Thermal Characteristics of Open and Contained Data Center Cold Aisle

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Vaibhav K. Arghode ◽  
Vikneshan Sundaralingam ◽  
Yogendra Joshi ◽  
Wally Phelps
Keyword(s):  
Large Scale ◽  
Body Force ◽  
Field Measurements ◽  
Air Entrainment ◽  
Cfd Modeling ◽  
Force Model ◽  
Cold Air ◽  
Hot Air ◽  
Jump Model ◽  
Tile Surface

Cold aisle containment is used in raised floor, air cooled data centers to minimize direct mixing between the supplied cold air and the hot air exiting from the servers. The objective of such a system is to minimize the server inlet air temperatures. In this paper, large scale air temperature field measurements are performed to investigate the hot air entrainment characteristics in the cold aisle in both open and contained aisle conditions. Both under-provisioned and over-provisioned scenarios were examined. Thermal field measurements suggest significant improvement in the cold air delivery for the case with contained aisle as compared to open aisle. Even for an over-provisioned case with open aisle, hot air entrainment was observed from the aisle entrance; however, for the contained aisle condition, close to perfect cold air delivery to the racks was observed. For both under-provisioned and over-provisioned cases, the aisle containment tended to equalize the tile and rack air flow rates. Balance air is expected to be leaked into or out of the containment to makeup the flow rate difference for the contained aisle condition. The CFD modeling strategy at the aisle level is also discussed for open aisle condition. Our previous investigation for rack level modeling has shown that consideration of momentum rise above the tile surface improves the predictive capability as compared to the generally used porous jump model. The porous jump model only specifies a step pressure loss at the tile surface without any influence on flow field. The momentum rise above the tile surface was included using a modified body force model by artificially specifying a momentum source above the tile surface. The modified body force model suggested higher air entrainment and higher reach of cold air as compared to the porous jump model. The modified body force model was able to better capture hot air entrainment through aisle entrance and compared well with the experimental data for the end racks. The generally used porous jump model suggested lower hot air entrainment and under predicted the server inlet temperatures for end racks.

Room Level Modeling of Air Flow in a Contained Data Center Aisle

2014 ◽  
Vol 136 (1) ◽  
Author(s):  
Vaibhav K. Arghode ◽  
Yogendra Joshi
Keyword(s):  
Flow Field ◽  
Body Force ◽  
Air Flow ◽  
Air Entrainment ◽  
Field Investigation ◽  
Force Model ◽  
Hot Air ◽  
Jump Model ◽  
Cold Aisle Containment ◽  
Tile Surface

Cold aisle containment is used in air cooled data centers to minimize direct mixing between cold and hot air. Here, we present room level air flow field investigation for open, partially and fully contained cold aisles. Our previous investigation for rack level modeling has shown that consideration of momentum rise above the tile surface, due to acceleration of air through the pores, significantly improves the predictive capability as compared to the generally used porous jump model. The porous jump model only specifies a step pressure loss at the tile surface without any influence on the flow field. The momentum rise could be included by either directly resolving the tile's pore structure or by artificially specifying a momentum source above the tile surface. In the present work, a modified body force model is used to artificially specify the momentum rise above the tile surface. The modified body force model was validated against the experimental data as well as with the model resolving the tile pore geometry at the rack level and then implemented at the room level. With the modified body force model, much higher hot air entrainment and higher server inlet temperatures were predicted as compared to the porous jump model. Even when the rack air flow requirement is matched with the tile air flow supply, considerable hot air recirculation is predicted. With partial containment, where only a curtain at the top of the cold aisle is deployed and side doors are opened, improved cold air delivery is suggested.

