Shear Stress Sensor Research Articles

Flexible shear-stress sensor skin and its application to unmanned aerial vehicles

Shear-stress information is of great interest for many fluidic dynamic monitoring/diagnostics application. To obtain such information on non-planar surfaces has long been a significant challenge. This paper describes the development of flexible shear-stress sensor skin and its application on the detection of leading edge flow separation for delta planform unmanned aerial vehicles (UAVs). The sensor skin contains a 1-D array of 36 shear-stress sensors, which can cover the 180° surface of the 1.27 cm diameter semicylindrical UAV leading edge with 5° resolution. The implementation process of the sensor skin is significantly simplified by a packaging scheme based on solder bonding and flexible printed circuit board (PCB). The flexible shear-stress sensor skin in both wind tunnel and real flight tests detected the flow separation along the leading edge successfully.

MIXED CONVECTION INDUCED BY MEMS-BASED THERMAL SHEAR STRESS SENSORS

The effect of buoyancy caused by heat generation from a microelectromechanical system (MEMS)-based thermal shear stress sensor is investigated. Due to the small size and relatively low power consumption of such sensors, the buoyancy effect on the overall flow structure is generally negligible. However, its impact on the flow variables such as shear stresses can be significant because such quantities are local and depend on the gradients of the velocity profile next to the sensor. Due to the small dimension of the MEMS sensor, a multiscale modeling approach is adopted to examine the effect of buoyancy on the velocity and wall shear stress profiles. Full-length channel computations are initially performed with finer resolution near the sensor region. Using the boundary conditions derived from the full-length computations, another simulation is performed concentrating on a small region near the shear stress sensor. Based on the temperature distribution in the region of the sensor, the effective thermal length scale is several times the streamwise dimension of the sensor. For a state-of-the-art MEMS sensor dimension of 200\\,\\mu {\\bf m} , the effect of buoyancy on the accuracy of shear stress measurement can be noticeable.

An approximate amplitude attenuation correction for hot-film shear stress sensors

A correction method, based on experimental results, has been developed to remedy the amplitude attenuation that occurs when statically calibrated hot-film shear stress sensors are used in air. The correction method is necessary in applications where typically two-dimensional arrays of measurement points are needed and other sensors, such as hot wires, cannot be employed. The method was developed with a primary aim of obtaining the correct power spectral density of an ensemble-averaged signature from an array of hot-film shear stress sensors. The hot-film sensors are corrected by comparing their individual power spectral densities to a reference spectrum obtained with a single hot wire, slightly elevated but within the viscous sublayer of the turbulent boundary layer. The method is verified by comparing the corrected hot film’s turbulence statistics, power spectral density, and correlation coefficients with the corresponding results from the hot wire.

Measurements and scaling of wall shear stress fluctuations

Measurements of velocity and wall shear stress fluctuations were made in an external turbulent boundary layer developed over a towed surface-piercing flat plate. An array of eight flush-mounted wall shear stress sensors was used to compute the space-time correlation function. A methodology for in situ calibration of the sensors for ship hydrodynamic applications is presented. The intensity of the wall shear stress fluctuations, τ rms/τ avg was measured as 0.25 and 0.36 for R θ =3,150 and 2,160 respectively. The probability density is shown to exhibit positive skewness, and lack of flow reversals at the wall. Correlations between velocity and wall shear stress fluctuations are shown to collapse with outer boundary layer length and velocity scales, verifying the existence of large-scale coherent structures which convect and decay along the wall at an angle of inclination varying from 10 to 13° over the range of Reynolds numbers investigated. The wall shear stress convection velocity determined from narrow band correlation measurements is shown to scale with outer variables. The space-time correlation of the wall shear is shown to exhibit a well-defined convective ridge, and to decay 80% over approximately 3δ for R θ =3,150.

Visualization of Shear Stress With Micro Imaging Chip and Discrete Wavelet Transform

The two-dimensional low-speed structure of a turbulent boundary layer has been clearly visualized by a combination of a shear stress sensor using micro electro mechanical systems and the discrete wavelet transform. The application of two-dimensional discrete wavelet transforms to the visualization of wall shear stress data obtained using the micro shear stress imaging chip is described. The experiment was carried out under various Reynolds number conditions. It is shown that it is possible to visualize the low-speed streak structure as contours of two-dimensional wavelet level corresponding to spanwise wave number as a function of Reynolds number.

