An Assessment of Homogeneous Mixture Method Cavitation Models in Predicting Cavitation in Nozzle Flow

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Dorien O. Villafranco ◽  
Ankush Gupta ◽  
Emily M. Ryan ◽  
R. Glynn Holt ◽  
Sheryl M. Grace
Keyword(s):  
Formation Rate ◽  
Computational Prediction ◽  
Quantitative Information ◽  
Homogeneous Mixture ◽  
Nozzle Flow ◽  
Validation Data ◽  
Cavitation Inception ◽  
Input Parameters ◽  
Cavitation Detection ◽  
Vapor Formation

Abstract The homogeneous mixture method (HMM) is a popular class of models used in the computational prediction of cavitation. Several cavitation models have been developed for use with HMM to govern the development and destruction of vapor in a fluid system. Two models credited to Kunz and Schnerr–Sauer are studied in this paper. The goal of this work is to provide an assessment of the two cavitation submodels in their ability to predict cavitation in nozzle flow. Validation data were obtained via experiments which employ both passive cavitation detection, (PCD) via acoustic sensing and optical cavitation detection (OCD) via camera imaging. The experiments provide quantitative information on cavitation inception and qualitative information on the vapor in the nozzle. The results show that initial vapor formation is not predicted precisely but within reason. A sensitivity analysis of the models to input parameters shows that the Schnerr–Sauer method does not depend upon the estimation of nuclei size and number density. Small changes in the vapor formation rate but not the total vapor volume can be seen when weighting parameters are modified. In contrast, changes to the input parameters for the Kunz model greatly change the final total vapor volume prediction. The assessment also highlights the influence of vapor convection within the method. Finally, the analysis shows that if the fluid and nozzle walls do not support nuclei larger than 40 μm, the methods would still predict cavitation when indeed there would be none in practice.

Assessment of Cavitation Models in the Prediction of Cavitation in Nozzle Flow

2018 ◽  
Author(s):  
Dorien O. Villafranco ◽  
Huy K. Do ◽  
Sheryl M. Grace ◽  
Emily M. Ryan ◽  
R. Glynn Holt
Keyword(s):  
Volume Fraction ◽  
Quantitative Information ◽  
Nozzle Geometry ◽  
Fuel Injector ◽  
Validation Data ◽  
Cavitation Inception ◽  
Tuning Parameters ◽  
Acoustic Techniques ◽  
Models Validation ◽  
Cavitation Detection

Cavitation inside fuel injector nozzles has been linked not only to erosion of the solid surface, but also to improved spray atomization. To quantify the effects of the resulting occurrences, the prediction of cavitation through computational modeling is vital. Homogeneous mixture methods (HMM) make use of a variety of cavitation sub-models such as those developed by Kunz, Merkle, and Schnerr-Sauer, to describe the phase change from liquid to vapor and vice-versa in the fluid system. The aforementioned cavitation models all have several free-tuning parameters which have been shown to affect the resulting prediction for vapor volume fraction. The goal of the current work is to provide an assessment of the Kunz and Schnerr-Sauer cavitation models. Validation data have been obtained via experiments which employ both acoustic techniques (passive cavitation detection, or PCD) and optical techniques (optical cavitation detection, or OCD). The experiments provide quantitative information on cavitation inception and qualitative information as to overall vapor fraction as a function of flow rate, and nozzle geometry. It is shown that inception is fairly well captured but the amount of vapor predicted is far too low. A sensitivity analysis on the tuning parameters in the cavitation models leads to some explainable trends, however, several parameter sweeps results in outlier predictions. Recommendations for their usability and suggestions for improvement are presented.

scholarly journals Detection of Inception Cavitation in Centrifugal Pump by Fluid-Borne Noise Diagnostic

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Liang Dong ◽  
Yuqi Zhao ◽  
Cui Dai
Keyword(s):  
Centrifugal Pump ◽  
Detection Threshold ◽  
High Sensitivity ◽  
Pressure Level ◽  
Experimental Methodology ◽  
Detection Methods ◽  
Cavitation Inception ◽  
Cavitation Performance ◽  
Pattern Distribution ◽  
Cavitation Detection

