above simple formula for the curvature of the wheel, flatness of the sensor, and finite width of the wheel. It is assumed that the sensor mount contains a trough (sidewalls) to render a velocity release boundary condition at the edges of the rim. The Taylor number under maximum flow conditions is found to be 62.3, sufficiently low to obviate flow instability. The fact that the parameters entering into the evaluation of the shear stress can be measured to high accuracy with well-defined uncertainties makes the proposed calibrator suitable for a physical standard for shear stress calibration.
Local heating compensates for conduction of heat from sensors into modules. Two hot-film sensors stacked on wind-tunnel model. Outer sensor detects changes in boundary-layer flow. Inner sensor provides active thermal isolation between outer sensor and model. Thermal boundary condition controlled at response time of detection hot-film sensor, significantly less than response time of internally heated model. Requires less power to maintain outer hot-film sensor at given temperature, enabling system to respond over greater dynamic range before power limits of instrument reached. Stacked sensors bonded to surface of most wind-tunnel models, even to curved surfaces, and removed after completion of experiments.
A micro sized multi-axis semiconductor skin friction/wall shear stress induced by fluid flow. The sensor design includes a shear/strain transduction gimble connected to a force collecting plate located at the flow boundary surface. The shear force collecting plate is interconnected by an arm to offset the tortional hinges from the fluid flow. The arm is connected to the shear force collecting plate through dual axis torsional hinges with piezoresistive torsional strain gauges. These gauges are disposed on the tortional hinges and provide a voltage output indicative of applied shear stress acting on the force collection plate proximate the flow boundary surface. Offsetting the torsional hinges creates a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from small shear stress, or small displacement of the collecting plate. The design also isolates the torsional sensors from exposure to the fluid flow.
Real-time monitoring of water volume fraction in multiphase flows is an important problem for a number of industrial applications. The water phase in the multiphase flows may correspond to either the dispersed phase or the continuous phase. In the past, several lowcost and nonintrusive techniques based on the electrical capacitance tomography (ECT) has been developed to image and monitor in real-time multiphase flows containing water. Furthermore, such monitoring becomes increasingly challenging for high salinity levels, and no reliable ECTbased method is presently available which could work for obtaining water volume fraction in multiphase flows for all water salinity levels. In this paper, we propose a new approach based on the Hanai’s formula for complex dielectric constant and taking advantage of the Maxwell- Wagner-Sillars effect to obtain, to a good approximation, water volume fractions in multiphase flows containing water as either dispersed or continuous phase.
This innovation is a miniature or micro sized semiconductor sensor design that provides two axis direct non-intrusive measurement of skin friction or wall shear stress in fluid flow. The sensor is fabricated by micro-electro-mechanical system (MEMS) technology, enabling small size and low cost reproductions. The sensors have been fabricated by utilizing MEMS fabrication processes to bond a sensing element wafer to a fluid coupling wafer. This layering technique provides for an out of plane dimension that is on the same order of length as the inplane dimensions. The sensor design has the following characteristics: a shear force collecting plate with dimensions that can be tailored to various application specific requirements such as spatial resolution, temporal resolution and shear force range and resolution. This plate is located coplanar to both the sensor body and flow boundary, and is connected to a dual axis gimbal structure by a connecting column or lever arm. The dual axis gimbal structure has torsional hinges with embedded piezoresistive torsional strain gauges which provide a voltage output that is correlated to the applied shear stress (and excitation current) on force collection plate that is located on the flow boundary surface (hence the transduction method). This combination of design elements create a force concentration and resolution structure that enables the generation of a large stress on the strain gauge from the small shear stress on the flow boundary wall. This design as well as the use of back side electrical contacts establishes a non-intrusive method to quantitatively measure the shear force vector on aerodynamic bodies.
The advent of affordable computing, low-cost sensor hardware, and high-speed and reliable communications have spurred installation of ubiquitous sensors in complex engineered systems. However, ensuring reliable data quality remains a challenge. Exploitation of redundancy among sensor signals can help improving the precision of measured variables, detecting the presence of gross errors, and identifying faulty sensors. The cost of sensor ownership, maintenance efforts in particular, can still be cost-prohibitive however. Maximizing the ability to assess and control data quality while minimizing the cost of ownership thus requires a careful sensor placement. To solve this challenge, in this work we develop a generally applicable method to solve the multi-objective sensor placement problem in systems governed by linear and bilinear balance equations. Importantly, the method computes all Pareto-optimal sensor layouts with conventional computational resources and requires no information about the expected sensor quality.
