Shear Stress Sensor Research Articles

High Reynolds number turbulent wind tunnel boundary layer wall-shear stress sensor

The fluctuating wall-shear stress in a turbulent zero-pressure gradient wind tunnel boundary layer at high Reynolds numbers up to Re Θ = 11,400 is determined by the micro-pillar shear-stress sensor MPS3. The sensor concept has already successfully been applied to liquid fluid flows, where the sensor shows low-pass filter characteristics. The low-pass filter characteristic is favorable especially when turbulent frequencies larger than the damped eigenfrequency of the structure occur. The application in air, however, is critical since the dynamic transfer function of the sensor structures exhibits a strong resonance due to low damping. The current results demonstrate that as long as frequencies of turbulent wall-shear stress fluctuations are below the damped eigenfrequency even a resonant sensor structure can be used to accurately assess the fluctuating wall-shear stress, e.g., in turbulent wind tunnel boundary layers.

토양 물리성 측정을 위한 디지털 장치 개발(I) - 디지털 전단저항 측정장치 -

This study was performed to design and construct a digital soil shear stress sensor in order to replace the conventional devices for measuring soil shear property. The developed digital shear stress measuring device can store measured data with GPS position information as a vector format into a computer. Based on the experiments at various field conditions, the measuring characteristic of the device was quite similar to that of a conventional device, SR-2 that has been a major tool to measure the soil shear property. It was concluded that the digital shear stress measuring device was an effective and comprehensive sensor for measuring soil shear property.

Two microthermal shear stress sensors: surface micromachined and bulk-bonding micromachined

We describe two fabricated microthermal shear stress sensors by antiadhesion surface technology and anodic bulk-bonding technology. Two sensors are based on thermal transfer principles with adiabatic structures. The thermal sensor element is a titanium—platinum alloy resistor sputtered on the top of a low pressure chemical vapor deposited (LPCVD) silicon nitride diaphragm with an adiabatic vacuum cavity underneath. The surface micromachined thermal shear stress sensor uses microbumps on the silicon substrate in the sacrificial layer technology to prevent the silicon nitride diaphragm's stiction to the substrate. Microbumps formed by isotropic silicon etching in HNA (the system HF, HNO3, and HC2H3O2) are arrayed in several points on the silicon substrate with distances of 147 µm in the (200×250)-µm2×1.5-µm vacuum cavity. This cavity is formed by LPCVD silicon nitride film sealing with 30-Pa vacuum degree. The anodic bulk-bonding micromachined thermal shear stress sensor uses bulk silicon substrate etching and anodic bonding to form the (200×250)-µm2×400-µm high aspect ratio cavity with 5×10−2 Pa vacuum degree. The titanium platinum alloy resistor, (5×150)-µm2×0.2 µm, sputtered on the top of the 1.5-µm-thick LPCVD silicon nitride diaphragm with this bonding chamber, has a temperature coefficient of resistance (TCR) value of 0.33%/°C. According to the comparison of the adiabatic characteristics among three cases—a titanium platinum alloy resistor located over the high aspect ratio 5×10−2 Pa vacuum cavity, over the 30-Pa vacuum cavity, and directly on top of the substrate—the first case has the best adiabatic characteristic: the titanium platinum alloy resistor located over the 5×10−2-Pa vacuum cavity has the maximum thermal resistance of 5362 °C/W. Besides the sensor sensitivity performances, it has a comparatively short time constant with value of 0.1 ms under the constant current (CC) mode driving circuit.

Ultra-Low-Powered Aqueous Shear Stress Sensors Based on Bulk EG-CNTs Integrated in Microfluidic Systems

