scholarly journals Application of Prandtl’s Theory in the Design of an Experimental Chamber for Static Pressure Measurements

Sensors ◽  
2021 ◽  
Vol 21 (20) ◽  
pp. 6849
Author(s):  
Pavla Šabacká ◽  
Vilém Neděla ◽  
Jiří Maxa ◽  
Robert Bayer
Keyword(s):  
Supersonic Flow ◽  
Laval Nozzle ◽  
Pressure Sensors ◽  
Small Diameter ◽  
Correct Choice ◽  
Primary Electron ◽  
Experimental Chamber ◽  
State Variables ◽  
Vacuum Chambers ◽  
Low Pressures

Pumping in vacuum chambers is part of the field of environmental electron microscopy. These chambers are separated from each other by a small-diameter aperture that creates a critical flow in the supersonic flow regime. The distribution of pressure and shock waves in the path of the primary electron beam passing through the differentially pumped chamber has a large influence on the quality of the resulting microscope image. As part of this research, an experimental chamber was constructed to map supersonic flow at low pressures. The shape of this chamber was designed using mathematical–physical analyses, which served not only as a basis for the design of its geometry, but especially for the correct choice of absolute and differential pressure sensors with respect to the cryogenic temperature generated in the supersonic flow. The mathematical and physical analyses presented here map the nature of the supersonic flow with large gradients of state variables at low pressures at the continuum mechanics boundary near the region of free molecule motion in which the Environmental Electron Microscope and its differentially pumped chamber operate, which has a significant impact on the resulting sharpness of the final image obtained by the microscope. The results of this work map the flow in and behind the Laval nozzle in the experimental chamber and are the initial basis that enabled the optimization of the design of the chamber based on Prandtl’s theory for the possibility of fitting it with pressure probes in such a way that they can map the flow in and behind the Laval nozzle.

Flow Evaluation in the Experimental Chamber for Supersonic Flow in Low Pressures

2018 ◽  
Vol 87 (1) ◽  
pp. 397-403
Author(s):  
Pavla Hlavatá ◽  
Jiří Maxa ◽  
Petr Vyroubal
Keyword(s):  
Supersonic Flow ◽  
Experimental Chamber ◽  
Low Pressures

Mathematical and Physical Analysis of the Effect of Conical and Detached Shock Waves at the Tip of a Static Probe in an Experimental Chamber

2021 ◽  
Vol 105 (1) ◽  
pp. 627-635
Author(s):  
Pavla Šabacká ◽  
Jiří Maxa ◽  
Anna Maxová
Keyword(s):  
Supersonic Flow ◽  
Static Pressure ◽  
Experimental Chamber ◽  
Physical Analysis ◽  
Pressure Measurements ◽  
Scientific Instruments ◽  
Electronic Technology ◽  
Vacuum Chambers ◽  
University Of Technology ◽  
Flow Through

As part of the research in the field of pumping vacuum chambers in the Environmental Electron Microscope, research on supersonic flow through apertures is being carried out at the Department of Electrical and Electronic Technology of the Brno University of Technology in cooperation with the Institute of Scientific Instruments of the CAS. This paper deals with the influence of the shape of the static probe cone design for static pressure measurements in the supersonic flow regime in the Experimental Chamber. The cone of the probe has an effect on the shape of the shock wave, which significantly influences the detected static pressure value.

Simulation of the Effect of Process Parameters on Particle Velocity in Cold Spray Using Laval Nozzle with Nine Holes

2011 ◽  
Vol 314-316 ◽  
pp. 78-81
Author(s):  
Chuan Shao Liu ◽  
Yao Hui Jin ◽  
Jian Xin Zheng
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Supersonic Flow ◽  
Flow Field ◽  
Particle Velocity ◽  
Laval Nozzle ◽  
Particle Diameter ◽  
Standoff Distance ◽  
Single Hole ◽  
Dynamics Method

Simulations of the supersonic flow field inside and outside of the Laval nozzle with single hole and nine holes were carried out based on the computational fluid dynamics method. The effects of different standoff distance and particle diameter on impact velocity of Cu particle spraying from single hole and nine holes were investigated firstly. The results show that the particle velocity obtained with the nine holes nozzle is higher than that of the single hole nozzle under the same standoff distance, and the smaller the standoff distance, the higher the particle velocity may be obtained with the nine holes, and the higher particle velocity may be obtained with smaller particle diameter for particles with diameters of 1 ~ 15 μm. Furthermore the effects of different spraying pressure and temperature on particle velocity of Cu particle spraying from the nine holes nozzle were also studied. And the simulations indicate that the higher the spraying pressure and temperature may make the particle spraying with greater velocity.

