A Comparison Between Numerical and Experimental High Reynolds Number Supersonic Jets Generated by Millimeter Scale Converging-Diverging Nozzles

Abstract In thermal spray applications, such as cold spray, an inert gas jet (typically helium or nitrogen) is used to accelerate micron scale particles to supersonic velocities. The complex gas dynamics of these supersonic jets are critical to understand via computational methods for the control of the spray. This work compares supersonic jet waveforms visualized by schlieren imaging with those predicted by computational fluid dynamics (CFD) simulations. A supersonic nitrogen jet is produced by a millimeter scale converging-diverging nozzle with inlet pressures as high as 50 bars. The jet Reynolds numbers based on the nozzle exit diameter and stagnation gas properties range between 60,000 to 325,000. A schlieren visualization setup has been built which shows the first spatial derivative of densities within the flow field. The strong density gradients across the oblique shock waves in the jets allow for clear photographs of the flow pattern of the jets using this schlieren visualization setup. Comparisons between the experiments and the CFD results act as a validation technique for the accuracy of the simulations in terms of the positions and orientations of the oblique shock waves. Through this study, the nozzle internal surface roughness is determined to be a critical parameter in millimeter scale nozzles for the development of the boundary layer. The CFD surface roughness parameters inside the nozzle are incremented until the geometry of the oblique shock waves matches the schlieren images. This work validates the simulation techniques which will be used for future jet simulations, in which shock wave locations and orientations are important, such as jet impingement on a flat plate and particle-shock interactions.

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The Occurrence of Stagnation Bubbles in Supersonic Jet Impingement Flows

Aeronautical Quarterly ◽

10.1017/s0001925900007678 ◽

1976 ◽

Vol 27 (3) ◽

pp. 169-185 ◽

Cited By ~ 69

Author(s):

G T Kalghatgi ◽

B L Hunt

Keyword(s):

Shock Waves ◽

Supersonic Jet ◽

Weak Shock ◽

Jet Impingement ◽

Flat Plates ◽

Number Range ◽

Shock Interactions ◽

Free Jet ◽

Nozzle Contour ◽

Inherent Part

SummaryThis paper reports an experimental investigation into the stagnation bubbles found in the shock layers of some supersonic jets impinging on perpendicular flat plates at small nozzle-to-plate distances. The experiments used twelve contoured nozzles within the Mach number range 1.42 to 2.83. Surface pressures were measured on the plate and free-jet pitot pressure distributions were obtained at the level of the centre of the plate shock. Schlieren pictures were taken of both impinging and free jets. It was found that the bubbles result from the interaction of the plate shock with very weak shock waves which are produced in the jet either by small imperfections in the nozzle wall or by slight inaccuracies in the design or production of the nozzle contour. The bubbles can be eliminated by suitable improvements to the nozzle. Other anomalous flows produced by shock interactions are described and explanations offered. It is shown that the bubbles sometimes encountered at close plate spacings with conical nozzles are also due to shock waves. However, for wide-angled nozzles, internal shocks can be an inherent part of the flow from the nozzle and the bubbles which they produce are thus an inherent part of the impingement flow. From physical arguments concerning the main factors involved in producing a bubble, a parameter is constructed whose values are shown to be a good criterion for whether a bubble occurs or not.

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Study of a Novel Honeycomb Continuous Flocculator

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1033-1034.435 ◽

2014 ◽

Vol 1033-1034 ◽

pp. 435-438

Author(s):

Ming Dong ◽

Qiong Fang Shao

Keyword(s):

Surface Roughness ◽

Grain Size ◽

Flow Resistance ◽

Separation Efficiency ◽

Sewage Treatment ◽

Internal Surface ◽

Industrial Fermentation ◽

Fermentation Liquid ◽

Solid Liquid ◽

Solid Liquid Separation

The continuous flocculator described in this article refers to a kind of continuous flocculation device designed to flocculate fermentation liquid. The honeycomb continuous flocculator is composed of a vessel and built-in trapezoid subassemblies, which divide the space within the vessel into multiple honeycomb channels. The length ratio between the longest diagonal of the regular hexagon and the axial length of the channel is within the range 0.01–0.04; and the internal surface roughness (Ra) of the channels should be 0 < Ra ≤ 0.2 μm. In contrast to current flocculator designs, the channels of the honeycomb continuous flocculator could control the floc grain size, grain fineness distribution in the fermentation liquid and flocculating time and decrease the flow resistance of the flocculating fermentation liquid and increase handling capacity. These capabilities improve solid-liquid separation efficiency for fermentation liquids. The flocculator could be used either for purification of industrial fermentation liquids or sewage treatment.