Microfabricated Shear-Stress Sensors, Part 3: Reducing Calibration Uncertainty

A calibration procedure for wall shear-stress sensors based on continuum isothermal compressible e ow has been developed. Microfabricated electromechanical e oating element sensors for direct measurement of wall shear stress are chosen for calibration. The calibration equation states a linear relation between the channel height and the calibrated shear stress, resulting in an overall calibration uncertainty as a result of inaccuracy in the channel height measurement. A novel microstrip technique using basic principles of microwave engineering is used to measure the channel height with a high degree of accuracy. The uncertainties involved in the measurement of all of the parameters that are related in any way to the calibration equation are identie ed, measured, evaluated, and integrated into the equation to obtain a complete error analysis of the calibration procedure. The calibration of shear-stress sensors is successfully completed with an overall accuracy of 2%.

Micro-electro-mechanical-systems direct fluid shearstress sensor arrays for flow control

The design and analysis of non-intrusivemicro-electro-mechanical-systems sensors to measure fluid shearstress on the wing surface of a commercial jetliner ispresented. A design specification is derived from analysis offlight loading data using computational fluid dynamics. Thespecification accounts for different flight conditions,aerodynamic smoothness and sensor bandwidth. Capacitive andPZT-based direct fluid shear sensor designs based upon theforce-displacement relationship of a tethered plate are created.The sensors have overall dimensions <0.7 mm, can becollated into large arrays and provide scaled digital outputs, andtheir design methodology is easily generalized to similarapplications.

Characterization of a Silicon-Micromachined Thermal Shear-Stress Sensor

Abstract : A detailed characterization is presented of a silicon-micromachined thermal shear-stress sensor employing a thin-film platinum-sensing element on top of a silicon-nitride membrane that is stretched over a vacuum cavity. The sensor was operated in a constant current mode and characterized using a four-point probe configuration to isolate the sensor response from the effects of external compensation circuitry. The characterization results consist of static sensitivity data at multiple overheat ratios (maximum of 11 mV/Pa at an overheat of 1.0), pressure sensitivity spectra (<1 microvolt/Pa), noise floor spectra (100 nV/square root of Hz), and direct dynamic calibration data (up to 7 kHz). Noise floor measurements reveal a minimum detectable shear stress of 9 microPa/Hz, thus resulting in a sensor dynamic range of over 100 dB (9 microPa 1.7 Pa).

Unsteady Bed Shear Stresses Induced by Navigation: Laboratory Observations

Time-dependent bed shear stresses induced by the passage of a barge tow have been measured with hot film shear stress sensors in a 1:25 scale model. Conditions typical of those observed for Upper Mississippi River navigation traffic were simulated in the experimental facility. Two sets of experiments were carried out: the first set consisted of simultaneous shear stress measurements at different locations for a variety of flow depths and boat operating conditions, providing space-time distributions of ensemble averaged wall shear stresses. The second set included a large number of realizations gathered for one particular flow condition at a single position, allowing analysis of the time evolution of the turbulence characteristics (i.e., standard deviation) of the bed shear stresses. The results of the first set of experiments show that for all the experimental conditions the basic patterns of the shear stress are similar, with two regions of high shear stress associated with the passage of the bow and the...

Characterization of a silicon-micromachined thermal shear-stress sensor

Characterization of a silicon-micromachined thermal shear-stress sensor

Microfabricated shear-stress sensors. III - Reducing calibration uncertainty

Microfabricated shear-stress sensors. III - Reducing calibration uncertainty

The surface hot wire as a means of measuring mean and fluctuating wall shear stress

The paper describes some applications of a wall shear stress sensor technique which is based on hot-wire anemometry. The “surface hot wire” is a flush-mounted thermal resistive wire with a tiny slot underneath. The arrangement of this sensor guarantees an improved signal-to-noise ratio compared to a common surface hot film. The setup and the application of single sensors and of surface hot-wire arrays are shown. Some results are presented that were acquired in several experiments in the field of laminar-turbulent transition.

Dynamic Calibration of a Shear-Stress Sensor Using Stokes-Layer Excitation

The design and implementation of a novel dynamic calibration technique for shear-stress sensors is presented. This technique uses the oscillating wall shear stress generated by a traveling acoustic wave as a known input to the shear-stresssensor.Asilicon-micromachined, eoating-element shear-stresssensorhasbeen dynamicallycalibrated up to 4 kHz using this method. These data represent the e rst broadband, experimental verie cation of the dynamic response of a shear-stress sensor.

