High temperature gradient wall shear stress micro-sensors for flow separation control

2018 ◽  
Author(s):  
Cécile Ghouila-Houri ◽  
Quentin Gallas ◽  
Eric Garnier ◽  
Abdelkrim Talbi ◽  
Philippe Pernod ◽  
...  
Keyword(s):  
Shear Stress ◽  
High Temperature ◽  
Temperature Gradient ◽  
Wall Shear Stress ◽  
Flow Separation ◽  
Separation Control ◽  
Flow Separation Control ◽  
High Temperature Gradient ◽  
Wall Shear

scholarly journals High temperature gradient calorimetric wall shear stress micro-sensor for flow separation detection

2017 ◽  
Vol 266 ◽  
pp. 232-241 ◽  
Author(s):  
Cécile Ghouila-Houri ◽  
Quentin Gallas ◽  
Eric Garnier ◽  
Alain Merlen ◽  
Romain Viard ◽  
...  
Keyword(s):  
Shear Stress ◽  
High Temperature ◽  
Temperature Gradient ◽  
Wall Shear Stress ◽  
Flow Separation ◽  
High Temperature Gradient ◽  
Micro Sensor ◽  
Wall Shear

High temperature gradient micro-sensor for wall shear stress and flow direction measurements

2016 ◽  
Vol 109 (24) ◽  
pp. 241905 ◽  
Author(s):  
C. Ghouila-Houri ◽  
J. Claudel ◽  
J.-C. Gerbedoen ◽  
Q. Gallas ◽  
E. Garnier ◽  
...  
Keyword(s):  
Shear Stress ◽  
High Temperature ◽  
Temperature Gradient ◽  
Wall Shear Stress ◽  
Flow Direction ◽  
High Temperature Gradient ◽  
Micro Sensor ◽  
Wall Shear

Development of a MEMS-Based Active Control System for Flow Separation in the Transonic Regime

2000 ◽  
Author(s):  
Steve Tung ◽  
Brant Maines ◽  
Fukang Jiang ◽  
Tom Tsao
Keyword(s):  
Shear Stress ◽  
Control System ◽  
Wind Tunnel ◽  
Flow Separation ◽  
Control Flow ◽  
Separation Control ◽  
Sensors And Actuators ◽  
Trailing Edge ◽  
Flow Separation Control ◽  
Mach Numbers

Abstract A MEMS-based active system is currently under development for flow separation control in the transonic regime. The system consists of micro shear stress sensors for flow sensing and micro balloon actuators for separation control. We have successfully completed the first phase of the program in which the micro sensors and actuators were fabricated and tested in a wind tunnel facility. In the test, the sensors and actuators were flush mounted on a 3D model, which is representative of the upper surface of a wing with a deflected trailing edge flap. The model was installed in the wind tunnel and tested at a series of Mach numbers between 0.2 and 0.6. For all Mach numbers, the sensor output indicates that flow separates over the trailing edge when the micro balloons are in the ‘down’ position. When the micro balloons are inflated, the shear stress level on the trailing edge increases substantially, indicating an improvement of the separation characteristics. This result demonstrates the feasibility of using MEMS sensors and actuators to control flow separation. It is the first step toward the development of a revolutionary closed loop flow control system applicable to existing and future aircraft to enhance aerodynamic performance.

Fabrication, Oxidation and Characterization of Shark Skin Inspired Riblet Structures as Aerodynamically Optimized High Temperature Coatings for Blades of Aeroengines

2010 ◽  
Author(s):  
Claudia C. Bu¨ttner ◽  
Uwe Schulz
Keyword(s):  
Shear Stress ◽  
High Temperature ◽  
Wall Shear Stress ◽  
Physical Vapor Deposition ◽  
Gas Flow ◽  
Turbine Blades ◽  
Picosecond Laser ◽  
Single Digit ◽  
Structured Surfaces ◽  
Wall Shear

This paper deals with the study of different structuring methods for high temperature nickel alloys, which are used for compressor and turbine blades in aeroengines. The ideal structured surface combines high oxidation resistance with low drag in a hot gas flow. The effect of drag reduction due to riblet structured surfaces was originally inspired by the shark scales, which have a drag reducing riblet structure. Riblets were successfully produced on a NiCoCrAlY coating by picosecond laser treatment. This method is suitable for larger structures within the range of some tens of micrometers. Furthermore, experiments were performed by depositing different materials through polymer and metal masks via electrodeposition and physical vapor deposition. All fabricated structures were oxidized at 900–1100°C for up to 100 h to simulate the temperature conditions in an aeroengine. The resulting shape of the riblets was characterized using scanning electron microscopy. The most accurate structures were obtained by using photolithography with a subsequent electrodeposition of nickel. This method is suited for single digit micrometer structures. The reduction of the wall shear stress was measured in an oil channel. The riblet structures prior to oxidation showed a reduction of the wall shear stress of up to 4.9%.

HYDROMAGNETIC FLOW OF A SECOND-GRADE FLUID IN A CHANNEL — SOME APPLICATIONS TO PHYSIOLOGICAL SYSTEMS

1998 ◽  
Vol 08 (08) ◽  
pp. 1323-1342 ◽  
Author(s):  
J. C. MISRA ◽  
B. PAL ◽  
A. S. GUPTA
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Separation ◽  
Asymptotic Series ◽  
Axial Direction ◽  
Second Order ◽  
Second Grade ◽  
Second Grade Fluid ◽  
Grade Fluid ◽  
Wall Shear

An asymptotic series solution for steady flow of an incompressible, second-grade electrically conducting fluid in a channel permeated by a uniform transverse magnetic field is presented. The depth of the channel is assumed to vary slowly in the axial direction. Analytical expressions are derived for the vorticity and pressure drop along the channel as well as the wall shear stress. It is found that for fixed values of the Reynolds number R and the non-Newtonian parameter K1, the wall shear stress increases with increasing value of magnetic parameter M. Numerical computations carried out for a specific slowly varying channel show that flow separation occurs for both second-grade (K1<0) and second-order (K1>0) fluids when |K1|<0.15. The analysis also reveals the interesting result that while flow separation takes place for a second-order fluid for K1≥0.15, no separation occurs at all for |K1|≥0.15 for a second-grade fluid.