This paper presents an experimental methodology that is capable of sensitively detecting the cavitation inception in a centrifugal pump. Firstly, with a centrifugal pump of ns=117 as research object, the cavitation performance, the bubble pattern distribution at impeller inlet, and the vibration and noise were synchronously measured at different flow conditions each with several cavitation coefficients. The change laws of total level of vibration and noise signals throughout the cavitation process were emphatically investigated. After comparing the sensitivity and reliability of different detection methods, the method based on overall sound pressure level of liquid-borne noise is found to present high sensitivity to cavitation. Secondly, by comparing the affected 1/3 octave spectrum by changing flow and cavitation coefficients, the highly sensitive frequency band to cavitation was obtained. Then, a new inception cavitation detection method was proposed based on Pauta principle. Finally, the method was verified through an ultra-low-specific speed pump (ns=25). The results show that the total pressure level of liquid-borne noise increases firstly and then decreases with the development of cavitation. The broadband SPL of liquid-borne noise between 2000 and 3000 Hz can be used to detect the inception cavitation, and the cavitation detection threshold is determined as 1.0%.

Investigation of Nozzle Flow and Cavitation Characteristics in a Diesel Injector

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
S. Som ◽  
S. K. Aggarwal ◽  
E. M. El-Hannouny ◽  
D. E. Longman
Keyword(s):  
Nozzle Exit ◽  
Critical Role ◽  
Injection Pressure ◽  
Nozzle Flow ◽  
Two Phase ◽  
Cavitation Inception ◽  
Diesel Fuels ◽  
Needle Position ◽  
Primary Breakup ◽  
Cavitation Behavior

Cavitation and turbulence inside a diesel injector play a critical role in primary spray breakup and development processes. The study of cavitation in realistic injectors is challenging, both theoretically and experimentally, since the associated two-phase flow field is turbulent and highly complex, characterized by large pressure gradients and small orifice geometries. We report herein a computational investigation of the internal nozzle flow and cavitation characteristics in a diesel injector. A mixture based model in FLUENT V6.2 software is employed for simulations. In addition, a new criterion for cavitation inception based on the total stress is implemented, and its effectiveness in predicting cavitation is evaluated. Results indicate that under realistic diesel engine conditions, cavitation patterns inside the orifice are influenced by the new cavitation criterion. Simulations are validated using the available two-phase nozzle flow data and the rate of injection measurements at various injection pressures (800–1600 bar) from the present study. The computational model is then used to characterize the effects of important injector parameters on the internal nozzle flow and cavitation behavior, as well as on flow properties at the nozzle exit. The parameters include injection pressure, needle lift position, and fuel type. The propensity of cavitation for different on-fleet diesel fuels is compared with that for n-dodecane, a diesel fuel surrogate. Results indicate that the cavitation characteristics of n-dodecane are significantly different from those of the other three fuels investigated. The effect of needle movement on cavitation is investigated by performing simulations at different needle lift positions. Cavitation patterns are seen to shift dramatically as the needle lift position is changed during an injection event. The region of significant cavitation shifts from top of the orifice to bottom of the orifice as the needle position is changed from fully open (0.275 mm) to nearly closed (0.1 mm), and this behavior can be attributed to the effect of needle position on flow patterns upstream of the orifice. The results demonstrate the capability of the cavitation model to predict cavitating nozzle flows in realistic diesel injectors and provide boundary conditions, in terms of vapor fraction, velocity, and turbulence parameters at the nozzle exit, which can be coupled with the primary breakup simulation.

CFD Methods for Shear Driven Liquid Wall Films

2010 ◽  
Author(s):  
Amir A. Hashmi ◽  
Klaus Dullenkopf ◽  
Rainer Koch ◽  
Hans-Jo¨rg Bauer
Keyword(s):  
Multiphase Flow ◽  
Practical Importance ◽  
Quantitative Information ◽  
Gas Production ◽  
Vof Method ◽  
Original Form ◽  
Test Case ◽  
Validation Data ◽  
Liquid Wall ◽  
Interface Treatment

