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.

Effect of Rack Models and Buoyancy Forces on a Small Data Center Facility

2019 ◽  
Author(s):  
Beichao Hu ◽  
Long Phan ◽  
Cheng-Xian Lin
Keyword(s):  
Data Center ◽  
Buoyancy Force ◽  
Data Centers ◽  
Cfd Simulation ◽  
Early Stage ◽  
Black Box ◽  
Ease Of Use ◽  
Box Model ◽  
Small Data ◽  
Buoyancy Forces

Abstract Due to the rapid growth of the power density in data centers, the thermal management of the data center has become more and more important. Computational Fluid Dynamics has been proven to be one of the most effective tools in the design and analysis in data centers due to its ease of use and fast prediction in data centers. Due to the large size of a data center facility, one of the most challenging tasks in the data center CFD simulation is to establish simplified models to provide a fast but accurate prediction for both the temperature and flow field in data centers. In the past few years, people have proposed many tile models specifically to simulate the jet effect of the perforated tile. However, other aspects of the simulation were still in the early stage, e.g. rack models and the effect of buoyancy forces. This paper mainly studied the effect of the three rack models, which were Black Box Model, Modified Black Box Model, and Volumetric Heat Model. The effects of the buoyancy force were also studied. The result showed that buoyancy force had a huge impact on the simulation result, while the three rack models investigated had little difference.

scholarly journals New Data Center Performance Index: Perfect Design Data Center—PDD

Climate ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 110
Author(s):  
Alexandre F. Santos ◽  
Pedro D. Gaspar ◽  
Heraldo J. L. de Souza
Keyword(s):  
Data Center ◽  
Air Conditioning ◽  
Data Centers ◽  
Current Method ◽  
Energy Usage ◽  
Design Data ◽  
The Difference ◽  
Power Usage Effectiveness ◽  
Approximate Result ◽  
Classification Table

Data Centers (DC) are specific buildings that require large infrastructures to store all the information needed by companies. All data transmitted over the network is stored on CDs. By the end of 2020, Data Centers will grow 53% worldwide. There are methodologies that measure the efficiency of energy consumption. The most used metric is the Power Usage Effectiveness (PUE) index, but it does not fully reflect efficiency. Three DC’s located at the cities of Curitiba, Londrina and Iguaçu Falls (Brazil) with close PUE values, are evaluated in this article using the Energy Usage Effectiveness Design (EUED) index as an alternative to the current method. EUED uses energy as a comparative element in the design phase. Infrastructure consumption is the sum of energy with Heating, Ventilating and Air conditioning (HVAC) equipment, equipment, lighting and others. The EUED values obtained were 1.245 (kWh/yr)/(kWh/yr), 1.313 (kWh/yr)/(kWh/yr) and 1.316 (kWh/yr)/(kWh/yr) to Curitiba, Londrina and Iguaçu Falls, respectively. The difference between the EUED and the PUE Constant External Air Temperature (COA) is 16.87% for Curitiba, 13.33% for Londrina and 13.30% for Iguaçu Falls. The new Perfect Design Data center (PDD) index prioritizes efficiency in increasing order is an easy index to interpret. It is a redefinition of EUED, given by a linear equation, which provides an approximate result and uses a classification table. It is a decision support index for the location of a Data Center in the project phase.

Prediction of a Laminar Separation Bubble Over a Controlled-Diffusion Compressor Blade

2000 ◽  
Author(s):  
G. V. Hobson ◽  
S. Weber
Keyword(s):  
Turbulence Model ◽  
Separation Bubble ◽  
Turbulence Models ◽  
Leading Edge ◽  
Equation Model ◽  
Implicit Time ◽  
Controlled Diffusion ◽  
Time Marching ◽  
The One ◽  
Edge Separation

