Investigation of the Unsteady Aerodynamics of an Annular Combustor Using PIV and LES

2008 ◽  
Author(s):  
Adrian Spencer ◽  
David Hollis ◽  
Sara Gashi
Keyword(s):  
Experimental Data ◽  
Boundary Conditions ◽  
Unsteady Aerodynamics ◽  
Predictive Ability ◽  
Fuel Injector ◽  
Predictive Tool ◽  
Annular Combustor ◽  
State Boundary ◽  
Inlet Conditions ◽  
Inflow Conditions

Experimental measurements have been carried out which have been used for specifying both boundary conditions of CFD predictions and for validation of the results. Combustor aerodynamics were therefore investigated in the same geometry, using LDA, PIV and LES. Three different LES simulations were performed in order to assess the flow field sensitivity to different boundary conditions. In the first run steady state boundary conditions are specified; in the second run, unsteady conditions at the injector exit and steady conditions in the annuli entry are specified; and in the third run unsteady boundary conditions at both injector exit and annuli entry are specified. A standard RANS simulation is also performed for comparison. The different simulations gave considerably different results. LES results with white noise scaled to give correct inlet turbulence intensities agree reasonably well with experimental data. With steady inflow conditions incorrect prediction of combustor aerodynamics resulted. Introduction of unsteady inflow conditions at the fuel injector exit plane were shown to have a significant effect on the flow interaction between the injector and the primary ports. LES is thus shown to be a good predictive tool for unsteady combustor flow fields. It is still questioned what level of fidelity is required in representing the inlet conditions to best use the predictive ability of LES. It offers significant improvement over standard RANS techniques but LES is more costly and requires detailed experimental data, used carefully, to correctly specify the inflow conditions.

Stochastic model of nonideal mixer. Boundary conditions in batch system

1984 ◽  
Vol 49 (2) ◽  
pp. 490-505
Author(s):  
Vladimír Kudrna ◽  
Pavel Hasal ◽  
Jiří Vlček
Keyword(s):  
Experimental Data ◽  
Stochastic Model ◽  
Boundary Conditions ◽  
Closed System ◽  
Batch System ◽  
Ideal Mixer

The earlier proposed general approach for description of the non-ideal mixer is coupled with corresponding boundary conditions for the closed system. Some simplifications in this procedure result in relations which are in agreement with experimental data.

Validating Numerical CFD Simulations With Experimental Data for Turbulence Phenomena in Axial Flow Gas Turbine Diffusers

2009 ◽  
Author(s):  
Farrokh Zarifi-Rad ◽  
Hamid Vajihollahi ◽  
James O’Brien
Keyword(s):  
Experimental Data ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Axial Flow ◽  
Experimental Results ◽  
Scale Model ◽  
Data Set ◽  
Pressure Profiles ◽  
Scale Models ◽  
Inlet Conditions

Scale models give engineers an excellent understanding of the aerodynamic behavior behind their design; nevertheless, scale models are time consuming and expensive. Therefore computer simulations such as Computational Fluid Dynamics (CFD) are an excellent alternative to scale models. One must ask the question, how close are the CFD results to the actual fluid behavior of the scale model? In order to answer this question the engineering team investigated the performance of a large industrial Gas Turbine (GT) exhaust diffuser scale model with performance predicted by commercially available CFD software. The experimental results were obtained from a 1:12 scale model of a GT exhaust diffuser with a fixed row of blades to simulate the swirl generated by the last row of turbine blades five blade configurations. This work is to validate the effect of the turbulent inlet conditions on an axial diffuser, both on the experimental front and on the numerical analysis approach. The object of this work is to bring forward a better understanding of velocity and static pressure profiles along the gas turbine diffusers and to provide an accurate experimental data set to validate the CFD prediction. For the CFD aspect, ANSYS CFX software was chosen as the solver. Two different types of mesh (hexagonal and tetrahedral) will be compared to the experimental results. It is understood that hexagonal (HEX) meshes are more time consuming and more computationally demanding, they are less prone to mesh sensitivity and have the tendancy to converge at a faster rate than the tetrahedral (TET) mesh. It was found that the HEX mesh was able to generate more consistent results and had less error than TET mesh.

The Heat Transport Capacity of Micro Heat Pipes

1998 ◽  
Vol 120 (4) ◽  
pp. 1064-1071 ◽  
Author(s):  
J. M. Ha ◽  
G. P. Peterson
Keyword(s):  
Experimental Data ◽  
Heat Pipe ◽  
Heat Transport ◽  
Heat Pipes ◽  
Original Model ◽  
Semiempirical Model ◽  
Transport Capacity ◽  
Predictive Tool ◽  
Maximum Heat ◽  
Micro Heat Pipes