Rack Level Modeling of Air Flow Through Perforated Tile in a Data Center

2012 ◽  
Author(s):  
Vaibhav K. Arghode ◽  
Pramod Kumar ◽  
Yogendra Joshi ◽  
Thomas S. Weiss ◽  
Gary Meyer
Keyword(s):  
Data Center ◽  
Body Force ◽  
Air Flow ◽  
The Body ◽  
Physical Models ◽  
Cfd Modeling ◽  
Computational Time ◽  
Force Model ◽  
Flow Through ◽  
Tile Surface

Effective air flow distribution through perforated tiles is required to efficiently cool servers in a raised floor data center. We present detailed computational fluid dynamics (CFD) modeling of air flow through a perforated tile and its entrance to the adjacent server rack. The realistic geometrical details of the perforated tile, as well as of the rack are included in the model. Generally models for air flow through perforated tiles specify a step pressure loss across the tile surface, or porous jump model based on the tile porosity. An improvement to this includes a momentum source specification above the tile to simulate the acceleration of the air flow through the pores, or body force model. In both of these models geometrical details of tile such as pore locations and shapes are not included. More details increase the grid size as well as the computational time. However, the grid refinement can be controlled to achieve balance between the accuracy and computational time. We compared the results from CFD using geometrical resolution with the porous jump and body force model solution as well as with the measured flow field using Particle Image Velocimetry (PIV) experiments. We observe that including tile geometrical details gives better results as compared to elimination of tile geometrical details and specifying physical models across and above the tile surface. A modification to the body force model is also suggested and improved results were achieved.

Rack Level Modeling of Air Flow Through Perforated Tile in a Data Center

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Vaibhav K. Arghode ◽  
Pramod Kumar ◽  
Yogendra Joshi ◽  
Thomas Weiss ◽  
Gary Meyer
Keyword(s):  
Data Center ◽  
Body Force ◽  
Air Flow ◽  
The Body ◽  
Physical Models ◽  
Cfd Modeling ◽  
Computational Time ◽  
Force Model ◽  
Flow Through ◽  
Tile Surface

Effective air flow distribution through perforated tiles is required to efficiently cool servers in a raised floor data center. We present detailed computational fluid dynamics (CFD) modeling of air flow through a perforated tile and its entrance to the adjacent server rack. The realistic geometrical details of the perforated tile, as well as of the rack are included in the model. Generally, models for air flow through perforated tiles specify a step pressure loss across the tile surface, or porous jump model based on the tile porosity. An improvement to this includes a momentum source specification above the tile to simulate the acceleration of the air flow through the pores, or body force model. In both of these models, geometrical details of tile such as pore locations and shapes are not included. More details increase the grid size as well as the computational time. However, the grid refinement can be controlled to achieve balance between the accuracy and computational time. We compared the results from CFD using geometrical resolution with the porous jump and body force model solution as well as with the measured flow field using particle image velocimetry (PIV) experiments. We observe that including tile geometrical details gives better results as compared to elimination of tile geometrical details and specifying physical models across and above the tile surface. A modification to the body force model is also suggested and improved results were achieved.

Modified Body Force Model for Air Flow Through Perforated Floor Tiles in Data Centers

2016 ◽  
Vol 138 (3) ◽  
Author(s):  
Vaibhav K. Arghode ◽  
Yogendra Joshi
Keyword(s):  
Flow Field ◽  
Pore Structure ◽  
Data Centers ◽  
Body Force ◽  
Air Flow ◽  
Source Region ◽  
Pore Geometry ◽  
Force Model ◽  
Floor Tiles ◽  
Tile Surface

Generally, porous jump (PJ) model is used for rapid air flow simulations (without resolving the tile pore structure) through perforated floor tiles in data centers. The PJ model only specifies a step pressure loss across the tile surface, without any influence on the flow field. However, in reality, the downstream flow field is affected because of the momentum rise of air due to acceleration through the pores, and interaction of jets emerging from the pores. The momentum rise could be captured by either directly resolving the tile pore structure (geometrical resolution (GR) model) or simulated by specifying a momentum source above the tile surface (modified body force (MBF) model). Note that specification of momentum source obviates the need of resolving the tile pore geometry and, hence, requires considerably low computational effort. In previous investigations, the momentum source was imposed in a region above the tile surface whose width and length were same as the tile dimensions with a preselected height. This model showed improved prediction with the experimental data, as well as with the model resolving the tile pore geometry. In the present investigation, we present an analysis for obtaining the momentum source region dimensions and other associated input variables so that the MBF model can be applied for general cases. The results from this MBF model were compared with the GR model and good agreement was obtained.