Novel aqueous shear stress sensors based on bulk carbon nanotubes (CNTs) were developed by utilizing microelectrical mechanical system (MEMS) compatible fabrication technology. The sensors were fabricated on glass substrates by batch assembling electronics-grade CNTs (EG-CNTs) as sensing elements between microelectrode pairs using dielectrophoretic technique. Then, the CNT sensors were permanently integrated in glass-polydimethylsiloxane (PDMS) microfluidic channels by using standard glass-PDMS bonding process. Upon exposure to deionized (DI) water flow in the microchannel, the characteristics of the CNT sensors were investigated at room temperature under constant current (CC) mode. The specific electrical responses of the CNT sensors at different currents have been measured. It was found that the electrical resistance of the CNT sensors increased noticeably in response to the introduction of fluid shear stress when low activation current (Lt1 mA) was used, and unexpectedly decreased when the current exceeded 5 mA. We have shown that the sensor could be activated using input currents as low as 100 muA to measure the flow shear stress. The experimental results showed that the output resistance change could be plotted as a linear function of the shear stress to the one-third power. This result proved that the EG-CNT sensors can be operated as conventional thermal flow sensors but only require ultra-low activation power ( ~ 1 muW), which is ~ 1000 times lower than the conventional MEMS thermal flow sensors.

Dynamic calibration technique for the micro-pillar shear-stress sensor MPS3

Based on magnetic excitation a dynamic calibration technique for the micro-pillar shear-stress sensor MPS3, which allows one to determine the local wall-shear stress in turbulent flows by optically measuring the velocity gradient within the viscous sublayer of turbulent flows, is described. The proposed dynamic calibration technique allows one to assess the micro-pillar dynamic response for different flow media up to approximately 10 kHz. The results convincingly agree with the findings of a second-order analytical approximation based on experimentally determined damped eigenfrequencies and damping coefficients. Measurements for different sensor geometries and in various fluids show the sensor to possess transfer functions ranging from a flat low-pass filtered response to strong resonant behavior.

The fabrication and integration of a novel shear stress sensor array and its wind tunnel test

A new generation of micro shear stress sensors and flexible PCB for the general purpose of flow separation detection and control is presented here. A novel MEMS shear stress sensor array featuring integration of discrete micro sensors and polyimide substrate has been developed. Then, CFD (Computational Fluid Dynamics) simulations were performed to estimate the corresponding shear stress distribution within the column cylinder aerofoil at flow conditions are the velocity of 17.3 m/s, which is according to the Re of 1 × 105. In the wind tunnel tests, by disposing the two sensor arrays output signals of the sensors output voltages means and RMS values, the results proved by these flexible arrays could detect the location of the fluid separation point in time.

On the modeling of a MEMS-based capacitive wall shear stress sensor

In this paper, a microcapacitive wall shear stress sensor for the measurement of skin friction is developed. The design objective is to measure wall shear stress in the range of 1.25–2.45kPa in laminar boundary layers. Mechanical behavior of the sensing elements, capacitive variations, and sensor’s static response has been investigated using numerical methods. The governing equation whose solution holds the answer to all our questions about the sensor’s characteristics is the nonlinear elasto-electrostatic equation. The results indicate that with this sensor design it is possible to measure wall shear stress values of 1.25kPa and larger with a maximum uncertainty of 1.13%. Apparently, uncertainty depends on magnitude of wall shear stress. The higher the value of wall shear stress is, the smaller the uncertainty becomes. If we need the sensor to detect wall shear stress values less than 1.25kPa with the same accuracy as cited, it is essential to replace the sensing microplate of the device with a thinner one.

Micro thermal shear stress sensor based on vacuum anodic bonding and bulk-micromachining

This paper describes a micro thermal shear stress sensor with a cavity underneath, based on vacuum anodic bonding and bulk micromachined technology. A Ti/Pt alloy strip, 2μm × 100μm, is deposited on the top of a thin silicon nitride diaphragm and functioned as the thermal sensor element. By using vacuum anodic bonding and bulk-si anisotropic wet etching process instead of the sacrificial-layer technique, a cavity, functioned as the adiabatic vacuum chamber, 200μm × 200μm × 400μm, is placed between the silicon nitride diaphragm and glass (Corning 7740). This method totally avoid adhesion problem which is a major issue of the sacrificial-layer technique.