The original analytical model for predicting the maximum heat transport capacity in micro heat pipes, as developed by Cotter, has been re-evaluated in light of the currently available experimental data. As is the case for most models, the original model assumed a fixed evaporator region and while it yields trends that are consistent with the experimental results, it significantly overpredicts the maximum heat transport capacity. In an effort to provide a more accurate predictive tool, a semi-empirical correlation has been developed. This modified model incorporates the effects of the temporal intrusion of the evaporating region into the adiabatic section of the heat pipe, which occurs as the heat pipe approaches dryout conditions. In so doing, the current model provides a more realistic picture of the actual physical situation. In addition to incorporating these effects, Cotter’s original expression for the liquid flow shape factor has been modified. These modifications are then incorporated into the original model and the results compared with the available experimental data. The results of this comparison indicate that the new semiempirical model significantly improves the correlation between the experimental and predicted results and more accurately represents the actual physical behavior of these devices.

scholarly journals Blind test comparison of the performance and wake flow between two in-line wind turbines exposed to different atmospheric inflow conditions

2016 ◽  
Author(s):  
Jan Bartl ◽  
Lars Sætran
Keyword(s):  
Wind Tunnel ◽  
Wind Turbines ◽  
Turbulence Intensity ◽  
Wake Flow ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Blind Test ◽  
The Mean ◽  
Inlet Conditions ◽  
Inflow Conditions

Abstract. This is a summary of the results of the fourth Blind test workshop which was held in Trondheim in October 2015. Herein, computational predictions on the performance of two in-line model wind turbines as well as the mean and turbulent wake flow are compared to experimental data measured at NTNU's wind tunnel. A detailed description of the model geometry, the wind tunnel boundary conditions and the test case specifications was published before the workshop. Expert groups within Computational Fluid Dynamics (CFD) were invited to submit predictions on wind turbine performance and wake flow without knowing the experimental results at the outset. The focus of this blind test comparison is to examine the model turbines' performance and wake development up until 9 rotor diameters downstream at three different atmospheric inflow conditions. Besides a spatially uniform inflow field of very low turbulence intensity (TI = 0.23 %) as well as high turbulence intensity (TI = 10.0 %), the turbines are exposed to a grid-generated atmospheric shear flow (TI = 10.1 %). Five different research groups contributed with their predictions using a variety of simulation models, ranging from fully resolved Reynolds Averaged Navier Stokes (RANS) models to Large Eddy Simulations (LES). For the three inlet conditions the power and the thrust force of the upstream turbine is predicted fairly well by most models, while the predictions of the downstream turbine's performance show a significantly higher scatter. Comparing the mean velocity profiles in the wake, most models approximate the mean velocity deficit level sufficiently well. However, larger variations between the models for higher downstream positions are observed. The prediction of the turbulence kinetic energy in the wake is observed to be very challenging. Both the LES model and the IDDES (Improved Delayed Detached Eddy Simulation) model, however, are consistently managing to provide fairly accurate predictions of the wake turbulence.

A Method of Measuring Turbulent Flow Structures With Particle Image Velocimetry and Incorporating Into Boundary Conditions of Large Eddy Simulations

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Puxuan Li ◽  
Steve J. Eckels ◽  
Garrett W. Mann ◽  
Ning Zhang
Keyword(s):  
Particle Image Velocimetry ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Particle Image ◽  
Advantages And Disadvantages ◽  
Eddy Simulation ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Inlet Conditions

The setup of inlet conditions for a large eddy simulation (LES) is a complex and important problem. Normally, there are two methods to generate the inlet conditions for LES, i.e., synthesized turbulence methods and precursor simulation methods. This study presents a new method for determining inlet boundary conditions of LES using particle image velocimetry (PIV). LES shows sensitivity to inlet boundary conditions in the developing region, and this effect can even extend into the fully developed region of the flow. Two kinds of boundary conditions generated from PIV data, i.e., steady spatial distributed inlet (SSDI) and unsteady spatial distributed inlet (USDI), are studied. PIV provides valuable field measurement, but special care is needed to estimate turbulent kinetic energy and turbulent dissipation rate for SSDI. Correlation coefficients are used to analyze the autocorrelation of the PIV data. Different boundary conditions have different influences on LES, and their advantages and disadvantages for turbulence prediction and static pressure prediction are discussed in the paper. Two kinds of LES with different subgrid turbulence models are evaluated: namely dynamic Smagorinsky–Lilly model (Lilly model) and wall modeled large eddy simulation (WMLES model). The performances of these models for flow prediction in a square duct are presented. Furthermore, the LES results are compared with PIV measurement results and Reynolds-stress model (RSM) results at a downstream location for validation.

