Numerical Investigations on Rotordynamic Characteristic of Hole-Pattern Seals With Two Different Hole-Diameters

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Xin Yan ◽  
Kun He ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Total Energy ◽  
Constant Temperature ◽  
Turbulence Model ◽  
Ideal Gas ◽  
Hole Diameter ◽  
Bulk Flow ◽  
Numerical Accuracy ◽  
Flow Method ◽  
Rotordynamic Coefficients ◽  
Diameter Hole

The rotordynamic characteristic of the hole-pattern seals with two different hole-diameters was investigated using the unsteady Reynolds-averaged Navier–Stokes (URANS) equations solutions and bulk flow methods. The mesh deformation method combined with elliptical orbit model was adopted to numerically solve the transient flow fields. By integrating the transient reaction forces on the rotor surface, the rotordynamic coefficients of the hole-pattern seals at a set of excitation frequencies were obtained with the reaction-force/motion model. The effects of mesh density, constant temperature assumption, and turbulence model on the numerical accuracy were analyzed for both large hole-diameter hole-pattern (LDHP) and small hole-diameter hole-pattern (SDHP) seals. The comparisons between the two bulk flow methods (i.e., the isothermal bulk flow method (ISOTSEAL) and the ideal gas bulk flow method with energy equation (ideal gas bulk flow model)) and transient computational fluid dynamics (CFD) method were performed. It shows that, compared to the experimental data, the isothermal URANS (constant temperature assumption) and total energy URANS (consider the temperature varying) solutions almost have the same accuracy with respect to the rotordynamic coefficients predictions. However, for the direct damping coefficient predictions, the total energy URANS method has a slight advantage over the isothermal URANS for both SDHP and LDHP cases. For the LDHP seal, the predicted rotordynamic coefficients are not sensitive to the selected turbulence models, but as the hole-diameter becomes smaller, the effect of turbulence model on the numerical accuracy becomes pronounced. Among the studied numerical methods, the isothermal URANS solutions with standard k–ε turbulence model have a good performance taking both numerical accuracy and computational time into consideration. For the SDHP seal, the present ideal gas bulk flow method and ISOTSEAL can provide the reasonable predictions of the rotordynamic coefficients. However, for the LDHP seal, both of them show a low accuracy in predicting the rotordynamic coefficients.

A Numerical Study on the Influence of Hole Depth on the Static and Dynamic Performance of Hole-Pattern Seals

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Patrick J. Migliorini ◽  
Alexandrina Untaroiu ◽  
Houston G. Wood
Keyword(s):  
Steady State ◽  
Turbulence Model ◽  
Gas Turbines ◽  
Numerical Study ◽  
Bulk Flow ◽  
Hole Depth ◽  
Rotordynamic Coefficients ◽  
The Impact ◽  
Good Agreement ◽  
Annular Seals

Annular seals serve an important role in the dynamics of turbomachinery by reducing leakage of a process fluid while also contributing potentially destabilizing forces to the rotor system. Hole-pattern seals have been the focus of many investigations, but recent experimental studies have shown that there are still many phenomena that require exploration. One such phenomenon is the influence of hole depth on the static and dynamic characteristics of the seal. In this paper, a hybrid computational fluid dynamics (CFD)/bulk-flow method is employed to investigate the nonmonotonic relationship between hole depth and leakage shown in experimental measurements of a hole-pattern seal by Childs et al. (2014, “The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals,” ASME J. Eng. Gas Turbines Power, 136(4), p. 042501). Three hole depths (1.905 mm, 3.302 mm, and 6.604 mm) and three running speeds (10,200 rpm, 15,350 rpm, and 20,200 rpm) are considered. For the steady-state flow, the 3D Reynolds-Averaged-Navier-Stokes (RANS) equations are solved with the k-ϵ turbulence model for a circumferentially periodic sector of the full seal geometry. The steady-state results are input into the first-order equations of a bulk-flow model to predict rotordynamic coefficients. Results of the hybrid method are compared to experimental data. CFD predicted leakage showed good agreement (within 5%) for the 3.302 mm and 6.604 mm hole depth configurations. For the 1.905 mm hole depth seal, agreement was within 17%. An additional set of calculations performed with the shear stress transport (SST) turbulence model produced worse agreement. Examination of streamlines along the seal show that the hole depth controls the shape of the vortex that forms in the hole, driving the resistance experienced by the jet flow in the clearance region. For the rotordynamic coefficients, good agreement is shown between predictions and experiment for most excitation frequencies.