2-D and 3-D numerical modelling of a dynamic resonant shear stress sensor

Despite the importance of wall shear stress measurements in both fundamental and applied fluid dynamic problems, sensors for this application suffer from several shortcomings. A new class of wall shear stress sensor concept that addresses these shortcomings is studied numerically. The properties of a dynamic resonant shear stress sensor are determined using a specially-developed two-dimensional unsteady boundary layer code and a commercially available three-dimensional fluid model. Several characteristics of the sensors are determined using these models including: static sensitivities with and without pressure gradients, sensor design parameter effects. These results indicate that low amplitude, high resonant frequency operation associated with small sensors will have optimum performance. These results also suggest that a MEMS implementation of this sensor should provide the capability of measuring wall shear stress fluctuations in turbulent flows.

Working Principle Simulations of a Dynamic ResonantWall Shear Stress Sensor Concept.

This paper discusses a novel dynamic resonant wall shear stress sensor concept based on an oscillating sensor operating near resonance. The interaction between the oscillating sensor surface and the fluid above it is modelled using the unsteady laminar boundary layer equations. The numerical experiment shows that the effect of the oscillating shear stress is well correlated by the Hummer number, the ratio of the steady shear force caused by the outside flow to the oscillating viscous force created by the sensor motion. The oscillating shear stress predicted by the fluid model is used in a mechanical model of the sensor to predict the sensor's dynamic motion. Static calibration curves for amplitude and frequency influences are predicted. These results agree with experimental results on some extent, and shows some expectation for further development of the dynamic resonant sensor concept.

Dynamic wall-shear stress measurements in turbulent pipe flow using the micro-pillar sensor MPS 3

The micro-pillar wall-shear stress sensor MPS 3 has been used to measure the dynamic wall-shear stress in turbulent pipe flow. The sensor device consists of a flexible micro-pillar which extends from the wall into the viscous sublayer. The pillar-tip deflection caused by the exerting fluid forces serves as a measure for the local wall-shear stress. The pillar is statically calibrated in linear shear flow. A second-order estimate of the pillar dynamic response based on experimentally determined sensor characteristics shows the potential of the present sensor configuration to also measure the dynamic wall-shear stress. The quality of the micro-pillar shear stress sensor MPS 3 to correctly determine the skin friction will be shown by measuring the wall friction in a well-defined fully developed turbulent pipe flow at Reynolds numbers Re b based on the bulk velocity U b and the pipe diameter D in the range of Re b = 10 , 000 – 20 , 000 . The results demonstrate a convincing agreement of the mean and dynamic wall-shear stress obtained with the MPS 3 sensor technique with analytical, experimental, and numerical results from the literature.

Deciphering the Endothelial Shear Stress Sensor

The single nonmotile primary cilium, protruding several microns from the apical surface, contains cytoskeletal elements in a specific fashion. It consists of 9 circularly arranged microtubule doublets, as revealed by transmission electron microscopy,1 but lacks the central ones characteristic for motile cilia and flagellae. The primary cilium is anchored to the basal body and is thereby connected to the cytoskeletal apparatus. Sorokin1 concluded that primary cilia were probably vestigial remnants of motile cilia. We now know that ciliary functions are abundant. Examples include processes involving Hedgehog and Wnt signaling2 and determining left–right asymmetry.3 Cilia functioning as sensory antennas in insect ears and the human retina are well established.4 Because of the widespread presence of primary cilia, it does not come as a surprise that many diseases, often syndromic, are caused by ciliary dysfunction. Several diseases are related to disruption of intraflagellar transport in the case of mutation in, for example, Polaris, Kif3a or various Bbs proteins that can lead to such conditions as obesity and Bardet Biedl Syndrome.5 Other cilium-related proteins involve cell membrane–bound calcium channels such as the complex formed by polycystin-1 and -2, encoded from Pkd1 and Pkd2 , respectively. Mutations cause polycystic kidney diseases.6,7 Article p 1161 Primary cilia were first described in the cardiovascular system in human embryos and adults more than 20 years ago.8 The geometry of the heart and vascular tree strongly influences hemodynamics with repercussions on the pattern of ciliation. Endothelial ciliation is restricted to areas of low and oscillatory …

Boundary Layer Transition on the High Lift T106A Low-Pressure Turbine Blade With an Oscillating Downstream Pressure Field