Separations and secondary structures due to unsteady flow in a curved pipe

2017 ◽  
Vol 815 ◽  
pp. 26-59 ◽  
Author(s):  
C. Vamsi Krishna ◽  
Namrata Gundiah ◽  
Jaywant H. Arakeri
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Pressure Gradient ◽  
Flow Velocity ◽  
Secondary Flow ◽  
Flow Separation ◽  
Unsteady Flows ◽  
Stress Components ◽  
Wall Shear

Unsteady flows in highly curved geometries are of interest in many engineering applications and also in physiological flows. In this study, we use flow visualization and computational fluid dynamics to study unsteady flows in a highly curved tube ($\unicode[STIX]{x1D6FD}=0.3$) with square cross-section; here, $\unicode[STIX]{x1D6FD}$ is the ratio of the half edge length to the radius of curvature of the tube. To explore the combined effects of curvature and pulsatility, we use a single flow pulse of duration $T$ and peak area averaged axial velocity $U_{p(max)}$, which are independently varied to investigate a range of Dean and Womersley numbers. This range includes cases corresponding to flows in the ascending aorta. We observe radially inward moving secondary flows which have the structure of wall jets on the straight walls; their subsequent collision on the inner wall leads to a re-entrant radially outward moving jet. The wall jet arises due to an imbalance between the centrifugal force and the radial pressure gradient. During the deceleration phase, the low-axial-momentum fluid accumulated in the jet reverses direction and leads to flow separation near the inner wall. We use boundary layer equations to derive scales, which have not been reported earlier, for the secondary flow velocities, the wall shear stress components and the distance ($\hat{P}$) traversed by the secondary flow structures in the transverse plane. We show that $\hat{P}$ predicts the movement of vortical structures until collision. In the limit $\unicode[STIX]{x1D6FD}\rightarrow 0$, the Reynolds number based on this secondary flow velocity scale asymptotes to the secondary streaming Reynolds number proposed by Lyne (J. Fluid Mech., vol. 45 (01), 1971, pp. 13–31) in loosely curved pipes. The magnitude of the secondary flow velocity is high and ${\sim}40\,\%$ of $U_{p(max)}$ for physiological flow conditions. We show that the flow separation on the inner wall has origins in the secondary flow, which was reported in a few earlier studies, and is not due to the axial pressure gradient in the tube as proposed earlier. The wall shear stress components, hypothesized to be important in arterial mechanobiology, may be estimated using our scaling relations for geometries with different curvatures and varying pulsatilities.

Inflow Conditions and the Wall Shear Stress Characteristics of a Biofluid in Separated and Reattached Flow Regions

2014 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Yield Stress ◽  
Human Blood ◽  
Flow Separation ◽  
Shear Thinning ◽  
Vortex Center ◽  
Wall Shear ◽  
Separated And Reattached Flow ◽  
Inflow Conditions

The influence of inflow conditions and human blood rheology on the wall shear stress distribution in a confined separated and reattached flow region is investigated. The governing mass and momentum conservation equations along with the Herschel-Bulkley rheological model are solved numerically using a finite-difference scheme. A parametric study is performed to reveal the influence of uniform and fully-developed inflow velocity profiles on the wall shear stress (WSS) characteristics using hemorheological models that account for the yield stress and shear-thinning non-Newtonian characteristics of human blood. The highest WSS or WSSmax, is always observed inside the flow separation region at a location corresponding to that of the corner vortex center. Uniform inflow results in higher WSSmax values in comparison with fully-developed inflow for moderate upstream flow restrictions. The opposite trend is observed for severe flow restrictions. Uniform inflow always results in smaller flow separation regions and WSSmax values at locations closer to the flow restriction plane. The yield shear-thinning hemorheological model always results in the highest observed peak WSS. The yield stress impact on WSS distribution is most pronounced in the case of severe restrictions to the flow.

scholarly journals Wall Shear Stress Calorimetric Micro-Sensor Designed for Flow Separation Detection and Active Flow Control

Proceedings ◽  
2017 ◽  
Vol 1 (4) ◽  
pp. 376 ◽  
Author(s):  
Cécile Ghouila-Houri ◽  
Quentin Gallas ◽  
Eric Garnier ◽  
Alain Merlen ◽  
Romain Viard ◽  
...  
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Flow Control ◽  
Flow Separation ◽  
Active Flow Control ◽  
Micro Sensor ◽  
Wall Shear ◽  
Active Flow

scholarly journals High temperature gradient micro-sensors array for flow separation detection and control

2019 ◽  
Vol 28 (12) ◽  
pp. 125003
Author(s):  
Cécile Ghouila-Houri ◽  
Abdelkrim Talbi ◽  
Romain Viard ◽  
Quentin Gallas ◽  
Eric Garnier ◽  
...  
Keyword(s):  
High Temperature ◽  
Temperature Gradient ◽  
Flow Separation ◽  
High Temperature Gradient ◽  
Sensors Array ◽  
And Control
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