Comparison of Numerical Modeling to Experimental Data in a Small Data Center Test Cell

2009 ◽  
Author(s):  
Ethan Cruz ◽  
Yogendra Joshi ◽  
Madhusudan Iyengar ◽  
Roger Schmidt
Keyword(s):  
Experimental Data ◽  
Data Center ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Computational Effort ◽  
Test Cell ◽  
Actual Data ◽  
Small Data ◽  
Air Cooling ◽  
Measured Temperature

Information Technology (IT) equipment compaction has become a significant air cooling challenge at the data center level. Computational Fluid Dynamics and Heat Transfer (CFD/HT) models have been employed as the dominant technique for the design and optimization of both new and existing data centers. Understanding the limitations of a CFD/HT models’ ability to predict the actual data center temperature field and flow characteristics becomes a critical component in optimizing the actual data center rather than optimizing the model of the data center. This is most important near the IT equipment where temperature and flow specifications from the IT equipment manufacturers must be maintained for reliable operation. This study is a continuation of earlier comparisons of CFD/HT models to experimentally measured temperature and flow fields in a small data center test cell. This study compares the experimentally collected data for three different layouts of perforated tiles to a CFD/HT model with seven turbulence models not previously evaluated. Insight into the location of the deviation between the different turbulence models and experimental data are discussed, along with the computational effort involved in running the CFD/HT models. It was found that the zero equation (or mixing length model) and the Spalart-Allamaras turbulence models produced the smallest deviations from experimental data, but the former required only a fifth of the computational effort of the latter. The laminar flow model required the least computational effort, running more than twice as fast as the zero equation turbulence model, and produced deviations similar to those of the six different k-ε turbulence models.

Comparison of Numerical Modeling to Experimental Data in a Small, Low Power Data Center Test Cell

2009 ◽  
Author(s):  
Ethan Cruz ◽  
Yogendra Joshi ◽  
Madhusudan Iyengar ◽  
Roger Schmidt
Keyword(s):  
Experimental Data ◽  
Laminar Flow ◽  
Data Center ◽  
Flow Model ◽  
Turbulence Models ◽  
Computational Effort ◽  
Test Cell ◽  
Air Cooling ◽  
Measured Temperature ◽  
Laminar Flow Model

As the performance of Information Technology (IT) equipment continues to rise, so do the power dissipated and overall power density. Air cooling this increasing power has proved a significant challenge even at the data center level. In order to combat this challenge, Computational Fluid Dynamics and Heat Transfer (CFD/HT) models have been employed as the dominant technique for the design and optimization of both new and existing data centers. This study is a continuation of earlier comparisons of CFD/HT models to experimentally measured temperature and flow fields in a small data center test cell. It compares previously unpublished experimentally collected data for the 11 kW dissipation cases using three different layouts of perforated tiles to a CFD/HT model using eight turbulence models and a laminar flow model. Insight into the location of the deviation between the different turbulence models and experimental data are discussed, along with the computational effort involved in running the CFD/HT models. It was found that the laminar flow model and the Spalart-Allamaras turbulence model produced the smallest deviations from experimental data, but the former required only one twentieth of the computational effort of the latter.

Inviscid and Viscous Numerical Models Compared to Experimental Data in a Small Data Center Test Cell

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Ethan Cruz ◽  
Yogendra Joshi
Keyword(s):  
Experimental Data ◽  
Data Center ◽  
Data Centers ◽  
Numerical Models ◽  
Computational Effort ◽  
Grid Size ◽  
Test Cell ◽  
Small Data ◽  
Air Cooling ◽  
Measured Temperature

