CFD Determination of Pre-Chamber Flow Pertubation Inlet Boundary Conditions for Seal Rotordynamics Models

2003 ◽  
Author(s):  
Ganesh Venkatesan ◽  
David L. Rhode
Keyword(s):  
Boundary Conditions ◽  
Operating Conditions ◽  
Test Cases ◽  
Computational Domain ◽  
New Approach ◽  
Flow Perturbation ◽  
Cfd Models ◽  
Approximate Boundary Conditions ◽  
Gas Seals

A new approach has been developed and utilized to determine the flow field perturbations (i.e. disturbances due to rotor whirl) upstream of a non-contacting seal. The results are proposed for use with bulk-flow perturbation and CFD-perturbation seal rotordynamic models, as well as with fully 3-D CFD models, to specify the approximate inlet boundary flow disturbance values at the computational domain inlet. The radially bulk-averaged disturbance quantities were evaluated in the upstream chamber from nearly 40 cases of geometry/operating conditions. The proposed upstream chamber boundary conditions are applicable for liquid as well as gas seals. For each of the measurement test cases considered, improved agreement with measurements was obtained when using the new boundary conditions, even though there was generally little room for improvement when not using the new boundary conditions. Based on the findings in this study it is recommended that the first-order correlations developed here be used to specify approximate boundary conditions at the domain inlet to be located in the upstream chamber.

The Validity of Approximate Boundary Conditions for Natural Convection With Thermal Radiation in Open Cavities

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Om Singh ◽  
Shireesh B. Kedare ◽  
Suneet Singh
Keyword(s):  
Natural Convection ◽  
Boundary Conditions ◽  
Significant Loss ◽  
Computational Effort ◽  
Computational Domain ◽  
Maximum Difference ◽  
Open Cavities ◽  
Shallow Cavities ◽  
Approximate Boundary Conditions ◽  
The Difference

Abstract The use of approximate boundary conditions at the opening of the cavities leads to restriction of the computational domain and, hence, the reduction in computational effort. However, the accuracy of the restricted domain approach (RDA) had been evaluated only for the natural convection inside open cavities and that too only for one aspect ratio (AR). The validity of the approach had not been evaluated for inclined, as well as, shallow cavities. This study focuses on the analysis of the accuracy of RDA against extended domain approach (EDA) in open cavities of different ARs, at different inclinations and different Rayleigh numbers (Ra). The results show that the difference between the approaches is only significant in very shallow cavities (AR is defined as the height of the hot wall divided by the depth of the cavity) at low Ra. For Ra higher than  106 and an AR greater than 0.2, the maximum difference between the two approaches is around 5% and hence RDA can be recommended in these ranges, resulting in increased computational efficiency without significant loss in the accuracy. Moreover, the maximum difference in the results for the two methods is for intermediate inclinations. Even there, an increase in the difference is more pronounced at lower Ra. Furthermore, distribution of the exit velocity and temperature at the opening as well as the distribution of the Nusselt number at the hot wall is compared for RDA and EDA to explain the behavior of error at different ARs and inclinations.

Allocating the Causes of Performance Deterioration in Combined Cycle Gas Turbine Plants

2002 ◽  
Vol 124 (2) ◽  
pp. 256-262 ◽  
Author(s):  
K. Mathioudakis ◽  
A. Stamatis ◽  
E. Bonataki
Keyword(s):  
Power Plant ◽  
Gas Turbine ◽  
Combined Cycle ◽  
Operating Conditions ◽  
Test Cases ◽  
Performance Deterioration ◽  
Baseline Values ◽  
The Way

A method for defining which parts of a combined cycle gas turbine (CCGT) power plant are responsible for performance deviations is presented. When the overall performances deviate from their baseline values, application of the method allows the determination of the component(s) of the plant, responsible for this deviation. It is shown that simple differentiation approaches may lead to erroneous conclusions, because they do not reveal the nature of deviations for individual components. Contributions of individual components are then assessed by separating deviations due to permanent changes and deviations due to change of operating conditions. A generalized formulation is presented together with the way of implementing it. Test cases are given, to make clearer the ideas put forward in the proposed method.

scholarly journals The Turbomachine Blading Design Achieved by Solving the Inverse Field Problem

