scholarly journals Computational Test Design for High-Speed Liquid Impact and Dispersal

2011 ◽  
Author(s):  
Alexander L. Brown ◽  
Kurt E. Metzinger
Keyword(s):  
High Speed ◽  
Water Channel ◽  
Computational Method ◽  
Computational Fluid Mechanics ◽  
Reacting Flow ◽  
Validation Data ◽  
Sled Test ◽  
The Impact ◽  
Scale Data ◽  
Limited Scope

Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that must be resolved for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been developed for modeling the impact and subsequent liquid spread. This involves coupling a structural dynamics code to a turbulent computational fluid mechanics reacting flow code. Because the environment intended to be simulated with this capability is difficult to instrument and costly to test, the existing validation data are of limited scope, relevance, and quality. A rocket sled test is being performed where a scoop moving through a water channel is being used to brake a pusher sled. We plan to instrument this test to provide appropriate scale data for validating the new modeling capability. The intent is to get high fidelity data on the break-up and evaporation of the water that is ejected from the channel as the sled is braking. These two elements are critical to fireball formation for this type of event involving fuel in the place of water. We demonstrate our capability in this paper by describing the pre-test predictions which are used to locate instrumentation for the actual test. We also present a sensitivity analysis to understand the implications of length scale assumptions on the prediction results.

Fluid Spread Model Validation for Emerging Liquid Tank Impact Predictive Methods

2010 ◽  
Author(s):  
Alexander L. Brown ◽  
Gregory J. Wagner
Keyword(s):  
Liquid Surface ◽  
Computational Method ◽  
Validation Data ◽  
Surface Deposition ◽  
Modeling Methods ◽  
Spread Model ◽  
Predictive Methods ◽  
Physical Representation ◽  
The Impact ◽  
Limited Scope

Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that are necessary to resolve for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been described for modeling the impact and subsequent liquid spread. Because the environment is difficult to instrument and costly to test, the existing validation data are of limited scope and quality. A comparatively well instrumented test involving a rocket propelled cylindrical tank of water was performed, the results of which are helpful to understand the adequacy of the modeling methods. Existing data include estimates of drop sizes at several locations, final liquid surface deposition mass integrated over surface area regions, and video evidence of liquid cloud spread distances. Comparisons are drawn between the experimental observations and the predicted results of the modeling methods to provide evidence regarding the accuracy of the methods.

scholarly journals Impact, Fire, and Fluid Spread Code Coupling for Complex Transportation Accident Environment Simulation

2012 ◽  
Vol 4 (2) ◽  
Author(s):  
Alexander L. Brown ◽  
Gregory J. Wagner ◽  
Kurt E. Metzinger
Keyword(s):  
Liquid Surface ◽  
Computational Method ◽  
Validation Data ◽  
Surface Deposition ◽  
Modeling Methods ◽  
Physical Representation ◽  
Environment Simulation ◽  
The Impact ◽  
Limited Scope ◽  
Existing Data

Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that are necessary to resolve for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been described for modeling the impact and subsequent liquid spread. Because the environment is difficult to instrument and costly to test, the existing validation data are of limited scope and quality. A comparatively well instrumented test involving a rocket propelled cylindrical tank of water was performed, the results of which are helpful to understand the adequacy of the modeling methods. Existing data include estimates of drop sizes at several locations, final liquid surface deposition mass integrated over surface area regions, and video evidence of liquid cloud spread distances. Comparisons are drawn between the experimental observations and the predicted results of the modeling methods to provide evidence regarding the accuracy of the methods, and to provide guidance on the application and use of these methods.

scholarly journals Impact of a Centrebody on the Unsteady Flow Dynamics of A Swirl Nozzle: Intermittency of PVC Oscillations

2021 ◽  
Author(s):  
Saarthak Gupta ◽  
Santosh Hemchandra ◽  
Masayasu Shimura ◽  
Santosh Shanbhogue ◽  
Ahmed Ghoniem
Keyword(s):  
Nozzle Exit ◽  
High Speed ◽  
Vortex Breakdown ◽  
Flow Dynamics ◽  
Reacting Flow ◽  
Exit Plane ◽  
Swirl Combustor ◽  
Time Resolved ◽  
Precessing Vortex Core ◽  
The Impact