Shear driven liquid wall films or physically similar two phase flow phenomena can be found in a number of different industrial and engineering applications. Gear boxes, bearing chambers or combustors in aero engines, heat exchanger ducts, oil and gas production and transport in petrochemical industry are just a few examples where this phenomenon is present and has been studied for decades. The most common approach of modeling shear driven film flows consist of empirical correlations derived from simple experiments. This approach is reasonable but highly case dependent. The problem lies in the difficulty of achieving experimental data for cases of practical importance. For a more global approach in this respect, CFD can be a useful tool. Therefore the study presented in this paper is dedicated to explore the potential of modern CFD methods. All available multiphase flow models are analyzed for their applicability for subcritical shear driven wall films (no mass transfer, no droplet shedding/deposition from/to film). VOF is suggested to be the only available multiphase flow model applicable to shear driven flows. However, further investigations have revealed that VOF method in its original form is not suitable for the flow conditions leading to high interaction between the phases i.e. where the motion of slow moving heavier phase is dictated by the fast moving lighter phase. This shortcoming in the VOF method is explained by means of a false momentum transfer between the phases. The focus then turns to find the improvement possibilities in the VOF method. Two approaches can be found in literature addressing the improvement possibilities in VOF method. The approach of physically justified modification of the turbulence quantities at the gas-liquid interface is adopted in this paper and is referred to as interface treatment. The approach is applied to a simple test case where the liquid phase acts as a wall. The results achieved for this test case are compared to the validation data where remarkable improvements are observed when compared to the VOF method without interface treatment. The interface treatment is then applied to a case of more practical importance where improvements are clearly evident again. Due to the lack of quantitative information on the interfacial waves, outlet boundary conditions cannot be well defined at this point. Therefore the later case is only seen as a motivation for further investigation of this approach.

Cavitation detection in a nozzle flow

2017 ◽  
Vol 141 (5) ◽  
pp. 3738-3739
Author(s):  
Huy K. Do ◽  
Purity Dele-Oni ◽  
Tony Tang ◽  
Daniel Poe ◽  
James Bird ◽  
...  
Keyword(s):  
Nozzle Flow ◽  
Cavitation Detection

scholarly journals Experimental performance analysis of a multiple-source and multiple-use heat pump system: a predictive ANN model of sky-source heat pump

2019 ◽  
Vol 111 ◽  
pp. 05018
Author(s):  
Ke Wen ◽  
Ryozo Ooka ◽  
Toshiyuki Hino ◽  
Mingzhe Liu ◽  
Doyun Lee ◽  
...  
Keyword(s):  
Heat Pump ◽  
Learning Curves ◽  
Training Data ◽  
Coefficient Of Performance ◽  
Ann Model ◽  
Validation Data ◽  
Data Set ◽  
Pump System ◽  
Heat Pump System ◽  
Input Parameters

In this study, an artificial neural network (ANN) was used to model the thermal performance of a novel direct-expansion solar-assisted sky-source heat pump (SSHP) during winter. The input parameters of the ANN take into account the weather conditions, water loop characteristics, and the compressor characteristics of the SSHP. The following four output parameters were adopted to evaluate the SSHP performance: the outlet water temperature of the water loop, electricity consumption, heat production, and the coefficient of performance. To increase the accuracy of the ANN and simultaneously investigate the effects of each of the input parameters on the performance of the SSHP, the combination of input parameters for the validation data set was varied in multiple case studies. Additionally, learning curves were introduced to clarify the relationship between the training data size and the generalization performance of the ANN. Finally, the ANNs with the best performance were selected and evaluated based on the test data set by using metrics such as the root mean square error. The reported results demonstrated that the ANN model has comparatively high SSHP winter performance prediction accuracy.

Numerical and Experimental Investigations of Cavitating Flow in a Vertical Multi-Hole Injector Nozzle

2010 ◽  
Author(s):  
Zhixia He ◽  
Jing Bai ◽  
Qian Wang ◽  
Qingmu Mu ◽  
Yunlong Huang
Keyword(s):  
Numerical Simulation ◽  
Numerical Models ◽  
Three Dimensional ◽  
Injection Pressure ◽  
Cavitating Flow ◽  
Critical Conditions ◽  
Experimental Investigations ◽  
Nozzle Flow ◽  
Cavitation Inception ◽  
Injector Nozzle

The presence of cavitation and turbulence in a diesel injector nozzle has significant effect on the subsequent spray characteristics. However, the mechanism of the cavitating flow and its effect on the subsequent spray is unclear because of the complexities of the nozzle flow, such as the cavitation phenomena and turbulence. A flow visualization experiment system with a transparent scaled-up vertical multi-hole injector nozzle tip was setup for getting the experimental data to make a comparison to validate the calculated results from the three dimensional numerical simulation of cavitating flow in the nozzle with mixture multi-phase cavitating flow model and good qualitative agreement was seen between the two sets of data. The critical conditions for cavitation inception were derived as well as the relationship between the discharge coefficient and non-dimensional cavitation parameter. After wards, the testified numerical models were used to analyze the effects of injection pressure, back pressure, cavitation parameter, Reynolds number, injector needle lift and needle eccentricity on the cavitating flow inside the nozzle. Combined with visual experimental results, numerical simulation results can clearly reveal the three-dimensional nature of the nozzle flow and the location and shape of the cavitation induced vapor distribution, which can help understand the nozzle flow better and eventually put forward the optimization ideas of diesel injectors.