Abstract T P113: Orpington Prognostic Scale: A Predictive Tool for Discharge Outcome in a Hyper Acute Stroke Unit

Stroke ◽  
2014 ◽  
Vol 45 (suppl_1) ◽  
Author(s):  
Sushmita Mohapatra ◽  
Amy M Jones
Keyword(s):  
Acute Stroke ◽  
Predictive Value ◽  
Stroke Unit ◽  
Predictive Ability ◽  
Inpatient Setting ◽  
Discharge Destination ◽  
Predictive Tool ◽  
Co Morbidity ◽  
Acute Stroke Unit ◽  
Rehabilitation Needs

Introduction: An accurate assessment of the severity of impairment and prediction of prognosis following stroke is important for determining rehabilitation needs of stroke patients. The study investigated the predictive ability of the Orpington Prognostic Scale (OPS) administered within 72 hours of stroke onset, in determining discharge destination post admission to a Hyper Acute Stroke Unit (HASU) in the United Kingdom. Method: Prospective analysis of OPS data were collected from 247 patients with confirmed diagnosis of stroke admitted to HASU. OPS scores were recorded between 0 to 72hours of admission and compared to discharge destination at 72 hours. Predictive ability of the tool and association with other variables were analysed using logistic regression and multivariate analysis. Results: Low OPS score (<3.2) had high positive predictive value (PPV 88.63%)for discharge home and high OPS score (>3.2) had high predictive value (PPV 98.39) for patients requiring further inpatient rehabilitation. OPS had high specificity and sensitivity for the above, independent of age, gender, type and site of stroke, stroke severity, previous social support and co-morbidity. Conclusions: OPS could be a valuable tool in predicting the discharge destination from a HASU and thereby facilitate the identification of early rehabilitation needs, 72 hours post stroke by predicting the need for further management. OPS < 3.2 were highly likely to go home with or without support/therapy. Whereas OPS > 3.2 were highly likely to require further medical/therapy input in an inpatient setting.

Utility of Neck, Height, and Tonsillar Size to Screen for Obstructive Sleep Apnea among Obese Youth

2017 ◽  
Vol 158 (4) ◽  
pp. 745-751 ◽  
Author(s):  
Indra Narang ◽  
Suhail Al-Saleh ◽  
Reshma Amin ◽  
Evan J. Propst ◽  
Saadoun Bin-Hasan ◽  
...  
Keyword(s):  
Obstructive Sleep Apnea ◽  
Sleep Apnea ◽  
Predictive Ability ◽  
Ambulatory Setting ◽  
Apnea Hypopnea Index ◽  
Predictive Tool ◽  
Anthropometric Measures ◽  
Cross Sectional ◽  
Obese Youth ◽  
Obstructive Sleep

Objectives To determine whether neck:height ratio combined with adenoid and tonsillar size is a good predictive tool for obstructive sleep apnea in obese youth. Study Design Cross-sectional study. Setting Sleep clinics at the Hospital for Sick Children, Toronto, Canada. Subjects and Methods Consented obese individuals aged 8 to 18 years were recruited between 2013 and 2015. Anthropometric measures were obtained by a trained research coordinator in a standardized manner. Otolaryngologists evaluated adenoid and tonsil sizes. Obstructive sleep apnea was diagnosed with an overnight polysomnogram as an obstructive apnea-hypopnea index ≥2. Multivariable logistic regressions investigated the relationship between potential predictors and obstructive sleep apnea. The C-statistic measured the predictive ability. Results Of the 53 subjects (median age, 13 years; 55% males), 28 (53%) were diagnosed with obstructive sleep apnea, with a median index of 10.6 per hour. In a logistic regression controlling for adenoid size, enlarged tonsils were significantly associated with the presence of obstructive sleep apnea ( P < .01). Adding neck:height ratio into the model improved the model predictive ability (C-index increased from 0.73 to 0.84). Controlling for tonsil and adenoid sizes, an increase in neck:height ratio was significantly associated with the presence of obstructive sleep apnea ( P = .01). Conclusion Our study suggests that neck:height ratio combined with tonsillar hypertrophy may have a strong predictive ability for obstructive sleep apnea and may be useful in an ambulatory setting to screen obese youth at high risk. These findings should be confirmed in a larger study.

Performance of Perforated Wall for the Conditioning of the Flow in an Ocean Basin

2008 ◽  
Author(s):  
Alexandre T. P. Alho ◽  
Sergio H. Sphaier ◽  
Carlos A. Levi Conceic¸a˜o ◽  
Paulo de Tarso T. Esperanc¸a
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Perforated Plate ◽  
Flow Characteristics ◽  
Ocean Basin ◽  
Main Flow ◽  
Generation System ◽  
Current Generation ◽  
Hydraulic Design ◽  
Inflow Conditions

This paper discusses the investigations conducted to develop the hydraulic design of the flow conditioner of the current generation system of LabOceano. The performance of different flow conditioner configurations were numerically investigated by means of computational fluid dynamics techniques. The numerical results were validated against experimental data, showing a good performance of the numerical model in predicting the main flow characteristics. It was observed that undesirable high angles of incidence of the flow occur upstream of the flow conditioner, indicating that the culvert geometry is not of much help to contribute to the conditioning of the flow. However, the results demonstrate that, in spite of such an adverse inflow conditions, the classical solution based on the perforated plate concept works very well.

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