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Estimation of Internal Surface Roughness of Additively Manufactured Components Under Complex Conditions Using Artificial Intelligence and Measurements of Ultrasonic Backscatter

10.1115/qnde2021-75106 ◽

2021 ◽

Author(s):

Mohamed Subair Syed Akbar Ali ◽

Mato Pavlovic ◽

Prabhu Rajagopal

Keyword(s):

Artificial Intelligence ◽

Surface Roughness ◽

Internal Surface ◽

Side Surface ◽

Ultrasonic Waves ◽

Model Parameters ◽

Ultrasonic Measurements ◽

Neural Network Algorithm ◽

X Ray Computed ◽

Pulse Echo

Abstract Additive Manufacturing (AM) is increasingly being considered for fabrication of components with complex geometries in various industries such as aerospace and healthcare. Control of surface roughness of components is thus a crucial aspect for more widespread adoption of AM techniques. However, estimating the internal (or ‘far-side’) surface roughness of components is a challenge, and often requires sophisticated techniques such as X-ray computed tomography, which are difficult to implement online. Although ultrasound could potentially offer a solution, grain noise and inspection surface conditions complicate the process. This paper studies the feasibility of using Artificial Intelligence (AI) in conjunction with ultrasonic measurements for rapid estimation of internal surface roughness in AM components, using numerical simulations. In the first models reported here, a pulse-echo configuration is assumed, whereby a specimen sample with rough surfaces is insonified with bulk ultrasonic waves and the backscatter is used to generate A-scans. Simulations are carried out for various combinations of the model parameters, yielding a large number of such A-scans. A neural network algorithm is then created and trained on a subset of the datasets so generated using simulations, and later used to predict the roughness from the rest. The results demonstrate the immense potential of this approach in inspection automation for rapid roughness assessments in AM components, based on ultrasonic measurements.

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Microramp Flow Control for Oblique Shock Interactions: Comparisons of Computational and Experimental Data

5th Flow Control Conference ◽

10.2514/6.2010-4973 ◽

2010 ◽

Cited By ~ 1

Author(s):

Stefanie Hirt ◽

David Reich ◽

Michael O'Connor

Keyword(s):

Experimental Data ◽

Flow Control ◽

Oblique Shock ◽

Shock Interactions

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High Frequency Acoustic Signal Analysis for Internal Surface Pipe Roughness Classification

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.83.249 ◽

2011 ◽

Vol 83 ◽

pp. 249-254

Author(s):

Z. M. Hafizi ◽

Che Ku Eddy Nizwan ◽

M.F.A. Reza ◽

M.A.A. Johari

Keyword(s):

Surface Roughness ◽

Acoustic Emission ◽

Control Valve ◽

Internal Surface ◽

Corrosion Monitoring ◽

Emission Analysis ◽

Pressure Water ◽

Pipe Roughness ◽

The Time Domain ◽

Roughness Classification

This research highlights a method of acoustic emission analysis to distinguish the internal surface roughness of pipe. Internal roughness of pipe indicates the level of corrosion occurring, where normally it is difficult to be monitored online. Acoustic Emission (AE) technique can be used as an alternative solution for corrosion monitoring in pipes, especially for complex pipelines that are difficult to achieve by other monitoring devices. This study used a hydraulic bench to provide fluid flow at two different pressures in pipes with different internal surface roughness (rough and smooth). The main source of acoustic emission was from activity in the control valve, coupled with high pressure water flow friction on the surface of the pipe. The signal from these sources was detected by using the AED-2000V instrument and assisted by the Acoustic Emission Detector (AED) software. The time domain parameter; root mean square, RMS amplitude were processed and compared at different pressures for each type of internal pipe roughness at ten different locations. It was observed that a unitless Bangi number, AB, derived from RMS values, can be used for discriminating different level of internal surface roughness. Internal surface pipe can still be considered as smooth if AB value is above 1.0.

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Surface Roughness Effects on Circular Cylinders at High Reynolds Numbers

5th International Symposium on Fluid Structure International, Aeroeslasticity, and Flow Induced Vibration and Noise ◽

10.1115/imece2002-32160 ◽

2002 ◽

Author(s):

M. Eaddy ◽

W. H. Melbourne ◽

J. Sheridan

Keyword(s):

Surface Roughness ◽

Reynolds Numbers ◽

Circular Cylinders ◽

Flow Induced Vibration ◽

Roughness Effects ◽

Vortex Induced Vibration ◽

Smooth Cylinder ◽

Lift Forces ◽

High Reynolds ◽

Effect Of Surface

The problem of flow-induced vibration has been studied extensively. However, much of this research has focused on the smooth cylinder to gain an understanding of the mechanisms that cause vortex-induced vibration. In this paper results of an investigation of the effect of surface roughness on the cross-wind forces are presented. Measurements of the sectional RMS fluctuating lift forces and the axial correlation of the pressures for Reynolds numbers from 1 × 105 to 1.4 × 106 are given. It was found that surface roughness significantly increased the axial correlation of the pressures to similar values found at high subcritical Reynolds numbers. There was little effect of the surface roughness on the sectional lift forces. The improved correlation of the vortex shedding means rough cylinders will be subject to larger cross-wind forces and an increased possibility of vortex-induced vibration compared to smooth cylinders.

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