The paper describes the comparison of the prediction of the flow through a cascade of controlled-diffusion compressor blades with two Navier-Stokes solvers. Both codes solved the thin-layer N-S equations, however; one code performed implicit time marching whereas the other performed explicit time marching. Flow predictions were accomplished with the implicit code using the algebraic turbulence model of Baldwin and Lomax and the one-equation model of Spalart and Allmaras, while predictions were made with the explicit code using the two-equation model by Wilcox. Predictions were made of the detailed laser-anemometry measurements of the flow field taken previously in a low-speed cascade wind tunnel. Comparisons were also made with the experimentally measured blade surface pressures and flow visualization of the extent of the laminar leading edge separation bubble. The one-equation turbulence model was combined with an intermittency based transition-length model for comparisons with fully turbulent calculations. Both codes predicted the leading-edge separation bubble satisfactorily when using higher order turbulence models.

Experimentally Verified Transient Models of Data Center Crossflow Heat Exchangers

2014 ◽  
Author(s):  
Tianyi Gao ◽  
Bahgat Sammakia ◽  
James Geer ◽  
Milnes David ◽  
Roger Schmidt
Keyword(s):  
Heat Exchanger ◽  
Data Center ◽  
Heat Exchangers ◽  
Distribution Systems ◽  
Data Centers ◽  
Computational Time ◽  
Cooling Systems ◽  
Rear Door ◽  
Compact Models ◽  
Liquid Heat

Heat exchangers are key components that are commonly used in data center cooling systems. Rear door heat exchangers, in-row coolers, overhead coolers and fully contained cabinets are some examples of liquid and hybrid cooling systems used in data centers. A liquid to liquid heat exchanger is one of the main components of the Coolant Distribution Unit (CDU), which supplies chilled water to the heat exchangers mentioned above. Computer Room Air Conditioner (CRAC) units also consist of liquid to air cross flow heat exchangers. Optimizing the energy use and the reliability of IT equipment in data centers requires Computational Fluid Dynamics (CFD) tools that can accurately model data centers for both the steady state and dynamic operations. Typically, data centers operate in dynamic conditions due to workload allocations that change both spatially and temporally. Additional dynamic situations may also arise due to failures in the thermal management and electrical distribution systems. In the computational simulation, individual component models, such as transient heat exchanger models, are therefore needed. It is also important to develop simple, yet accurate, compact models for components, such as heat exchangers, to reduce the computational time without decreasing simulation accuracy. In this study, a method for modeling compact transient heat exchangers using CFD code is presented. The method describes an approach for installing thermal dynamic heat exchanger models in CFD codes. The transient effectiveness concept and model are used in the development of the methodology. Heat exchanger CFD compact models are developed and tested by comparing them with full thermal dynamic models, and also with experimental measurements. The transient responses of the CFD model are presented for step and ramp change in flow rates of the hot and cold fluids, as well as step, ramp, and exponential variation in the inlet temperature. Finally, some practical dynamic scenarios involving IBM buffer liquid to liquid heat exchanger, rear door heat exchanger, and CRAC unit, are parametrically modeled to test the developed methodology. It is shown that the compact heat exchanger model can be used to successfully predict dynamic scenarios in typical data centers.

scholarly journals Prediction of Turbine Blade Passage Heat Transfer Using a Zero and a Two-Equation Turbulence Model

1994 ◽  
Author(s):  
Ali A. Ameri ◽  
Andrea Arnone
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Algebraic Model ◽  
Equation Model ◽  
Accurate Solution ◽  
Bypass Transition ◽  
Transfer Rates ◽  
Blade Passage

Predictions of the heat transfer rates on the hot surfaces of a turbine cascade blade passage as influenced by the turbulence models was examined. A zero equation turbulence model supplemented by a bypass transition model and a two equation low Reynolds number model were chosen for this study. The experimental data of Graziani et. al. were used for comparison. The comparisons suggest that at least for the experimental data considered in this work the use of a two-equation model does not provide an overall more accurate solution than the zero equation model. This conclusion is strengthened if one takes into account the relative economy of computations with the algebraic model.

scholarly journals On turbulence models and lidar measurements for wind turbine control

