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Featured researches published by Aarthi Sekaran.


Journal of Fluids Engineering-transactions of The Asme | 2016

An Inquiry of the Friction Factor “Jump” Phenomenon in Hole-Pattern Seals

Aarthi Sekaran; Gerald L. Morrison; Devesh Ranjan

Experiments measuring the leakage rate through hole-pattern seals operating at high pressures of up to 8400 kPa reveal the presence of an abrupt variation in the friction factor (up to a factor of three) with change in the pressure difference across the seal. The measured pressure fluctuations suggest that this observation may, perhaps, be understood as a change in fluid instability modes across the cavities of the seal. A more detailed investigation via large eddy simulations (LES) suggest that the switching from shear layer instability mode to a wake instability mode, a phenomenon well known in fundamental studies of cavity flow (without a top bounding wall), is responsible for the observed variation.


Volume 1B, Symposia: Fluid Machinery; Fluid Power; Fluid-Structure Interaction and Flow-Induced Noise in Industrial Applications; Flow Applications in Aerospace; Flow Manipulation and Active Control: Theory, Experiments and Implementation; Fundamental Issues and Perspectives in Fluid Mechanics | 2013

Effects of Adding a Central Groove to the Squeeze Film Damper Lands

Praneetha Boppa; Aarthi Sekaran; Gerald L. Morrison

Squeeze film dampers (SFDs) are used in the high speed turbo machinery industry and aerospace industry as a means to reduce vibration amplitude, to provide damping, to improve dynamic stability of the rotor bearing system and to isolate structural components. Past studies have not included effects of variation of the stator geometries in a squeeze film damper. A central groove added to the squeeze film land is hypothesized to provide a uniform flow source which theory predicts will result in forces less than one fourth of that seen in SFDs without a central groove. In the present study, 3D numerical simulations of SFDs with different size central grooves on the squeeze film land are performed to predict the variation of the dynamic pressure profiles. The numerical model and method have been validated via comparison to experimental data for a SFD without a central groove. When a central groove is added to the squeeze film land, the pressures generated are reduced to half of that generated when run without a central groove on the land. The amount of reduction in pressure values depends on the volume of the groove, not on the aspect ratio of the groove. Addition of a central groove reduces the pressures, rigidity developed in squeeze film land, and forces generated by squeeze film damper.Copyright


Volume 1B, Symposia: Fluid Machinery; Fluid Power; Fluid-Structure Interaction and Flow-Induced Noise in Industrial Applications; Flow Applications in Aerospace; Flow Manipulation and Active Control: Theory, Experiments and Implementation; Fundamental Issues and Perspectives in Fluid Mechanics | 2013

Analysis of the ‘Friction Factor Jump’ Phenomenon in Hole-Pattern Seals

Aarthi Sekaran; Gerald L. Morrison

Hole-pattern and honeycomb seals are used to replace labyrinth seals in turbomachinery that are experiencing vibration problems, such as high pressure gas compressors. Computer simulations used to investigate the stability of a rotordynamic system require information about the stiffness, damping, and added mass generated by bearings and seals. These codes typically use bulk flow models for the fluid flow inside the bearings and seals which require empirical information about how the friction factor and leakage rate vary with rotor speed and pressure drop across the seal. Historically, experimental facilities were constructed to provide empirical data which were then used in the rotordynamic models. Ha et al (1992) observed a sudden change in the flow rate and resulting friction factor in a honeycomb seal as the pressure differential across the seal increased. This ‘friction factor jump’ was attributed to the shear flow over a seal cavity changing from a dominant normal mode to a dominant feedback mode. This was confirmed through pressure spectra showing that indeed, the shear layer instability mode changed and the frequencies present compared to predicted values. A similar effect has recently been observed in hole-pattern seals operating at high pressures, 84 bar (1200 psi). However, the pressure fluctuation spectra did not confirm the same mode change observed by Ha. The friction factor changed a by factor of around three in this instance which can drastically change the stability of the rotating system. This high pressure flow has a higher Reynolds number due to the high pressures which may explain the difference. An experimental investigation has confirmed the presence of the “friction factor jump” and that there is a change in the pressure fluctuation spectra. Further experimental investigation coupled with Large Eddy Simulation (LES) of the flow field have confirmed there is a change in the shear layer over the cavity but not the same as observed by Ha. Comparisons between the experimental and computational results are made along with an explanation of the flow phenomena.Copyright


ASME Turbo Expo 2013: Turbine Technical Conference and Exposition | 2013

A Numerical Study of Squeeze Film Dampers

Praneetha Boppa; Gerald L. Morrison; Aarthi Sekaran

Squeeze film dampers (SFDs) are used in the high speed turbomachinery industry as a means to reduce vibration amplitude, provide damping, and improve dynamic stability of the rotor bearing system. Past numerical studies analyzing SFDs, have been computationally expensive and time consuming. The present study investigates the feasibility of applying a steady state solver to obtain computational efficiency while ensuring that the parameters of interest are captured. This is done via the application of the Moving Reference Frame (MRF) solver in ANSYS® Fluent. A steady state solver in an absolute frame of reference was used to produce whirling motion of the rotor. The results are validated by comparison to the experimental data of Delgado [1]. The numerical model shows good agreement with these results.Copyright


ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels | 2010

Study of the Impact of Change of Clearance on the Flow Field and Rotordynamic Coefficients for a Smooth, Whirling Annular Seal

Aarthi Sekaran; Gerald L. Morrison

The flow field and the rotordynamic coefficients for a smooth, whirling annular seal were investigated by means of a CFD study involving a full 3D model. The preliminary model (of clearance 1.27mm) was validated by comparison to existing experimental flow field data after which CFD simulations were made for a smaller clearance (0.127mm). The flow field changed significantly with the change in clearance and it was seen that the larger clearance showed an inertia dominated flow regime as opposed to the viscous flow regime for the small clearance. Upon the implementation of Childs’ theory for the computation of rotordynamic coefficients, it was observed that forces for the larger clearance did not exhibit the whirl ratio dependence assumed in this theory. The smaller clearance however showed the expected trend with values of the coefficients in the range predicted.Copyright


Bulletin of the American Physical Society | 2016

Large eddy simulations of the flow field of a radially lobed nozzle

Noushin Amini; Aarthi Sekaran


Bulletin of the American Physical Society | 2015

Large Eddy Simulations and an Analysis of the Flow Field of a Radially Lobed Nozzle

Noushin Amini; Aarthi Sekaran


Bulletin of the American Physical Society | 2014

A bursting phenomenon in a vortex-gas boundary layer

Aarthi Sekaran; R. Narasimha; Rama Govindarajan


Bulletin of the American Physical Society | 2014

Numerical simulation of the flow field from a radially lobed nozzle and validation via HWA

Noushin Amini; Aarthi Sekaran


The International journal of mechanical engineering education | 2012

An Experimental Investigation of the Free Jet Flow from a Radially Lobed Nozzle Using Hot-Wire Anemometry

Noushin Amini; Aarthi Sekaran; Markus Schwaenen; Anand Vijaykumar; Devesh Ranjan

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Devesh Ranjan

Georgia Institute of Technology

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R. Narasimha

Jawaharlal Nehru Centre for Advanced Scientific Research

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Rama Govindarajan

Jawaharlal Nehru Centre for Advanced Scientific Research

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