Greater utilization of subsurface reservoirs perturbs in-situ chemical-mechanical conditions with wide ranging consequences from decreased performance to project failure. Understanding the chemical precursors to rock deformation is critical to reducing the risks of these activities. To address this need, we investigated the coupled flow-dissolution- precipitation-adsorption reactions involving calcite and environmentally-relevant solid phases. Experimentally, we quantified (1) stable isotope fractionation processes for strontium during calcite nucleation and growth, and during reactive fluid flow; (2) consolidation behavior of calcite assemblages in the common brines. Numerically, we quantified water weakening of calcite using molecular dynamics simulations; and quantified the impact of calcite dissolution rate on macroscopic fracturing using finite element models. With microfluidic experiments and modeling, we show the effect of local flow fields on the dissolution kinetics of calcite. Taken together across a wide range of scales and methods, our studies allow us to separate the effects of reaction, flow, and transport, on calcite fracturing and the evolution of strontium isotopic signatures in the reactive fluids.
Sensor detects flow reversal in boundary layer. Laminar-separation sensor provides means for detecting laminar-separation bubble by use of very thin, surface-mounted sensor. Consists of flush array of three proximate thin films. Middle film electronically heated by means of constant-temperature anemometer (CTA). Outer films, one upstream and one downstream of middle film, incorporated into bridge circuit to respond as resistance thermometers. This sensor provides only known surface-mounted means for positively identifying pressure of laminar separation as cause of boundary-layer transition.
A floating element shear sensor and method for fabricating the same are provided. According to an embodiment, a microelectromechanical systems (MEMS)-based capacitive floating element shear stress sensor is provided that can achieve time-resolved turbulence measurement. In one embodiment, a differential capacitive transduction scheme is used for shear stress measurement. The floating element structure for the differential capacitive transduction scheme incorporates inter digitated comb fingers forming differential capacitors, which provide electrical output proportional to the floating element deflection.
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Proposed laser/ultrasonic thermometer measures bulk and surface temperatures of part without physical contact. No sensors or wire connections needed on part, moving or stationary. Problems of bonding sensors, of mutal diffusion of materials between sensor and part, and of disturbances of fluid and heat flows by sensor avoided. Single thermometer used to measure many parts remotely.
This innovation is based on advanced multi-dimensional extensions of ECVT sensors that involve ECVT, Displacement Current Phase Tomography (DCPT), Maxwell-Wagner-Sillars polarization effect (MWS), and velocimetry which exploit the variation of electric properties between the oil, water, and gas coming out of the well. Capacitance sensors are embedded on the inside of a pipe spool and placed in-line with the subsea oil line piping on the extraction end of the well. The difference in dielectric, dielectric loss, surface polarization, and velocity of each phase are used in the multi-dimensional algorithm to measure the volume fraction, distribution, velocity, mass flow rate, and flow regime of the mixture moving through the pipe.
The porous microphone in an airfoil is described as a directional sensor which rejects flow noise. The airfoil allows the sensor to be rotated in the airflow over a wide range of yaw angles, 0 to 90 degrees, avoiding flow separation over the surface of the sensor and its associated additional flow noise. The microphone is discussed in terms of its acoustic properties, vibration sensitivity, effect of Mach number on the directivity function, and flow noise. Additional information on the acoustic calibration of the microphone, the acceleration sensitivity of the airfoil, stationary source and receiver in a moving gas, acoustic tests in airflow, and flow noise tests of the airfoil porous surface sensor is included.