2021 ◽  
Vol 6 (6) ◽  
pp. 1491-1500
Author(s):  
Liang Dong ◽  
Wai Hou Lio ◽  
Eric Simley
Keyword(s):  
Wind Turbine ◽  
Turbulence Model ◽  
Spatial Coherence ◽  
Turbulence Models ◽  
Lidar Measurement ◽  
Wind Turbine Control ◽  
Comprehensive Information ◽  
The Difference ◽  
Turbine Design ◽  
The Impact

Abstract. To provide comprehensive information that will assist in making decisions regarding the adoption of lidar-assisted control (LAC) in wind turbine design, this paper investigates the impact of different turbulence models on the coherence between the rotor-effective wind speed and lidar measurement. First, the differences between the Kaimal and Mann models are discussed, including the power spectrum and spatial coherence. Next, two types of lidar systems are examined to analyze the lidar measurement coherence based on commercially available lidar scan patterns. Finally, numerical simulations have been performed to compare the lidar measurement coherence for different rotor sizes. This work confirms the association between the measurement coherence and the turbulence model. The results indicate that the lidar measurement coherence with the Mann turbulence model is lower than that with the Kaimal turbulence model. In other words, the potential value creation of LAC based on simulations during the wind turbine design phase, evaluated using the Kaimal turbulence model, will be diminished if the Mann turbulence model is used instead. In particular, the difference in coherence is more significant for larger rotors. As a result, this paper suggests that the impacts of different turbulence models should be considered uncertainties while evaluating the benefits of LAC.

CFD Simulation of Gasoline Compression Ignition

2014 ◽  
Author(s):  
Janardhan Kodavasal ◽  
Christopher Kolodziej ◽  
Stephen Ciatti ◽  
Sibendu Som
Keyword(s):  
Turbulence Model ◽  
Cfd Simulation ◽  
Turbulence Models ◽  
Kinetic Mechanism ◽  
Chemical Kinetic ◽  
Combustion Model ◽  
Low Temperature Combustion ◽  
Compression Ignition ◽  
Simulation Results ◽  
The Impact

Gasoline compression ignition (GCI) is a low temperature combustion (LTC) concept that has been gaining increasing interest over the recent years owing to its potential to achieve diesel-like thermal efficiencies with significantly reduced engine-out nitrogen oxides (NOx) and soot emissions compared to diesel engines. In this work, closed-cycle computational fluid dynamics (CFD) simulations are performed of this combustion mode using a sector mesh in an effort to understand effects of model settings on simulation results. One goal of this work is to provide recommendations for grid resolution, combustion model, chemical kinetic mechanism, and turbulence model to accurately capture experimental combustion characteristics. Grid resolutions ranging from 0.7 mm to 0.1 mm minimum cell sizes were evaluated in conjunction with both Reynolds averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) based turbulence models. Solution of chemical kinetics using the multi-zone approach is evaluated against the detailed approach of solving chemistry in every cell. The relatively small primary reference fuel (PRF) mechanism (48 species) used in this study is also evaluated against a larger 312-species gasoline mechanism. Based on these studies the following model settings are chosen keeping in mind both accuracy and computation costs — 0.175 mm minimum cell size grid, RANS turbulence model, 48-species PRF mechanism, and multi-zone chemistry solution with bin limits of 5 K in temperature and 0.05 in equivalence ratio. With these settings, the performance of the CFD model is evaluated against experimental results corresponding to a low load start of injection (SOI) timing sweep. The model is then exercised to investigate the effect of SOI on combustion phasing with constant intake valve closing (IVC) conditions and fueling over a range of SOI timings to isolate the impact of SOI on charge preparation and ignition. Simulation results indicate that there is an optimum SOI timing, in this case −30°aTDC (after top dead center), which results in the most stable combustion. Advancing injection with respect to this point leads to significant fuel mass burning in the colder squish region, leading to retarded phasing and ultimately misfire for SOI timings earlier than −42°aTDC. On the other hand, retarding injection beyond this optimum timing results in reduced residence time available for gasoline ignition kinetics, and also leads to retarded phasing, with misfire at SOI timings later than −15°aTDC.