Abstract The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic helical mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. The PVC can impact emissions and thermoacoustic stability characteristics of combustors in various ways, as several prior studies have shown. In this paper, we examine the impact of centrebody diameter (Dc) on the PVC in a non-reacting flow in a single nozzle swirl combustor. Time resolved high speed stereoscopic PIV (sPIV) measurements are performed for combinations of two swirl numbers, S = 0.67 and 1.17 and Dc = 9.5 mm, 4.73 mm and 0 (i.e. no centrebody). The bulk flow velocity at the nozzle exit plane is kept constant as Ub = 8 m/s for all cases (Re ∼ 20,000). The centrebody end face lies in the nozzle exit plane. A new modal decomposition technique based on wavelet filtering and proper orthogonal decomposition (POD) provides insight into flow dynamics in terms of global modes extracted from the data. The results show that without a centrebody, a coherent PVC is present in the flow as expected. The introduction of a centrebody makes the PVC oscillations intermittent. These results suggest two routes to intermittency as follows. For S = 0.67, the vortex breakdown bubble (VBB) and centrebody wake recirculation zone (CWRZ) regions are nominally distinct. Intermittent separation and merger due to turbulence result in PVC oscillations due to the de-stabilization of the hydrodynamic VBB precession mode of the flow. In the S = 1.17 case, the time averaged VBB position causes it to engulf the centrebody. In this case, the emergence of intermittent PVC oscillations is a result of the response of the flow to broadband stochastic forcing imposed on the time averaged vorticity field due to turbulence.

scholarly journals Impact of a Centrebody On the Unsteady Flow Dynamics of a Swirl Nozzle: Intermittency of PVC Oscillations

2021 ◽  
Author(s):  
Saarthak Gupta ◽  
Santosh Shanbhogue ◽  
Masayasu Shimura ◽  
Ahmed F. Ghoniem ◽  
Santosh Hemchandra
Keyword(s):  
High Speed ◽  
Vortex Breakdown ◽  
Flow Dynamics ◽  
Axial Position ◽  
Intermittent Flow ◽  
Reacting Flow ◽  
Hydrodynamic Mode ◽  
Time Resolved ◽  
Precessing Vortex Core ◽  
The Impact

Abstract The precessing vortex core (PVC) is a self-excited flow oscillation state occurring in swirl nozzles. This is caused by the presence of a marginally unstable hydrodynamic mode that induces precession of the vortex breakdown bubble (VBB) around the flow axis. We examine the impact of a centrebody on PVC dynamics in a non-reacting flow in a swirl nozzle combustor. Time resolved high speed stereoscopic PIV measurements are performed for two swirl numbers, S=0.67 and 1.17 and three centrebody diameters, 9.5mm, 4.73mm and 0 (i.e. no centrebody). The bulk flow velocity at the nozzle exit is kept constant as Ub=8m/s for all cases (Re~20,000). The data is analyzed using a new modal decomposition technique that combines the wavelet transform and proper orthogonal decomposition (WPOD). This gives insight into globally intermittent flow dynamics. A coherent PVC is present in the flow when there is no centrebody. Introducing a centrebody makes the PVC oscillations intermittent. The WPOD results show two qualitatively different intermittent behaviours at S=0.67 and 1.17. For S=0.67, the axial position of the VBB suggests that turbulence destabilizes the PVC mode by causing intermittent separation of the VBB and centrebody wake, resulting in PVC oscillations. For S=1.17, the VBB engulfs the centrebody and stabilizes the PVC mode. Therefore, in this case, PVC oscillations appear to be the flow response to broadband stochastic forcing of the time averaged flow by turbulence.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Case study: Prediction and field tests of railway noise and effects of a low-height noise barrier