Mathematical-Physical Analysis of Drag Force of a .223 REM Caliber Projectile

2021 ◽  
Vol 105 (1) ◽  
pp. 637-645
Author(s):  
Pavla Šabacká ◽  
Jiří Maxa ◽  
Filip Maxa
Keyword(s):  
Shock Wave ◽  
Electron Microscope ◽  
Supersonic Flow ◽  
Drag Force ◽  
Physical Analysis ◽  
Vacuum Chambers ◽  
Aerodynamic Shape

This article deals with the mathematical and physical analysis of the drag force affecting a .223 REM projectile as a basis for further modification of the aerodynamic shape of the projectile by changing the perpendicular shock wave at the projectile tip into a conical one. For the analyses, the Department’s experience from the analysis of the supersonic flow generated during the pumping of the vacuum chambers of the electron microscope was used.

scholarly journals Micropillar Arrays for High Sensitivity Sensors

2014 ◽  
Vol 1685 ◽  
Author(s):  
Youngwoo Kim ◽  
Nakhiah Goulbourne
Keyword(s):  
Sensor Array ◽  
Pressure Sensors ◽  
High Sensitivity ◽  
Tactile Sensing ◽  
Preliminary Results ◽  
Aspect Ratios ◽  
Pixel Array ◽  
Low Pressures ◽  
Deformation Modes ◽  
Type Pressure

ABSTRACTIn this paper, we report on a new micropillar sensor array that is stretchable, flexible, and has high sensitivity in the tactile sensing regime (<10 kPa). The sensor array is capable of detecting deformation modes other than pressure such as shear and planar extension. The capacitance-type sensor is fabricated using soft nanolithography whereby the micropillars are individually electroded using a sputtering technique. Buckled gold electrodes are used in this study to enable large sensor stretches up to 55%. Three micropillar aspect ratios were considered in this work (1:1, 1:2, 1:3). Here we present the highest reported sensitivity [0.8 kPa-1] of a capacitance type flexible/stretchable sensor. Our results show that this sensor is also able to detect very low pressures down to 5.4 Pa, which is in the range of ultra-low detection pressures recently reported. Finally, the microstructured sensor array naturally lends itself to the development of pixel-type pressure sensors. We present preliminary results for a 25 pixel array.

Laminar boundary-layer reattachment in supersonic flow

1979 ◽  
Vol 90 (2) ◽  
pp. 289-303 ◽  
Author(s):  
P. G. Daniels
Keyword(s):  
Boundary Layer ◽  
Supersonic Flow ◽  
Bluff Body ◽  
Fundamental Problem ◽  
Reverse Flow ◽  
Correct Choice ◽  
Flow Profile ◽  
Local Flow ◽  
Boundary Layer Equations ◽  
Lower Deck

A rational theory is developed to describe the reattachment of a laminar shear layer in supersonic flow. In the neighbourhood of reattachment the flow develops a threetiered or ‘triple-deck’ structure analogous to that which occurs at a point of separation (Stewartson & Williams 1969) and, as in the separation problem, the local flow pattern may be found independently of the flow in the surrounding regions. The fundamental problem of the reattachment triple deck reduces to the solution of the incompressible boundary-layer equations in the lower deck, which is of streamwise and lateral dimensions O(R−⅜) and O(R−⅝), where R [Gt ] 1 is a representative Reynolds number for the flow. Pressure variations in this region are O(R−¼). Asymptotic solutions in terms of x, the scaled streamwise lower-deck variable, are derived to confirm the transition from a reverse flow profile at x = 0+, through reattachment, to a forward flow as x → ∞, the attainment of the required asymptotic form downstream (as x → ∞) being shown to depend crucially upon the correct choice of the finite part of the pressure in the lower deck at x = 0+. The lower-deck solution is singular at x = 0+ and assumes a complicated multi-structured form which is shown to match upstream with the solution in a largely inviscid region of dimension O(R−½) where the pressure is O(1) and the major part of the flow reversal takes place. Solutions are presented for reattachment at a wall and for symmetric reattachment behind a wedge or bluff body. In the former case the results also explain the apparent ignorance of upstream conditions in the expansive triple-deck solution formulated by Stewartson (1970) in the context of supersonic flow around a convex corner.