Runout modeling based debris flow risk assessment: a case study from Garhwal Himalaya, India

2020 ◽  
Author(s):  
Rajesh Kumar Dash ◽  
Debi Prasanna Kanungo
Keyword(s):  
Risk Assessment ◽  
Debris Flow ◽  
Debris Flows ◽  
Back Analysis ◽  
Source Area ◽  
Quantitative Information ◽  
Source Zone ◽  
Garhwal Himalayas ◽  
Model Input ◽  
Input Parameters

<p>Debris flows are one of the most frequently occurring and destructive hazards in Indian Himalayas which are often initiated by rainfall.  To minimize the losses due to the destructive power of the debris flows, demarcation of debris flow risk zones is an effective practice for risk reduction. In the present study, site specific debris flow risk assessment has been carried out based upon runout behaviour modeling. Tangni debris flow is an active debris flow in the Chamoli district of Garhwal Himalayas, India which is responsible for disrupting the traffic by blocking the road for days. This debris flow is repetitive in nature and occurs many a times every year in the monsoon during the months between June to September. The Tangni debris flow is categorized as a hill slope debris flow and the failure is considered as a block failure. Runout modeling of Tangni debris flow has been carried out using a Voellmy approach based continuum model. Quantitative information on debris flow intensity parameters such as flow velocity, height and pressure was obtained from the numerical simulation. The calibration of model input parameters was done by back analysis of an event from a particular source area that took place in 2013. Depending upon the amount of materials present in different source areas in the entire source zone and using the calibrated model input parameters, several simulations were performed to assess the flow behaviour of at different possible scenarios. Thus, Tangni debris flow risk assessment has been carried out based on its runout effect modeling. This study revealed that there may be a possibility of damming of river as well as blocking of the National Highway which are located at the downstream of the debris flow.</p><p>Key words:  Debris flow, Risk assessment, Runout modeling, Garhwal Himalayas, Voellmy model</p>

Some Results of the Spectroscopic Study of Four Close Binary Systems of Early Spectral Types

1965 ◽  
Vol 5 ◽  
pp. 120-130
Author(s):  
T. S. Galkina
Keyword(s):  
Spectroscopic Study ◽  
Spectral Type ◽  
Spectroscopic Investigation ◽  
Binary Systems ◽  
Quantitative Information ◽  
Close Binary ◽  
Physical Parameters ◽  
Absorption And Emission ◽  
Close Binary Systems ◽  
Quantitative Estimates

It is necessary to have quantitative estimates of the intensity of lines (both absorption and emission) to obtain the physical parameters of the atmosphere of components.Some years ago at the Crimean observatory we began the spectroscopic investigation of close binary systems of the early spectral type with components WR, Of, O, B to try and obtain more quantitative information from the study of the spectra of the components.

The direct determination of magnetic domain wall profiles using a split detector STEM

1978 ◽  
Vol 36 (1) ◽  
pp. 466-467
Author(s):  
J.N. Chapman ◽  
P.E. Batson ◽  
E.M. Waddell ◽  
R.P. Ferrier
Keyword(s):  
Electron Microscope ◽  
Domain Wall ◽  
Transmission Electron Microscope ◽  
Domain Walls ◽  
Photographic Plate ◽  
Magnetic Domain ◽  
Direct Determination ◽  
Quantitative Information ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron

By far the most commonly used mode of Lorentz microscopy in the examination of ferromagnetic thin films is the Fresnel or defocus mode. Use of this mode in the conventional transmission electron microscope (CTEM) is straightforward and immediately reveals the existence of all domain walls present. However, if such quantitative information as the domain wall profile is required, the technique suffers from several disadvantages. These include the inability to directly observe fine image detail on the viewing screen because of the stringent illumination coherence requirements, the difficulty of accurately translating part of a photographic plate into quantitative electron intensity data, and, perhaps most severe, the difficulty of interpreting this data. One solution to the first-named problem is to use a CTEM equipped with a field emission gun (FEG) (Inoue, Harada and Yamamoto 1977) whilst a second is to use the equivalent mode of image formation in a scanning transmission electron microscope (STEM) (Chapman, Batson, Waddell, Ferrier and Craven 1977), a technique which largely overcomes the second-named problem as well.

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