2020 ◽  
Vol 68 (4) ◽  
pp. 303-314
Author(s):  
Yuna Park ◽  
Hyo-In Koh ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
...  
Keyword(s):  
High Speed ◽  
Field Tests ◽  
Residential Areas ◽  
Railway Systems ◽  
Railway Noise ◽  
Sound Levels ◽  
Noise Barrier ◽  
The Difference ◽  
Reduction Effect ◽  
The Impact

Railway noise is calculated to predict the impact of new or reconstructed railway tracks on nearby residential areas. The results are used to prepare adequate counter- measures, and the calculation results are directly related to the cost of the action plans. The calculated values were used to produce noise maps for each area of inter- est. The Schall 03 2012 is one of the most frequently used methods for the production of noise maps. The latest version was released in 2012 and uses various input para- meters associated with the latest rail vehicles and track systems in Germany. This version has not been sufficiently used in South Korea, and there is a lack of standard guidelines and a precise manual for Korean railway systems. Thus, it is not clear what input parameters will match specific local cases. This study investigates the modeling procedure for Korean railway systems and the differences between calcu- lated railway sound levels and measured values obtained using the Schall 03 2012 model. Depending on the location of sound receivers, the difference between the cal- culated and measured values was within approximately 4 dB for various train types. In the case of high-speed trains, the value was approximately 7 dB. A noise-reducing measure was also modeled. The noise reduction effect of a low-height noise barrier system was predicted and evaluated for operating railway sites within the frame- work of a national research project in Korea. The comparison of calculated and measured values showed differences within 2.5 dB.

The Impact of High-Speed Rail on the Spatial Structure of Chinese Urban Agglomerations

2020 ◽  
Vol 46 (3) ◽  
pp. 379-397
Author(s):  
Chunyang Wang
Keyword(s):  
High Speed ◽  
River Delta ◽  
City Size ◽  
High Speed Rail ◽  
Local Conditions ◽  
Urban Agglomerations ◽  
Large Cities ◽  
Spatial Systems ◽  
Economic Concentration ◽  
The Impact

This paper measures the spatial evolution of urban agglomerations to understand be er the impact of high-speed rail (HSR) construction, based on panel data from fi ve major urban agglomerations in China for the period 2004–2015. It is found that there are signi ficant regional diff erences of HSR impacts. The construction of HSR has promoted population and economic diff usion in two advanced urban agglomerations, namely the Yang e River Delta and Pearl River Delta, while promoting population and economic concentration in two relatively less advanced urban agglomerations, e.g. the middle reaches of the Yang e River and Chengdu–Chongqing. In terms of city size, HSR promotes the economic proliferation of large cities and the economic concentration of small and medium-sized cities along its routes. HSR networking has provided a new impetus for restructuring urban spatial systems. Every region should optimize the industrial division with strategic functions of urban agglomeration according to local conditions and accelerate the construction of inter-city intra-regional transport network to maximize the eff ects of high-speed rail across a large regional territory.

Dynamic model for high-speed rotors based on their experimental characterization

2017 ◽  
Vol 2 (4) ◽  
pp. 25
Author(s):  
L. A. Montoya ◽  
E. E. Rodríguez ◽  
H. J. Zúñiga ◽  
I. Mejía
Keyword(s):  
Dynamic Model ◽  
High Speed ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Experimental Characterization ◽  
Rotating Systems ◽  
Computing Performance ◽  
The Impact ◽  
Stiffness Distribution ◽  
Good Agreement

Rotating systems components such as rotors, have dynamic characteristics that are of great importance to understand because they may cause failure of turbomachinery. Therefore, it is required to study a dynamic model to predict some vibration characteristics, in this case, the natural frequencies and mode shapes (both of free vibration) of a centrifugal compressor shaft. The peculiarity of the dynamic model proposed is that using frequency and displacements values obtained experimentally, it is possible to calculate the mass and stiffness distribution of the shaft, and then use these values to estimate the theoretical modal parameters. The natural frequencies and mode shapes of the shaft were obtained with experimental modal analysis by using the impact test. The results predicted by the model are in good agreement with the experimental test. The model is also flexible with other geometries and has a great time and computing performance, which can be evaluated with respect to other commercial software in the future.

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