Numerical Modeling of Fluid-Induced Rotordynamic Forces in Seals With Large Aspect Ratio

2012 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Costin D. Untaroiu ◽  
Houston G. Wood ◽  
Paul E. Allaire
Keyword(s):  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Difference Method ◽  
Dynamic Properties ◽  
Bulk Flow ◽  
Large Aspect Ratio ◽  
Flow Method ◽  
Dynamic Coefficients ◽  
Aspect Ratios

Traditional annular seal models are based on bulk flow theory. While these methods are computationally efficient and can predict dynamic properties fairly well for short seals, they lack accuracy in cases of seals with complex geometry or with large aspect ratios (above 1.0). In this paper, the linearized rotordynamic coefficients for a seal with large aspect ratio are calculated by means of a three dimensional CFD analysis performed to predict the fluid-induced forces acting on the rotor. For comparison, the dynamic coefficients were also calculated using two other codes: one developed on the bulk flow method and one based on finite difference method. These two sets of dynamic coefficients were compared with those obtained from CFD. Results show a reasonable correlation for the direct stiffness estimates, with largest value predicted by CFD. In terms of cross-coupled stiffness, which is known to be directly related to cross-coupled forces that contribute to rotor instability, the CFD predicts also the highest value; however a much larger discrepancy can be observed for this term (73% higher than value predicted by finite difference method and 79% higher than bulk flow code prediction). Similar large differences in predictions one can see in the estimates for damping and direct mass coefficients, where highest values are predicted by the bulk flow method. These large variations in damping and mass coefficients, and most importantly the large difference in the cross-coupled stiffness predictions, may be attributed to the large difference in seal geometry (i.e. the large aspect ratio AR>1.0 of this seal model vs. the short seal configuration the bulk flow code is usually calibrated for, using an empirical friction factor).

A Study of a Sharp 90 Degree Curved Flow

1992 ◽  
Author(s):  
R. H. Kim
Keyword(s):  
Turbulence Model ◽  
Ideal Gas ◽  
Radius Of Curvature ◽  
Dimensional Theory ◽  
One Dimensional ◽  
Algebraic Stress Model ◽  
Finite Difference Technique ◽  
Curved Tube ◽  
Kinetic Energy Loss ◽  
The Ideal

Abstract An investigation of air flow along a 90 degree elbow-like tube is conducted to determine the velocity and temperature distributions of the flow. The tube has a sharp 90 degree turn with a radius of curvature of almost zero. The flow is assumed to be a steady two-dimensional turbulent flow satisfying the ideal gas relation. The flow will be analyzed using a finite difference technique with the K-ε turbulence model, and the algebraic stress model (ASM). The FLUENT code was used to determine the parameter distributions in the passage. There are certain conditions for which the K-ε model does not describe the fluid phenomenon properly. For these conditions, an alternative turbulence model, the ASM with or without QUICK was employed. FLUENT has these models among its features. The results are compared with the result computed by using elementary one-dimensional theory including the kinetic energy loss along the passage of the sharp 90 degree curved tube.

A Comparison of Rotordynamic-Coefficient Predictions for Annular Honeycomb Gas Seals Using Three Different Friction-Factor Models

2002 ◽  
Vol 124 (3) ◽  
pp. 524-529 ◽  
Author(s):  
Rohan J. D’Souza ◽  
Dara W. Childs
Keyword(s):  
Friction Factor ◽  
Flow Model ◽  
Factor Model ◽  
Control Volume ◽  
Bulk Flow ◽  
Shear Stresses ◽  
Steam Turbines ◽  
Frequency Range ◽  
Rotordynamic Coefficients ◽  
Rotordynamic Coefficient

A two-control-volume bulk-flow model is used to predict rotordynamic coefficients for an annular, honeycomb-stator/smooth-rotor gas seal. The bulk-flow model uses Hirs’ turbulent-lubrication model, which requires a friction factor model to define the shear stresses at the rotor and stator wall. Rotordynamic coefficients predictions are compared for the following three variations of the Blasius pipe-friction model: (i) a basic model where the Reynolds number is a linear function of the local clearance, fs=ns Rems (ii) a model where the coefficient is a function of the local clearance, and (iii) a model where both the coefficient and exponent are functions of the local clearance. The latter models are based on data that shows the friction factor increasing with increasing clearances. Rotordynamic-coefficient predictions shows that the friction-factor-model choice is important in predicting the effective-damping coefficients at a lower frequency range (60∼70 Hz) where industrial centrifugal compressors and steam turbines tend to become unstable. At a higher frequency range, irrespective of the friction-factor model, the rotordynamic-coefficient predictions tend to coincide. Blasius-based Models which directly account for the observed increase in stator friction factors with increasing clearance predict significantly lower values for the destabilizing cross-coupled stiffness coefficients.

