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.

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.

Calculation of Flow Instability Inception in High Speed Axial Compressors

2014 ◽  
Author(s):  
Xiaohua Liu ◽  
Yanpei Zhou ◽  
Xiaofeng Sun ◽  
Dakun Sun
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Body Force ◽  
Present Model ◽  
Flow Instability ◽  
Tip Clearance ◽  
Force Model ◽  
Fine Grid ◽  
Stall Margin ◽  
Onset Point

This paper applies a theoretical model developed recently to calculate the flow instability inception point in axial high speed compressors system. After the mean flow field is computed by steady CFD simulation, a body force approach, which is a function of flow field data and comprises of one inviscid part and the other viscid part, is taken to duplicate the physical sources of flow turning and loss. Further by applying appropriate boundary conditions and spectral collocation method, a group of homogeneous equations will yield from which the stability equation can be derived. The singular value decomposition method is adopted over a series of fine grid points in frequency domain, and the onset point of flow instability can be judged by the imaginary part of the resultant eigenvalue. The first assessment is to check the applicability of the present model on calculating the stall margin of one single stage transonic compressors at 85% rotational speed. The reasonable prediction accuracy validates that this model can provide an unambiguous judgment on stall inception without numerous requirements of empirical relations of loss and deviation angle. It could possibly be employed to check over-computed stall margin during the design phase of new high speed fan/compressors. The following validation case is conducted to study the nontrivial role of tip clearance in rotating stall, and a parameter study is performed to investigate the effects of end wall body force coefficient on stall onset point calculation. It is verified that the present model could qualitatively predict the reduced stall margin by assuming a simplified body force model which represents the response of a large tip clearance on the unsteady flow field.

Calculation of Flow Instability Inception in High Speed Axial Compressors Based on an Eigenvalue Theory

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Xiaohua Liu ◽  
Yanpei Zhou ◽  
Xiaofeng Sun ◽  
Dakun Sun
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Body Force ◽  
Present Model ◽  
Flow Instability ◽  
Tip Clearance ◽  
Force Model ◽  
Fine Grid ◽  
Stall Margin ◽  
Onset Point

This paper applies a theoretical model developed recently to calculate the flow instability inception point in axial high speed compressors system with tip clearance. After the mean flow field is computed by 3D steady computational fluid dynamics (CFD) simulation, a body force approach, which is a function of flow field data and comprises of one inviscid part and the other viscid part, is taken to duplicate the physical sources of flow turning and loss. Further by applying appropriate boundary conditions and spectral collocation method, a group of homogeneous equations will yield from which the stability equation can be derived. The singular value decomposition (SVD) method is adopted over a series of fine grid points in frequency domain, and the onset point of flow instability can be judged by the imaginary part of the resultant eigenvalue. The first assessment is to check the applicability of the present model on calculating the stall margin of one single stage transonic compressors at 85% rotational speed. The reasonable prediction accuracy validates that this model can provide an unambiguous judgment on stall inception without numerous requirements of empirical relations of loss and deviation angle. It could possibly be employed to check overcomputed stall margin during the design phase of new high speed compressors. The following validation case is conducted to study the nontrivial role of tip clearance in rotating stall, and a parameter study is performed to investigate the effects of end wall body force coefficient on stall onset point calculation. It is verified that the present model could qualitatively predict the reduced stall margin by assuming a simplified body force model which represents the response of a large tip clearance on the unsteady flow field.

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.

Numerical investigation of the axial compressor performance with inlet distortions

2017 ◽  
Vol 232 (8) ◽  
pp. 1434-1441
Author(s):  
ZX Liu ◽  
HZ Diao ◽  
XC Zhu ◽  
ZH Du
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Body Force ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Force Model ◽  
Transonic Compressor ◽  
High Pressure Ratio ◽  
Compressor Performance

In this paper, a three-dimensional body force model for predicting compressor performance and stability is implemented in the Ansys CFX. The influence of the blade rows on the flow field is represented by the source terms of CFX-solver equation. At first, a high-speed and high-pressure-ratio transonic compressor with the clean inlet is investigated. The overall performance and the flow fields are in agreement well with those of the experimental date, so the model is reliable and correct. Then, the effects of the circumferential distortions in the inlet total pressure and the total temperature on the compressor performance and flow field are also illustrated, respectively. In summary, the proposed body force model is suitable to investigate the flow field of the compressor with the inlet distortions.

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
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