The purpose of this article is to present additional information about the flow-velocity sensors described briefly in the immediately preceding article. As noted therein, these sensors can be characterized as artificial hair cells that implement an approximation of the sensory principle of flow-sensing cilia of fish: A cilium is bent by an amount proportional to the flow to which it is exposed. A nerve cell at the base of the cilium senses the flow by sensing the bending of the cilium. In an artificial hair cell, the artificial cilium is a microscopic cantilever beam, and the bending of an artificial cilium is measured by means of a strain gauge at its base (see Figure 1). Figure 2 presents cross sections of a representative sensor of this type at two different stages of its fabrication process. The process consists of relatively- low-temperature metallization, polymer-deposition, microfabrication, and surface-micromachining subprocesses, including plastic-deformation magnetic assembly (PDMA), which is described below. These subprocesses are suitable for a variety of substrate materials, including silicon, some glasses, and some polymers. Moreover, because it incorporates a polymeric supporting structure, this sensor is more robust, relative to its silicon-based counterparts.
The overall goals of this project are divided into 3 important phases. First, a peer-to-peer SCADA network is to be established where identity profile of sensors from fossil-power plants will be stored in an immutable manner in order to verify data flow integrity in real time. Second, it is aimed to develop a Blockchain-based provenance platform to audit equipment operations along with data and process integrity violations. In this phase, various operational rules will be incorporated in the ledger on behalf of the operating sensor so its abnormal use can be easily detected. In addition, it is aimed to achieve provenance when the rate of transactions is exceedingly high, thus enabling to design a scalable provenance scheme that can work in real time when number of data collecting points or sensor units increase in fossil-based power plants. Finally, a working testbed will be developed to integrate the Blockchain platform with sensor-based fossil power plant comprising of Remote Terminal Units (RTU) and SCADA devices. Using multiple Raspberry-PIs mimicking the role of RTUs that are interfaced with multiple sensors devices will be deployed to serve as a critical component of fossil power plant and the performance metrics such as throughput, latency, bootstrapping time, etc., will be evaluated on the testbed.
The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex and lead to low-fidelity results. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear stress, normal stress, and their fluctuations are attractive alternatives. However, most direct-measurement shear sensors are bulky in size or not compatible to fluid flow. A sensor has been developed that consists of a floating plate with folded beam support and an optical grid on the back, combined with a high-resolution optical position probe. The folded beam support makes the floating plate more flexible in the sensing direction within a small footprint, while maintaining high stiffness in the other directions. The floating plate converts the shear force to displacement, and the optical probe detects the plate s position with nanometer resolution by sensing the pattern of the diffraction field of the grid through a glass window. This configuration makes the sensor compatible with liquid flow applications.
The STS-51 initial launch attempt of Discovery (OV-103) was terminated on KSC launch pad 39B on 12 Aug. 1993 at 9:12 AM E.S.T. due to a sensor redundancy failure in the liquid hydrogen system of ME-2 (Engine 2033). The event description and time line are summarized. Propellant loading was initiated on 12 Aug. 1993 at 12:00 AM EST. All space shuttle main engine (SSME) chill parameters and Launch Commit Criteria (LCC) were nominal. At engine start plus 1.34 seconds a Failure Identification (FID) was posted against Engine 2033 for exceeding the 1800 spin intra-channel (A1-A2) Fuel Flowrate sensor channel qualification limit. The engine was shut down at 1.50 seconds followed by Engines 2032 and 2030. All shut down sequences were nominal and the mission was safely aborted. SSME Avionics hardware and software performed nominally during the incident. A review of vehicle data table (VDT) data and controller software logic revealed no failure indications other than the single FID 111-101, Fuel Flowrate Intra-Channel Test Channel A disqualification. Software logic was executed according to requirements and there was no anomalous controller software operation. Immediately following the abort, a Rocketdyne/NASA failure investigation team was assembled. The team successfully isolated the failure cause to an open circuit in a Fuel Flowrate Sensor. This type of failure has occurred eight previous times in ground testing. The sensor had performed acceptably on three previous flights of the engine and SSME flight history shows 684 combined fuel flow rate sensor channel flights without failure. The disqualification of an Engine 2 (SSME No. 2033) Fuel Flowrate sensor channel was a result of an instrumentation failure and not engine performance. All other engine operations were nominal. This disqualification resulted in an engine shutdown and safe sequential shutdown of all three engines prior to ignition of the solid boosters.