Rotordynamic Characteristics of the Straight-Through Labyrinth Seal Based On the Applicability Analysis of Leakage Models Using Bulk-Flow Method

2021 ◽  
Author(s):  
Tianhao Wang ◽  
Zhigang Li ◽  
Jun Li
Keyword(s):  
Rotational Speed ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Inlet Pressure ◽  
Leakage Flow ◽  
Flow Method ◽  
Leakage Model ◽  
Outlet Pressure ◽  
Prediction Approach

Abstract Labyrinth seals are widely applied in the turbomachinery to control the leakage flow through the clearance between the stationary and rotating components. The fluid excitation induced by the labyrinth seal would deteriorate the stability of turbomachinery shaft. Developing an accurate and rapid prediction approach is crucial for the analysis of the fluid excitation rotordynamics of the labyrinth seal. The objective of this study is to analyze the applicability of leakage models using Bulk-Flow method and investigate the factors affecting the rotordynamic characteristics of the labyrinth seal. An elliptical orbit for rotor whirling was assumed in the one-control-volume Bulk-Flow model considering an isentropic process to predict the frequency-dependent rotordynamic coefficients of the labyrinth seal. The optimal leakage model was determined by comprehensively analyzing the applicability of 72 leakage models. Employing the optimal leakage model in the Bulk-Flow method, the effects of sealing clearance, pressure ratio, preswirl ratio and rotational speed on the rotordynamic characteristics of the labyrinth seal were investigated. The conclusions show that the Bulk-Flow method has an average prediction error of around 10% for the leakage flow rate, cross-coupled stiffness and direct damping when equipped with the optimal leakage model. Increasing preswirl ratio has a significantly destabilizing effect on the rotor stability, while the influence of increasing rotational speed is strongly related to preswirl direction. The effective damping of the labyrinth seal is sensitive to the inlet pressure, but insensitive to the outlet pressure and sealing clearance. The crossover frequency is almost impervious to the inlet pressure, outlet pressure and sealing clearance.

Application of TOPSIS Method for Prediction of Optimum Design Parameters of Micro Hole Textured Cutting Inserts in Turning of Al-MMC

2021 ◽  
Vol 13 (4) ◽  
Author(s):  
S. Devaraj ◽  
M. Ramakrishna ◽  
B. Singaravel
Keyword(s):  
Optimum Design ◽  
Hole Diameter ◽  
Machining Process ◽  
Cutting Fluid ◽  
Design Parameters ◽  
Topsis Method ◽  
Hole Depth ◽  
Diameter Hole ◽  
Relative Closeness ◽  
Micro Hole

Metal Matrix Composite (MMC) has better mechanical properties and it is possible to produce near net shape. Aluminum-based MMC (Al-MMC) has challenges in terms of machinability studies and estimation of its optimum process parameters. Alternative cutting fluid research is a challenging area in machining. To avoid, existing hydrocarbon oil-based cutting fluid, textured inserts embedded with a solid lubricant are one of the alternative solutions. Micro hole textured inserts make a hole on the rake face of the cutting tool inserts. Texture includes various important design parameters namely hole diameter, hole depth and pitch between the holes. These optimum parameters influence the machining process. In this work, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method is used to find the optimum design parameters (hole diameter, hole depth and pitch between holes) during turning of Al- MMC. The objective parameters considered are minimization of surface roughness, power consumption and tool flank wear. The optimum combination of these design parameters is obtained by the higher relative closeness value of the TOPSIS method. The result of the investigation revealed that these design parameters are important to obtain improved machining performance. Also, it is understood that the TOPSIS method has an appropriate procedure to solve multiple objective optimization problems in manufacturing industries.