Both localized power densities and overall power consumption within the data center continue to rise, following the same upward trend as the information technology (IT) equipment stored within the data center. Air cooling this increasing power has proved a significant challenge at both the IT equipment and data center level. In order to combat this challenge, computational fluid dynamics and heat transfer (CFD/HT) models have been employed as the dominant technique for the design and optimization of both new and existing data centers. This study is a continuation of earlier comparisons of CFD/HT models to experimentally measured temperature and flow fields in a small data center test cell. It compares an inviscid model, a laminar flow model, and three turbulence models to six sets of experimentally collected data. The six sets of data are from two different IT equipment rack power dissipations using three different layouts of perforated tiles. Insight into the location of the deviation between the different CFD/HT models and experimental data are discussed, along with the computational effort involved in running the models. A new grid analysis was performed on the different CFD/HT models in order to try to minimize computational effort. The inviscid model was able to run with a smaller grid size than the viscous models and even for the same size grid was found to run 30% faster than the fastest viscous model. Due to both the reduced grid size and computational effort (due to the simpler equation set), the inviscid model ran over thirty times faster than the next fastest model. The fact that the inviscid model ran the fastest is not surprising, however what was not expected is that the inviscid model was also found to have the smallest deviations from the experimental data for all six of the cases. This is most likely due to the arrangement of the data center test cell with the relatively few high velocity air jets and large open space around the IT equipment. More tightly packed data centers with higher air velocities and turbulent mixing conditions will certainly produce different results than those found in this study.

Numerical study of the flow field characteristics over a backward facing step using k-kl-ω turbulence model: comparison with different models

2018 ◽  
Vol 15 (1) ◽  
pp. 173-180 ◽  
Author(s):  
Yasser M. Ahmed ◽  
A.H. Elbatran
Keyword(s):  
Experimental Data ◽  
Fluid Mechanics ◽  
Turbulence Model ◽  
Flow Separation ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Numerical Results ◽  
Backward Facing Step ◽  
Content Type ◽  
Case Comparison

Purpose This paper aims to investigate numerically the turbulent flow characteristics over a backward facing step. Different turbulence models with hybrid computational grid have been used to study the detached flow structure in this case. Comparison between the numerical results and the available experiment data is carried out in the present study. The results of the different turbulence models were in a good agreement with the experimental results. The numerical results also concluded that the k-kl-ω turbulence model gave favorable results compared with the experiment. Design/methodology/approach It is very important to study the flow characteristics of detached flows. Therefore, the current study investigates numerically the flow characteristics in backward facing step by using two-, three- and seven-equation turbulence models in the finite volume code ANSYS Fluent. In addition, hybrid grid has been used to improve the capability of the unstructured mesh elements for predicting the flow separation in this case. Comparison between the different turbulence models and the available experimental data was done to find the most suitable turbulence model for simulating such cases of detached flows. Findings The present numerical simulations with the different turbulence models predicted efficiently the flow characteristics over the backward facing step. The transition k-kl-ω gave the best acceptable results compared with experimental data. This is a good concluded remark in the fields of fluid mechanics and hydrodynamics because the phenomenon of flow separation is not easy to be predicted numerically and can affect greatly on the predicted drag of moving bodies in many engineering applications. Originality/value The CFD results of using different turbulence models have been validated with the experimental work, and the results of k-kl-ω proven acceptable with flow characteristics. The results of the current study conclude that the use of k-kl-ω turbulence model will contribute towards a more efficient utilization in the fields of fluid mechanics and hydrodynamics.

Simulation of a 3D Axisymmetric Hill: Comparison of RANS and Hybrid RANS-LES Models

2016 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Experimental Data ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Leeward Side ◽  
Mean Flow ◽  
Rans Model ◽  
Reynolds Number Flow ◽  
Low Dissipation