Numerical investigation of total temperature distortion problem in a multistage fan based on body force approach

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Jin Guo ◽  
Jun Hu ◽  
Baofeng Tu
Keyword(s):  
Steady State ◽  
Total Pressure ◽  
High Speed ◽  
Large Scale ◽  
Body Force ◽  
Present Model ◽  
Force Model ◽  
Flow Feature ◽  
Total Temperature ◽  
Large Scale Flow

AbstractThis paper applies a body force model developed recently to investigate the interaction between total temperature distortion and a multistage fan. The off-design performance of the fan shows the reasonable predicting accuracy and supports the present model is applicable for high-speed multistage machines. The transfer behaviors of 90° steady-state circumferential total temperature distortion as well as combined total pressure and total temperature distortion in the multistage environment are captured successfully by the model. The mechanism of the phase shift of the high temperature sector is discussed by the model to advance the understanding of the total temperature distortion problem. The results reveal that the large-scale flow feature of total temperature distortion in the multistage environment can be capably quantified by the present body force model with the acceptable computational consumption.

scholarly journals Combined Block Adjustment for Optical Satellite Stereo Imagery Assisted by Spaceborne SAR and Laser Altimetry Data

2021 ◽  
Vol 13 (16) ◽  
pp. 3062
Author(s):  
Guo Zhang ◽  
Boyang Jiang ◽  
Taoyang Wang ◽  
Yuanxin Ye ◽  
Xin Li
Keyword(s):  
Large Scale ◽  
Satellite Image ◽  
Field Measurements ◽  
High Elevation ◽  
Global Scale ◽  
Stereo Image ◽  
Image Process ◽  
Control Points ◽  
Altimetry Data ◽  
Laser Altimetry

To ensure the accuracy of large-scale optical stereo image bundle block adjustment, it is necessary to provide well-distributed ground control points (GCPs) with high accuracy. However, it is difficult to acquire control points through field measurements outside the country. Considering the high planimetric accuracy of spaceborne synthetic aperture radar (SAR) images and the high elevation accuracy of satellite-based laser altimetry data, this paper proposes an adjustment method that combines both as control sources, which can be independent from GCPs. Firstly, the SAR digital orthophoto map (DOM)-based planar control points (PCPs) acquisition is realized by multimodal matching, then the laser altimetry data are filtered to obtain laser altimetry points (LAPs), and finally the optical stereo images’ combined adjustment is conducted. The experimental results of Ziyuan-3 (ZY-3) images prove that this method can achieve an accuracy of 7 m in plane and 3 m in elevation after adjustment without relying on GCPs, which lays the technical foundation for a global-scale satellite image process.

scholarly journals Computational Modeling of Vortex Generators for Turbomachinery

2002 ◽  
Author(s):  
R. V. Chima
Keyword(s):  
Computational Models ◽  
Body Force ◽  
Secondary Flows ◽  
The Body ◽  
Vortex Generators ◽  
Force Model ◽  
Suction Surface ◽  
Near Surface ◽  
Compressor Rotor ◽  
Surface Particle

In this work computational models were developed and used to investigate applications of vortex generators (VGs) to turbomachinery. The work was aimed at increasing the efficiency of compressor components designed for the NASA Ultra Efficient Engine Technology (UEET) program. Initial calculations were used to investigate the physical behavior of VGs. A parametric study of the effects of VG height was done using 3-D calculations of isolated VGs. A body force model was developed to simulate the effects of VGs without requiring complicated grids. The model was calibrated using 2-D calculations of the VG vanes and was validated using the 3-D results. Then three applications of VGs to a compressor rotor and stator were investigated: 1. The results of the 3-D calculations were used to simulate the use of small casing VGs used to generate rotor preswirl or counterswirl. Computed performance maps were used to evaluate the effects of VGs. 2. The body force model was used to simulate large partspan splitters on the casing ahead of the stator. Computed loss buckets showed the effects of the VGs. 3. The body force model was also used to investigate the use of tiny VGs on the stator suction surface for controlling secondary flows. Near-surface particle traces and exit loss profiles were used to evaluate the effects of the VGs.