scholarly journals CFD flow analysis in the centrifugal vortex pump

2014 ◽  
Vol 24 (3) ◽  
pp. 545-562 ◽  
Author(s):  
Tihomir Mihalić ◽  
Zvonimir Guzović ◽  
Andrej Predin
Keyword(s):  
Numerical Model ◽  
Turbulence Model ◽  
Control Volume ◽  
Flow Analysis ◽  
Turbulence Models ◽  
Numerical Control ◽  
Computational Time ◽  
Back Side ◽  
Centrifugal Pumps ◽  
Content Type

Purpose – Aging of the oil wells leads to a decrease in reservoir pressure and also to an increase in the water, gas and abrasive particles content. Therefore, there is a need for the oil pumps exploitation characteristics improvements. This paper aims to generate a valuable numerical model which will provide a useful tool to study various cases. Design/methodology/approach – Computational fluid dynamics (CFD) analysis of the generation of so-called coherent structures of eddies and turbulence in the peripheral area of the vortex rotor mounted at the back side of centrifugal rotor was undertaken. After detailed analysis of the influence of the used turbulence models on the results, a hybrid turbulent model Detached Eddies Simulation (DES) was chosen as the most suitable. Findings – Numerical control volume method with unsteady solver and DES turbulence model was proven to be valuable tool for flow analysis in the centrifugal pumps. Having in mind that DES turbulence model consumes much less computational time than large eddies turbulence model, this is a very useful fact that resulted from this research. Practical implications – The proven numerical model is robust and reliable enough to become a standard method in simulating flow and other physical phenomena occurring in centrifugal pumps and similar turbo machines. This makes it possible to easily research different factors that influence their performances. Originality/value – Comprehensive experimental and CFD study was performed which made it possible to conduct detailed validation and verification of described CFD model.

The Influence of Turbulence Model Selection and Leakage Considerations on CFD Simulation Results for a Centrifugal Pump

2012 ◽  
Vol 594-597 ◽  
pp. 1940-1944
Author(s):  
Han Liu ◽  
Hua Chen Pan
Keyword(s):  
Numerical Simulation ◽  
Model Selection ◽  
Centrifugal Pump ◽  
Turbulence Model ◽  
Cfd Simulation ◽  
Turbulence Models ◽  
Leakage Flow ◽  
Pump Performance ◽  
Simulation Results

A commercial CFD software was used to simulate and predict a centrifugal pump performance. In this paper，the influences on the numerical simulation results using different turbulence models and different leakage flow assumptions were studied. The simulations are based on RANS with the and SST turbulence models. It is found that SST turbulence is better. Also the influence of the leakage flow was studied.

3-D CFD Simulation of the Airflow over a Gable Roof with Different Elevations

2015 ◽  
Vol 769 ◽  
pp. 229-234
Author(s):  
Juraj Jr. Kralik
Keyword(s):  
Wind Tunnel ◽  
Turbulence Model ◽  
Cfd Simulation ◽  
Wind Tunnel Test ◽  
Turbulence Models ◽  
Accurate Method ◽  
Navier Stokes ◽  
Ansys Fluent ◽  
Pressure Coefficients ◽  
Gable Roof

The pressure coefficients on duo-pitched roofs of separated buildings are well described by several standards. Nowadays, there are various commercial or non-commercial programs which can predict the pressure coefficients. However, the most accurate method is to perform a wind tunnel test. The aim of this paper is to simulate the airflow over a gable roof with different elevations under ANSYS Fluent 14.0 program. Examined elevations of the gable roof are 5°, 15° and 30°. Classical two equation k-ε turbulence models based on Reynolds Averaged Navier-Stokes (RANS) equations simulation were performed. Performance of each turbulence model with the increasing angel of the roof was compared.

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