1987 ◽  
Author(s):  
T. S. Luu ◽  
B. Viney
Keyword(s):  
Boundary Conditions ◽  
Stream Function ◽  
Design Procedure ◽  
Rotational Flow ◽  
Field Problem ◽  
New Approach ◽  
Vorticity Distribution ◽  
Function Formulation ◽  
Stream Function Formulation

This paper describes a design procedure for the determination of the geometry of the blading of the turbomachine with prescribed thickness and bound vorticity distribution. The boundary conditions are discussed in order to have a properly posed field problem. Optimised 2D cascade design example is shown. The quasi 3D “S2” - “S1” stream function formulation is developed. The design of guide vanes downstream of a lateral inlet casing is described. A new approach by introducing a potential like function to treat the 3D rotational flow is also formulated.

Disintegration of Oil Films Emerging From Radial Holes in a Rotating Cylinder

2001 ◽  
Author(s):  
A. Glahn ◽  
M. F. Blair ◽  
K. L. Allard ◽  
S. Busam ◽  
O. Schäfer ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Operating Conditions ◽  
Droplet Generation ◽  
Diameter Distribution ◽  
Oil Droplets ◽  
Flow Angle ◽  
Aero Engine ◽  
Oil Films ◽  
Engine Bearing

A fundamental study has been performed to examine the disintegration of oil films emerging from radial holes in a rotating hollow cylinder. The configuration investigated is an abstraction of one of the droplet generation sources in an aero-engine bearing compartment; similar configurations may also occur inside gearboxes. The paper aims to contribute to both the determination of directly applicable droplet characteristics and the establishment of a data-base that can be used for the development of droplet generation models. Similar to a prior paper on droplet generation processes at the rim of a rotating disk (Glahn et al, 2000), the near-term objectives of the study are (i) to determine droplet sizes under relevant aero-engine bearing compartment operating conditions, and (ii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced CFD-based design tools. Therefore, special emphasis has been directed towards a correlation of test results that enables determination of boundary conditions for a two-phase (oil droplets/air) simulation of lubrication system components. Based on the results of the present paper, droplet flow boundary conditions in terms of mean diameter, standard deviation of the diameter distribution, starting velocity, and flow angle are available for oil droplets generated by disintegration of oil films emerging from rotating radial holes and rotating disks.

A new approach to understanding and modelling the influence of wall roughness on friction factors for pipe and channel flows

2008 ◽  
Vol 613 ◽  
pp. 35-53 ◽  
Author(s):  
H. HERWIG ◽  
D. GLOSS ◽  
T. WENTERODT
Keyword(s):  
Turbulent Flows ◽  
Numerical Approach ◽  
Constant Factor ◽  
Laminar Flows ◽  
Test Cases ◽  
Wall Roughness ◽  
New Approach ◽  
Friction Factors ◽  
Dissipation Model

In this study, it is shown how the equivalent sand roughness required in the Moody chart can be calculated for arbitrarily shaped wall roughnesses. After a discussion of how to define the wall location and roughness height in the most reasonable way, a numerical approach based on the determination of entropy production in rough pipes and channels is presented. As test cases, three different two-dimensional roughness types have been chosen which are representative of regular roughnesses on machined surfaces. In the turbulent range, skin friction results with these test roughnesses can be linked to Nikuradse's sand roughness results by a constant factor. For laminar flows, a significant effect of wall roughness is identified which in most other studies is neglected completely. The dissipation model of this study is validated with experimental data for laminar and turbulent flows.

Disintegration of Oil Films Emerging From Radial Holes in a Rotating Cylinder

2003 ◽  
Vol 125 (4) ◽  
pp. 1011-1020 ◽  
Author(s):  
A. Glahn ◽  
M. F. Blair ◽  
K. L. Allard ◽  
S. Busam ◽  
O. Scha¨fer ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Droplet Diameter ◽  
Rotating Disk ◽  
Operating Conditions ◽  
Droplet Generation ◽  
Diameter Distribution ◽  
Oil Droplets ◽  
Flow Angle ◽  
Oil Films