Computational fluid dynamics (CFD) prediction of high Reynolds number flow over a 3D axisymmetric hill presents a unique set of challenges for turbulence models. The flow on the leeward side of the hill is characterized by the presence of complex vortical structures, unsteady wakes, and regions of boundary layer separation. As a result, traditional eddy-viscosity Reynolds-averaged Navier-Stokes (RANS) models have been found to perform poorly. Recent studies have focused on the use of Large Eddy Simulation (LES) and hybrid RANS-LES (HRL) methods to improve accuracy. In this study, the capability of a dynamic hybrid RANS-LES (DHRL) model to resolve the flow over a 3D axisymmetric hill is investigated and compared to numerical results using a traditional RANS model and a conventional hybrid RANS-LES model, and to experimental data. Results show that the RANS model fails to accurately predict the mean flow features in the wake region, which is in agreement with prior studies. The conventional HRL model provides better prediction of the flow characteristics but suffers from grid sensitivity and delayed transition to LES mode. The DHRL method provides the best agreement with experimental data overall and shows least sensitivity to grid resolution. Results also highlight the importance of using a low dissipation flux formulation for flow simulations in which a portion of the turbulence spectrum is resolved, including hybrid RANS-LES.

Prediction of Confined Three-Dimensional Impinging Flows With Various Turbulence Models

1992 ◽  
Vol 114 (2) ◽  
pp. 220-230 ◽  
Author(s):  
T. M. Liou ◽  
Y. H. Hwang ◽  
L. Chen
Keyword(s):  
Richardson Number ◽  
Laser Doppler Velocimetry ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Quantitative Agreement ◽  
Computational Effort ◽  
Main Flow ◽  
Inlet Velocity ◽  
Impinging Flows

This paper deals with three-dimensional, turbulent, confined impinging flows. Various turbulence models are examined with reported laser-Doppler velocimetry data and flow-visualization photographs. The turbulence models considered are the k–ε, k–ε with the Richardson number correction for swirling and recirculating flows (k–ε w/scm), algebraic Reynolds stress (k–ε–A), and modified k–kl models. The k–ε and k–ε–A models are found to be superior to the k–ε w/scm and modified k–kl models in predicting the main flow characteristics. The k–ε–A model provides a better quantitative agreement with the experimental data than can be achieved with the k–ε model, however, less computational effort is spent with the k–ε model than with the k–ε–A model. Also, the effect of the inlet velocity profile on the characteristics of the confined impinging flows is addressed in this study.

Improved CFD modeling of a small data center test cell

2010 ◽  
Author(s):  
Waleed A. Abdelmaksoud ◽  
H. Ezzat Khalifa ◽  
Thong Q. Dang ◽  
Roger R. Schmidt ◽  
Madhusudan Iyengar
Keyword(s):  
Data Center ◽  
Test Cell ◽  
Cfd Modeling ◽  
Small Data

Application of Wray–Agarwal Turbulence Model in Flow Simulation of a Centrifugal Pump With Semispiral Suction Chamber

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi ◽  
Ramesh K. Agarwal
Keyword(s):  
Experimental Data ◽  
Centrifugal Pump ◽  
Turbulence Model ◽  
Full Range ◽  
Flow Characteristics ◽  
Flow Simulation ◽  
Turbulence Models ◽  
Internal Flow ◽  
Energy Performance ◽  
Operating Conditions

Abstract The Wray–Agarwal (WA) turbulence model is selected to simulate the internal and external characteristics of a centrifugal pump with semispiral suction chamber; the numerical results are compared with the experimental data and computed results predicted by standard k–ε, renormalization group (RNG) k–ε, and shear stress transport (SST) k–ω turbulence models. The results show that the WA model could be effectively used to compute the energy performance of centrifugal pump under full range of operating conditions and gives higher accuracy than other models. Overall, the WA model shows closer similarity to the experimental data and gives more uniform flow field in the impeller region compared to that predicted by other models. In prediction of internal flow fields of the pump, overall the WA model is more accurate and efficient being a one-equation model. The control of undamped eddy viscosity variable R (= k/ω) in WA model does not allow the overestimation of turbulent kinetic energy and turbulent eddy frequency obtained with other models, which leads to its advantage in accurate prediction of both internal and external flow characteristics of centrifugal pump.