This paper presents the results of an experimental study of the interaction between the suction surface boundary layer of a cascade of low-pressure (LP) turbine blades and a fluctuating downstream potential field. A linear cascade equipped with a set of T106 LP turbine blades was subjected to a periodic variation of the downstream pressure field by means of a moving bar system at low-speed conditions. Measurements were taken in the suction surface boundary layer using 2D laser Doppler anemometry, flush-mounted unsteady pressure transducers and surface shear stress sensors. The Reynolds number, based on the chord and exit conditions, was 1.6×105. The measurements revealed that the magnitudes of the suction surface pressure variations induced by the oscillating downstream pressure field, just downstream of the suction peak, were approximately equal to those measured in earlier studies involving upstream wakes. These pressure field oscillations induced a periodic variation of the transition onset location in the boundary layer. Two turbulence levels were investigated. At a low level of inlet freestream turbulence of 0.5%, a separation bubble formed on the rear part of the suction surface. Unsteady measurements of the surface pressure revealed the presence of high-frequency oscillations occurring near the start of the pressure recovery region. The amplitude of these fluctuations was of the order of 7–8% of exit dynamic pressure, and inspection of the velocity field revealed the presence of Kelvin-Helmholtz-type shear layer vortices in the separated free shear layer. The frequency of these shear layer vortices was approximately one order-of-magnitude greater than the frequency of the downstream passing bars. At a higher inlet freestream turbulence level of 4.0%, which is more representative of real engine environments, separation was prevented by an earlier onset of transition. Oscillations were still observed in suction surface shear stress measurements at a frequency matching the period of the downstream bar, indicating a continued influence on the boundary layer from the oscillating pressure field. However, the shear layer vortices seen in the lower turbulence intensity case were not so clearly observed, and the maximum amplitude of suction surface pressure fluctuations was reduced.

The development of the heart and microcirculation: role of shear stress

It is evident that hemodynamic factors have a dominant function already during early cardiogenesis. Flow and ensuing shear stress are sensed by endothelial cells by, ciliary modified, cytoskeletal deformation which then activates a number of subcellular structures and molecules. Shear stress dependent changes mostly converge towards NF kappa B signaling and DNA binding, thereby altering metabolic paths and influencing differentiation of the cells. Geometry of the vascular system heavily affects the flow and shear patterns, as is the case in the adult vasculature where atheroprone areas nicely coincide with the frequency of the primary cilium as shear stress sensor.

Recent Innovations in Wall Shear Stress Sensor Technologies

Over the past decade significant improvements have been made in wall shear stress (WSS) sensor technologies. Due to the need to resolve flow structures on the order of 100 μm at frequencies up to 10 kHz, classes of microelectromechanical (MEMS) sensors have been developed to overcome these limitations. Three main classes exist, including floating element, thermal, and optical MEMS flow sensors. A handful of new patents have been issued in all three of these classes. For floating element MEMS flow sensors recent US patents. For thermal MEMS flow sensor. Floating element sensors have the advantage that they provide a direct measurement, while thermal sensors use an empirical formulation based upon the heat transfer from the sensor to the flow. Floating element sensors suffer from error associated with pressure gradients, cross-axis sensitivity to acceleration and vibration inputs, and fabrication issues including misalignment between the floating element and gap, debris becoming trapped in the gap between the floating element and the sensor mount and a compromise between durability and sensitivity. Thermal sensors are more mature as they are based on well established methods; however, the major flaw with this technique is the difficulty associated with minimizing heat transfer between the sensing element and the substrate. The third class of sensors, optical MEMS flow sensors, are quickly emerging as perhaps the most accurate and reliable of the three techniques.