Three body force model for lattice dynamics of copper

1986 ◽  
Vol 57 (8) ◽  
pp. 559-562 ◽  
Author(s):  
H. Nait-Laziz ◽  
K.K. Chopra
Keyword(s):  
Lattice Dynamics ◽  
Body Force ◽  
Force Model ◽  
Three Body

scholarly journals Atmospheric tropical modes are important drivers of Sahelian springtime heatwaves

2020 ◽  
Author(s):  
Kiswendsida H. Guigma ◽  
Françoise Guichard ◽  
Martin Todd ◽  
Philippe Peyrille ◽  
Yi Wang
Keyword(s):  
Large Scale ◽  
Geographic Location ◽  
Longwave Radiation ◽  
Potential Predictability ◽  
Modes Of Variability ◽  
Physical Mechanisms ◽  
Hot Air ◽  
Western Sahel ◽  
Maximum Temperatures ◽  
Sahel Region

AbstractHeatwaves pose a serious threat to human health worldwide but remain poorly documented over Africa. This study uses mainly the ERA5 dataset to investigate their large-scale drivers over the Sahel region during boreal spring, with a focus on the role of tropical modes of variability including the Madden–Julian Oscillation (MJO) and the equatorial Rossby and Kelvin waves. Heatwaves were defined from daily minimum and maximum temperatures using a methodology that retains only intraseasonal scale events of large spatial extent. The results show that tropical modes have a large influence on the occurrence of Sahelian heatwaves, and, to a lesser extent, on their intensity. Depending on their convective phase, they can either increase or inhibit heatwave occurrence, with the MJO being the most important of the investigated drivers. A certain sensitivity to the geographic location and the diurnal cycle is observed, with nighttime heatwaves more impacted by the modes over the eastern Sahel and daytime heatwaves more affected over the western Sahel. The examination of the physical mechanisms shows that the modulation is made possible through the perturbation of regional circulation. Tropical modes thus exert a control on moisture and the subsequent longwave radiation, as well as on the advection of hot air. A detailed case study of a major event, which took place in April 2003, further supports these findings. Given the potential predictability offered by tropical modes at the intraseasonal scale, this study has key implications for heatwave risk management in the Sahel.

Snowflakes in the atmospheric surface layer: observation of particle–turbulence dynamics

2017 ◽  
Vol 814 ◽  
pp. 592-613 ◽  
Author(s):  
Andras Nemes ◽  
Teja Dasari ◽  
Jiarong Hong ◽  
Michele Guala ◽  
Filippo Coletti
Keyword(s):  
Large Scale ◽  
Isotropic Turbulence ◽  
Volume Fraction ◽  
Response Times ◽  
Field Measurements ◽  
Stokes Number ◽  
Inertial Particles ◽  
Natural Setting ◽  
Scale Particle ◽  
Particle Imaging

We report on optical field measurements of snow settling in atmospheric turbulence at $Re_{\unicode[STIX]{x1D706}}=940$. It is found that the snowflakes exhibit hallmark features of inertial particles in turbulence. The snow motion is analysed in both Eulerian and Lagrangian frameworks by large-scale particle imaging, while sonic anemometry is used to characterize the flow field. Additionally, the snowflake size and morphology are assessed by digital in-line holography. The low volume fraction and mass loading imply a one-way interaction with the turbulent air. Acceleration probability density functions show wide exponential tails consistent with laboratory and numerical studies of homogeneous isotropic turbulence. Invoking the assumption that the particle acceleration has a stronger dependence on the Stokes number than on the specific features of the turbulence (e.g. precise Reynolds number and large-scale anisotropy), we make inferences on the snowflakes’ aerodynamic response time. In particular, we observe that their acceleration distribution is consistent with that of particles of Stokes number in the range $St=0.1{-}0.4$ based on the Kolmogorov time scale. The still-air terminal velocities estimated for the resulting range of aerodynamic response times are significantly smaller than the measured snow particle fall speed. This is interpreted as a manifestation of settling enhancement by turbulence, which is observed here for the first time in a natural setting.

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