A fundamental study has been performed to examine the disintegration of oil films emerging from radial holes in a rotating hollow cylinder. The configuration investigated is an abstraction of one of the droplet generation sources in an aeroengine bearing compartment; similar configurations may also occur inside gearboxes. The paper aims to contribute to both the determination of directly applicable droplet characteristics and the establishment of a database that can be used for the development of droplet generation models. Similar to a prior paper on droplet generation processes at the rim of a rotating disk (Glahn, A. et al., 2000, “Droplet Generation by Disintegration of Oil Films at the Rim of a Rotating Disk,” ASME Paper No. 2000-GT-0279.) the near-term objectives of the study are (i) to determine droplet sizes under relevant aeroengine bearing compartment operating conditions, and (ii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced CFD-based design tools. Therefore, special emphasis has been directed towards a correlation of test results that enables determination of boundary conditions for a two-phase (oil droplets/air) simulation of lubrication system components. Based on the results of the present paper, droplet flow boundary conditions in terms of mean diameter, standard deviation of the diameter distribution, starting velocity, and flow angle are available for oil droplets generated by disintegration of oil films emerging from rotating radial holes and rotating disks.

Quantitative Fourier-Domain Analysis. Part II: Determination of Boundary Conditions

1992 ◽  
Vol 46 (11) ◽  
pp. 1711-1718 ◽  
Author(s):  
Stephen L. Monfre ◽  
Steven D. Brown
Keyword(s):  
Boundary Conditions ◽  
Synthetic Data ◽  
Chemical System ◽  
Fourier Domain ◽  
Data Set ◽  
New Approach ◽  
Multicomponent Sample ◽  
Ft Ir ◽  
Ft Ir Spectroscopy

A new approach for determining the boundary conditions of a Fourier-domain data set prior to performing quantitative multicomponent analysis has been developed. Processing boundary conditions were determined by calculating the condition number of the calibration matrix which contains the models used to describe the chemical system being studied. Once the boundary conditions for the Fourier-domain data set were determined, the Kalman filter was used to estimate the concentration of individual components in a multicomponent sample. Synthetic data were first analyzed to determine both the feasibility of the data-analysis method and the effect that background variations would have on the concentration estimates. Raw interferograms of multicomponent samples, collected with the use of Fourier transform infrared (FT-IR) spectroscopy, were also analyzed. Validation samples were analyzed to verify the chosen boundary conditions.

Simulation and Contrast Analysis of tem Images of Cracks

1990 ◽  
Vol 48 (1) ◽  
pp. 578-579
Author(s):  
D. Goyal ◽  
A. H. King
Keyword(s):  
Displacement Vector ◽  
Crack Tip ◽  
Perfect Crystal ◽  
Operating Conditions ◽  
Displacement Fields ◽  
Fringe Contrast ◽  
Orthogonal Geometry ◽  
Moire Fringe ◽  
Moiré Fringe

TEM images of cracks have been found to give rise to a moiré fringe type of contrast. It is apparent that the moire fringe contrast is observed because of the presence of a fault in a perfect crystal, and is characteristic of the fault geometry and the diffracting conditions in the TEM. Various studies have reported that the moire fringe contrast observed due to the presence of a crack in an otherwise perfect crystal is distinctive of the mode of crack. This paper describes a technique to study the geometry and mode of the cracks by comparing the images they produce in the TEM because of the effect that their displacement fields have on the diffraction of electrons by the crystal (containing a crack) with the corresponding theoretical images. In order to formulate a means of matching experimental images with theoretical ones, displacement fields of dislocations present (if any) in the vicinity of the crack are not considered, only the effect of the displacement field of the crack is considered.The theoretical images are obtained using a computer program based on the two beam approximation of the dynamical theory of diffraction contrast for an imperfect crystal. The procedures for the determination of the various parameters involved in these computations have been well documented. There are three basic modes of crack. Preliminary studies were carried out considering the simplest form of crack geometries, i. e., mode I, II, III and the mixed modes, with orthogonal crack geometries. It was found that the contrast obtained from each mode is very distinct. The effect of variation of operating conditions such as diffracting vector (), the deviation parameter (ω), the electron beam direction () and the displacement vector were studied. It has been found that any small change in the above parameters can result in a drastic change in the contrast. The most important parameter for the matching of the theoretical and the experimental images was found to be the determination of the geometry of the crack under consideration. In order to be able to simulate the crack image shown in Figure 1, the crack geometry was modified from a orthogonal geometry to one with a crack tip inclined to the original crack front. The variation in the crack tip direction resulted in the variation of the displacement vector also. Figure 1 is a cross-sectional micrograph of a silicon wafer with a chromium film on top, showing a crack in the silicon.

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