21422 SOIを用いた熱膜式マイクロせん断応力センサの開発(MEMS,OS.1 機械工学が支援する微細加工技術(半導体・MEMS・NEMS),学術講演)

21422 SOIを用いた熱膜式マイクロせん断応力センサの開発(MEMS,OS.1 機械工学が支援する微細加工技術(半導体・MEMS・NEMS),学術講演)

Mean wall-shear stress measurements using the micro-pillar shear-stress sensor MPS3

A new sensor to measure the mean turbulent wall-shear stress in turbulent flows is described. The wall-shear stress sensor MPS3 has been tested in a well-defined fully developed turbulent pipe flow at Reynolds numbers Reb based on the bulk velocity Ub and the pipe diameter D in the range of Reb = 10 000–20 000. The results demonstrate a convincing agreement of the mean wall-shear stress obtained with the new sensor technique with analytical and experimental results from the literature. The sensor device consists of a flexible micro-pillar that extends from the wall into the viscous sublayer. Bending due to the exerting fluid forces, the pillar-tip deflection serves as a measure for the local wall-shear stress. The sensor concept, calibration techniques, the achievable accuracy and error estimates, the fields of application and the sensor limits will be discussed. Furthermore, a first estimate of the pillar dynamic response will be derived showing the potential of the sensor to also measure the turbulent fluctuating wall-shear stress.

Flow control with active dimples

AbstractThe long-term goal is to design and manufacture optimal ‘on-demand’ vortex generators, ‘dimples’ that can produce vortices of prescribed strength and duration for the real-time control of aerodynamic flows that are either undergoing transition or are fully turbulent, attached or separating. Electro-active polymers (EAP) are ideal for a dimple control surface, offering high strain rate, fast response, and high electromechanical efficiency. EAP can also be used as the basis of a resistanc – or capacitance – change pressure sensor, development of which has just begun. In terms of manufacture, inkjet printing of EAP also offers a paradigm shift such that a monolithic control surface is a very real possibility. Important features for integration into a control system are robustness and a predictable, repeatable motion. With these objectives in mind, the suitability of EAP-based actuators is assessed both mechanically and aerodynamically. The ultimate goal is to integrate these devices, along with shear-stress and pressure sensors and distributed control, also under development, into a flexible ‘smart skin’ which could be incorporated into an airframe structure. The response of a laminar boundary layer to forcing is investiagted using mechanical dimples.

Endothelial primary cilia in areas of disturbed flow are at the base of atherosclerosis

Atherosclerosis develops in the arterial system at sites of low as well as low and oscillating shear stress. Previously, we demonstrated a shear-related distribution of ciliated endothelial cells in the embryonic cardiovascular system and postulated that the primary cilium is a component of the shear stress sensor, functioning as a signal amplifier. This shear-related distribution is reminiscent of the atherosclerotic predilection sites. Thus, we determined whether a link exists between location and frequency of endothelial primary cilia and atherogenesis. We analyzed endothelial ciliation of the adult aortic arch and common carotid arteries of wild type C57BL/6 and apolipoprotein-E-deficient mice. Primary cilia are located at the atherosclerotic predilection sites, where flow is disturbed, in wild type mice and they occur on and around atherosclerotic lesions in apolipoprotein-E-deficient mice, which have significantly more primary cilia in the aortic arch than wild type mice. In addition, common carotid arteries were challenged for shear stress by application of a restrictive cast, resulting in the presence of primary cilia only at sites of induced low and disturbed shear. In conclusion, these data relate the presence of endothelial primary cilia to regions of atherogenesis, where they increase in number under hyperlipidemia-induced lesion formation. Experimentally induced flow disturbance leads to induction of primary cilia, and subsequently to atherogenesis, which suggests a role for primary cilia in endothelial activation and dysfunction.

Flight Control Using Synthetic Jets on a Cessna 182 Model

The application of active flow control via synthetic jet actuators for separation and roll control on a scaled Cessna 182 model was investigated experimentally in a low-speed wind tunnel. The model was instrumented with either ailerons or synthetic jets embedded within the outer portion of the wings' span, in lieu of ailerons. Force and moment measurements were performed for various aileron deflections and synthetic jet momentum coefficients (on either both wingtips or only on one). The sensor's rms output was monitored in real time by a computer. When the rms reached a predetermined threshold value, the computer automatically turned on the synthetic jet actuators. Using the appropriate threshold value resulted in complete avoidance of wingtip stall at the angle of attack where separation would have occurred. In addition, the shear stress sensor and wind tunnel force data were used to identify the system dynamics