Numerical Simulation of Flows through Labyrinth Seals

2016 ◽  
Vol 821 ◽  
pp. 16-22 ◽  
Author(s):  
Jiří Fürst
Keyword(s):  
Numerical Simulation ◽  
Numerical Solution ◽  
Finite Volume ◽  
Stokes Equations ◽  
Control Volume ◽  
Experimental Results ◽  
Numerical Code ◽  
Labyrinth Seals ◽  
Flow Method ◽  
Rotordynamic Coefficients

A numerical code for calculation of leakage flowand rotordynamic coefficients of labyrinth seals has beendeveloped. The code is based on the solution of Reynolds-averagedNavier-Stokes equations combined with a two-equation turbulencemodel. The numerical solution is achieved with finite volume methodand the rotordynamic coefficients are evaluated from severalsimulations with different rotor precessions. The solution iscompared to single control volume based bulk flow method[Williams, 1998] and to the experimental results for look-throughlabyrinth seal [Schettel, 2004].

Experimental Measurement of a Three Lobe Air Bearing Rotordynamic Coefficients

2006 ◽  
Author(s):  
Rafael O. Ruiz ◽  
Marcelo H. Di Liscia ◽  
Sergio Di´az ◽  
Luis Medina
Keyword(s):  
Reynolds Equation ◽  
Ideal Gas ◽  
Magnetic Bearing ◽  
Experimental Results ◽  
Rotating Speed ◽  
Rotordynamic Coefficients ◽  
Fluid Film Bearings ◽  
Bearing Force ◽  
Air Film ◽  
Gas Journal Bearing

This work presents direct experimental measurements of air film rotordynamic coefficients on a three lobe bearing. The test rig uses two magnetic bearing actuators to impose desired test orbits to the journal. Tests are conducted at several rotating speeds up to 12,000rpm. Journal whirling excitation is independent of the rotating speed, thus allowing asynchronous excitations. One-dimensional orbits in the horizontal and vertical axes are applied as excitations at each rotating speed. The experimental results show the behavior of the rotordynamic coefficients of the air film bearing under synchronous and asynchronous excitation. The synchronous experimental results are compared to numerical estimation of the bearing force coefficients through solution of the isotropic ideal gas journal bearing Reynolds equation coupled with the pressure drop through the feeding holes. The results of this work prove the suitability of the rig to identify both the synchronous and nonsynchronous response of air fluid film bearings.

scholarly journals PENENTUAN JUMLAH MOL UDARA DALAM SELINDER DAN BOLA MENGGUNAKAN HUKUM BOYLE-MARIOTTE

2013 ◽  
Vol 5 (1) ◽  
pp. 41-45
Author(s):  
MATHEUS SOUISA
Keyword(s):  
Constant Temperature ◽  
Ideal Gas ◽  
Constant Volume ◽  
Ideal Gas Law ◽  
The Ideal

Has done research on different container and the syringe bulb to determine the number of moles of air. If the gas or air is introduced into the syringe or bulb then the more air is forced into it. The analysis uses Boyle-Mariotte law shows that the number of moles of air in the syringe with constant temperature and number of moles of air at constant volume is a sphere with eqqual 0.02 mol. Thus two different media (cylindrical and spherical), giving the same number of moles. Obtaining the number of moles show that the application of Boyle-Mariotte is derived from the ideal gas law is appropriate.

A Novel Bulk-Flow Model for Pocket Damper Seals

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Filippo Cangioli ◽  
Giuseppe Vannini ◽  
Thomas Chirathadam
Keyword(s):  
Flow Model ◽  
Control Volume ◽  
Dynamic Pressure ◽  
Bulk Flow ◽  
Order System ◽  
Shear Stresses ◽  
Flow Area ◽  
Rotordynamic Coefficients ◽  
Recirculating Flow ◽  
Numerical Predictions

Abstract In this paper, a novel bulk-flow model for pocket damper seals (PDS) is introduced. The model is based on two control volumes (CVs) for each circumferential pocket of the seal. The continuity, circumferential momentum, and energy equations are considered for each control volume. The circumferential recirculating flow within the pocket is modeled for the first time. The boundary layer theory is used to estimate the recirculating flow area, and the Swamee–Jain friction factor correlation allows for defining the dissipation of the circumferential velocity. The perturbation method is used to solve the partial derivative governing equations in the zeroth- and first-order system of equations. The rotordynamic coefficients are evaluated by integrating the dynamic pressure and rotor shear stresses along the circumferential direction. The predictions are compared to the experimental data, which refer to test conditions representative of high-pressure centrifugal compressors. Numerical predictions are accurate for both high positive–negative inlet preswirl ratios. Leakage predictions are also aligned with measurements. Finally, sealing selection approach is introduced in the paper for comparing the dynamic behavior of two different sealing technologies and identifying stable regions as a function of the rotor natural frequency and preswirl ratio.

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