scholarly journals Sensitive capacitive pressure sensors based on graphene membrane arrays

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Makars Šiškins ◽  
Martin Lee ◽  
Dominique Wehenkel ◽  
Richard van Rijn ◽  
Tijmen W. de Jong ◽  
...  
Keyword(s):  
Low Cost ◽  
Pressure Sensors ◽  
Small Diameter ◽  
Circuit Board ◽  
High Temperature Annealing ◽  
Layer Graphene ◽  
Graphene Membrane ◽  
Highly Sensitive ◽  
High Flexibility ◽  
Graphene Membranes

AbstractThe high flexibility, impermeability and strength of graphene membranes are key properties that can enable the next generation of nanomechanical sensors. However, for capacitive pressure sensors, the sensitivity offered by a single suspended graphene membrane is too small to compete with commercial sensors. Here, we realize highly sensitive capacitive pressure sensors consisting of arrays of nearly ten thousand small, freestanding double-layer graphene membranes. We fabricate large arrays of small-diameter membranes using a procedure that maintains the superior material and mechanical properties of graphene, even after high-temperature annealing. These sensors are readout using a low-cost battery-powered circuit board, with a responsivity of up to $$47.8$$ 47.8  aF Pa−1 mm−2, thereby outperforming the commercial sensors.

Numerical simulation of highly-swirling supersonic flow inside a Laval nozzle

2008 ◽  
Vol 8 (7/8) ◽  
pp. 536 ◽  
Author(s):  
Zhongliang Liu ◽  
Juntao Ding ◽  
Wenming Jiang ◽  
Jian Zhang ◽  
Yongxun Feng
Keyword(s):  
Numerical Simulation ◽  
Supersonic Flow ◽  
Laval Nozzle

scholarly journals Nonlinear Position Control with Nonlinear Coordinate Transformation Using Only Position Measurement for Single-Rod Electro-Hydrostatic Actuator

Mathematics ◽  
2020 ◽  
Vol 8 (8) ◽  
pp. 1273
Author(s):  
Wonhee Kim ◽  
Daehee Won
Keyword(s):  
Coordinate Transformation ◽  
Position Control ◽  
Internal State ◽  
Pressure Sensors ◽  
Nonlinear Observer ◽  
Position Tracking ◽  
State Variables ◽  
Position Measurement ◽  
Full State ◽  
Position Controller

In existing methods, full-state feedback is required for the position tracking of single-rod Electro Hydrostatic Actuators (EHAs). Measuring a full state is not always possible because of cost and space limitations. Furthermore, measurement noise from pressure sensors may degrade the control performance. We propose an observer-based nonlinear position control with nonlinear coordinate transformation while only using position measurement to improve the position tracking of single-rod EHAs. The proposed method comprises a position controller and an observer. We propose a nonlinear coordinate transform for the controller design. The desired force is designed for the position tracking and boundedness of the internal state. The position controller is designed to track the desired state variables for the EHAs. Meanwhile, a nonlinear observer is proposed in order to estimate a full state using only the position measurement. The stability of the closed-loop system is investigated via an input-to-state stability property. The performance of the proposed method is validated via both simulations and experiments.

Analysis of the Effect of Reflected Shock Waves in the Experimental Chamber

2021 ◽  
Vol 105 (1) ◽  
pp. 589-599
Author(s):  
Jiří Maxa ◽  
Pavla Šabacká ◽  
Robert Bayer
Keyword(s):  
Electron Microscope ◽  
Supersonic Flow ◽  
Shock Waves ◽  
Vacuum Chamber ◽  
Experimental Chamber ◽  
Scientific Instruments ◽  
Electronic Technology ◽  
Reflected Shock ◽  
University Of Technology ◽  
Flow Through

As part of the research in the field of vacuum chamber pumping in the Environmental Electron Microscope, research on supersonic flow through apertures is being carried out at the Department of Electrical and Electronic Technology of Brno University of Technology in cooperation with the Institute of Scientific Instruments of the CAS. This paper deals with the influence of reflected shock waves on the resulting flow in the pumped part of the Experimental Chamber.

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