A contact-type piezoresistive micro-shear stress sensor for above-knee prosthesis application

A prototype contact-type micro piezoresistive shear-stress sensor that can be utilized to measure the shear stress between skin of stump and socket of above-knee (AK) prosthesis was designed, fabricated and tested. Micro-electro-mechanical system (MEMS) technology has been chosen for the design because of the low cost, small size and adaptability to this application. In this paper, the finite element method (FEM) package ANSYS has been employed for the stress analysis of the micro shear-stress sensors. The sensors contain two transducers that will transform the stresses into an output voltage. In the developed sensor, a 3000/spl times/3000/spl times/300 /spl mu/m/sup 3/ square membrane is formed by bulk micromachining of an n-type [100] monolithic silicon. The piezoresistive strain gauges were implanted with boron ions with a dose of 10/sup 15/ atoms/cm/sup 2/. Static characteristics of the shear sensor were determined through a series of calibration tests. The fabricated sensor exhibits a sensitivity of 0.13 mV/mA-MPa for a 1.4 N full scales shear force range and the overall mean hysteresis error is than 3.5%. In addition, the results simulated by FEM are validated by comparison with experimental investigations.

WS1-2 マイクロせん断応力計によるチャネル乱流の計測と制御(W.S.1 第9回若手研究者・技術者のためのEFDワークショップ : MEMSへの展望)

Measurements of wall shear stress streaks of a turbulent boundary layer in the channel flow were carried out using MEMS-based micro shear stress imaging chip, which contains 85 sensors. The chip is designed and fabricated by surface micromachining technology. One array of 25 micro shear stress sensors in the chip that covers a length of 7.5 mm is used to measure the instantaneous spanwise distribution of the surface shear stress. The statistics of high shear stress streaks were established. Based on the measurement, the physical quantities associated with the high shear-stress streaks, such as their length, width and peak shear-stress level, were obtained.

A219 三次元数値シミュレーションによる熱膜せん断応力センサ周りの流れと熱伝導解析(オーガナイズドセッション4 : 自然対流)

A219 三次元数値シミュレーションによる熱膜せん断応力センサ周りの流れと熱伝導解析(オーガナイズドセッション4 : 自然対流)

Dynamic calibration of a shear-stress sensor using stokes-layer excitation

Dynamic calibration of a shear-stress sensor using stokes-layer excitation

A demonstration of MEMS-based active turbulence transitioning

Abstract At Re=25 000 an active transition to turbulence was demonstrated on a cylinder equipped with flush mounted micro-electro-mechanical-systems (MEMS) shear stress sensor arrays and a thin spanwise slit for internal acoustic perturbations. MEMS hot film sensor arrays measured separation and vortex shedding data which were used to aim and tune acoustic perturbations to the boundary layer; this produced an instability-driven acceleration of the transition process. Perturbations tuned to the instability frequencies (Strouhal number of 2 at Re=25 000 ) and directed at the separation point achieved dramatically higher root-mean-square (RMS) fluctuation levels, thereby delaying separation and reducing wake velocity delicits of the cylinder. Time histories and spectral analysis map the amplification of the input disturbances by the shear layer instability.

A flexible micromachine-based shear-stress sensor array and its application to separation-point detection

A new microfabrication technique has evolved and has been applied to the development of a flexible shear-stress sensor array. The flexible sensor array is composed of many silicon islands that are interconnected by two layers of polyimide film. The silicon islands are formed by RIE etching and contain individual thermal shear-stress sensors. Each sensor on the flexible sensor array has been proven to behave the same as those on a rigid substrate. There are more than 100 sensors distributed inside a 1 cm×3 cm area. The flexible sensor array has a thickness of 80 μm and can be easily attached on a highly curved surface to detect shear-stress distribution. Applications of the flexible sensor array to flow separation-point detection have been demonstrated in this task, including flow over a circular cylinder and instantaneous separation line detection on the rounded leading edges of a delta wing.

Visualization and Detection of Wall Shear Stress using Micro Shear Stress Sensor and Discrete Wavelet Analysis

Shear stress stripe structure on the wall in turbulent boundary layer has been clearly visualized by a combination of a shear stress sensor using MEMS (Micro-Electro-Mechanical-Systems) and discrete wavelets transform. The MEMS shear stress micro chip is designed and fabricated by surface micro-machining technology, contributing to obtaining the time-space two dimensional shear stress data. One array of 25 micro shear stress sensors in the chip that covers a length of 7.5mm is used to measure the instantaneous spanwise distribution of the surface shear stress. The discrete wavelets transform is a software technique to decompose the frequency level with the time and space information of the wave form. In details, the structure in lower Reynolds number is shown clearly on lower frequency wavelets level, the structure in high Reynolds number is done clearly on higher frequency wavelets level. To visualize and detect the high shear stress area more clearly, the frequency levels are recomposed using the multiresolution filtering effect of wavelets transform. The experiments for the shear stress distribution were carried out on Re=8700 and 17400.