Two-dimensional numerical investigation of film cooling by a cool jet injected at various angles for different blowing ratios

2008 ◽  
Vol 222 (7) ◽  
pp. 1215-1224 ◽  
Author(s):  
S Bayraktar ◽  
T Yilmaz
Keyword(s):  
Experimental Data ◽  
Renormalization Group ◽  
Numerical Investigation ◽  
Turbulence Model ◽  
Film Cooling ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Cooling Efficiency ◽  
Two Dimensional ◽  
Transverse Jet

This paper presents the thermal and flow characteristics of a cold transverse jet, injected at five different angles (α = 30°, 45°, 60°, 75°, and 90°) into a hot crossflow with four different blowing ratios ( M = 0.1, 0.3, 0.5, and 0.8). Three turbulence models, namely, standard k−∊, renormalization group (RNG) k−∊, and realizable k−∊ are tested for obtaining the accurate turbulence model to predict the effectiveness of film cooling. The tested turbulence models were compared with available experimental data in the literature. The results evinced that the RNG k−∊ turbulence model is the most appropriate among the three. It is also observed that maximum cooling efficiency is obtained at α = 30° and M = 0.8.

Validation and Evaluation of Turbulence Models in Thermal Predictions of a Small Data Center Facility

2018 ◽  
Author(s):  
Beichao Hu ◽  
Long Phan ◽  
Cheng-Xian Lin
Keyword(s):  
Turbulence Model ◽  
Data Center ◽  
Data Centers ◽  
Cfd Simulation ◽  
Turbulence Models ◽  
Equation Model ◽  
Computational Time ◽  
Small Data ◽  
Resource Requirements ◽  
The Difference

Thermal management in data centers has become more and more important due to the rapid growth in power density in modern data centers. Computational fluid dynamics (CFD) is proved to be a very useful tool in data center design and analysis. However, the previous papers always utilize k-epsilon model, and has never studied on the effect of other turbulence models. This paper will demonstrate the difference between various turbulence models in terms of accuracy and computational time. The data center investigated in this paper has a floor area of 900 ft2 and comprises one rack, one CRAC unit, and several perforated tiles. This paper mainly investigates the effect of various turbulence models on CFD simulation in data center. The Turbulence model is believed to be a possible factor to improve the CFD results. The most suitable turbulence model will be identified based on a balance in both accuracy and computing resource requirements. Four turbulence models were investigated in this paper. The present investigation suggested that A&S 1-equation model yield the best accuracy and required the least computational time. Hence, 1-eqaution model should be the preferable turbulence model for CFD simulation in data center in the future.

scholarly journals Analysis of Flow Characteristics and Effects of Turbulence Models for the Butterfly Valve

2021 ◽  
Vol 11 (14) ◽  
pp. 6319
Author(s):  
Sung-Woong Choi ◽  
Hyoung-Seock Seo ◽  
Han-Sang Kim
Keyword(s):  
Turbulence Model ◽  
Dissipation Rate ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Flow Properties ◽  
Nominal Diameter ◽  
Large Pressure ◽  
Sst Model ◽  
Turbulence Effect ◽  
Valve Opening

In the present study, the flow characteristics of butterfly valves with different sizes DN 80 (nominal diameter: 76.2 mm), DN 262 (nominal diameter: 254 mm), DN 400 (nominal diameter: 406 mm) were numerically investigated under different valve opening percentages. Representative two-equation turbulence models of two-equation k-epsilon model of Launder and Sharma, two-equation k-omega model of Wilcox, and two-equation k-omega SST model of Menter were selected. Flow characteristics of butterfly valves were examined to determine turbulence model effects. It was determined that increasing turbulence effect could cause many discrepancies between turbulence models, especially in areas with large pressure drop and velocity increase. In addition, sensitivity analysis of flow properties was conducted to determine the effect of constants used in each turbulence model. It was observed that the most sensitive flow properties were turbulence dissipation rate (Epsilon) for the k-epsilon turbulence model and turbulence specific dissipation rate (Omega) for the k-omega turbulence model.

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