Papers by Chelakara Subramanian
Florida Tech's Wireless Sensor Network (WSN) system consists of pressure and temperature sensors,... more Florida Tech's Wireless Sensor Network (WSN) system consists of pressure and temperature sensors, and anemometer. The objective of the WSN is to collect data to measure wind loads on a variety of components on residential houses, such as roof, walls, windows, fascia, soffits, and shingles. The WSN system is generally deployed in the field on residential houses during tropical storms or hurricanes, while in laboratory tests the WSN system is deployed on a full-or largescale model house in the Wall of Wind (WoW) at Florida International University (FIU). The WSN system collects data and communicates wirelessly to a local laptop. The system has the capability to upload the collected data in quasi-realtime to a cloud data storage by public Wi-Fi. This article describes how to synchronize the WSN system operations with the NSF-NHERI (National Science Foundation-Natural Hazards Engineering Research Infrastructure) cloud platform DesignSafe-CI for data uploading, processing, analysis, and visualization.
Discussion is printed only if the paper is published in an ASME Journal. Papers are available
P. M. Ligrani Effects of Vortices With Different Circulations on Heat Transfer and Injectant Downstream of a Single Film-Cooling Hole in a Turbulent Boundary Layer
Results are presented that illustrate the effects of single embedded longitudinal vortices on hea... more Results are presented that illustrate the effects of single embedded longitudinal vortices on heat transfer and injectant downstream of a single film-cooling hole in
Velocity and Temperature Fluctuation Measurements in a Turbulent Boundary Layer Downstream of u Stepwise Discontinuity in Wall Temperature
Acknowledgments The experimental data were obtained at the University
AIAA 2000-2526 INTENSITY BIASED PSP MEASUREMENT C. S. Subramanian Florida Institute of Technology, Melbourne, FL
The current pressure sensitive paint (PSP) technique assumes a linear relationship (Stern-Voimer ... more The current pressure sensitive paint (PSP) technique assumes a linear relationship (Stern-Voimer Equation) between intensity ratio (Io/I) and pressure ratio (P/Po) over a wide range of pressures (vacuum to ambient or higher). Although this may be valid for some PSPs, in most PSPs the relationship is nonlinear, particularly at low pressures (<0.2 psia when the oxygen level is low). This non-linearity can be attributed to variations in the oxygen quenching (de-activation) rates (which otherwise is assumed constant) at these pressures. Other studies suggest that some paints also have non-linear calibrations at high pressures; because of heterogeneous (non-uniform) oxygen diffusion and quenching. Moreover, pressure sensitive paints require correction for the output intensity due to light intensity variation, paint coating variation, model dynamics, wind-off reference pressure variation, and temperature sensitivity. Therefore to minimize the measurement uncertainties due to these caus...
Measurements of the low-wave-number structure of a turbulent boundary layer
Advances in Fluid Mechanics VI
Nikuradse uses the equivalent sand-grain roughness to characterize the effect of roughness. While... more Nikuradse uses the equivalent sand-grain roughness to characterize the effect of roughness. While this approach works when the roughness is contained in the inner layer, it does not apply in recent studies with a larger roughness. Various techniques have been applied in the past to scale the mean velocity and the Reynolds stress profiles for a zero pressure gradient boundary layer, the classical scaling using the friction velocity u* to normalize the velocity profiles. However none of these techniques holds universally. This study attempts to improve the understanding that we have of the way roughness affects the inner layer behaviour and aims to find an alternative scaling parameter for cases where roughness is large compared to the inner layer. Measured mean and turbulent velocity profiles on a large regular roughness show a non-zero wall normal pressure is caused which contributes to the velocity deficit in the near wall rough boundary layer velocity profile. The normal turbulent stresses are also increased. Hence a pressure gradient velocity rather than the friction velocity is defined to capture the pressure effects induced by roughness. The power law seems to give a better representation of the velocity profiles than the log law in this case.
Advances in Fluid Mechanics VI, Apr 19, 2006
Nikuradse uses the equivalent sand-grain roughness to characterize the effect of roughness. While... more Nikuradse uses the equivalent sand-grain roughness to characterize the effect of roughness. While this approach works when the roughness is contained in the inner layer, it does not apply in recent studies with a larger roughness. Various techniques have been applied in the past to scale the mean velocity and the Reynolds stress profiles for a zero pressure gradient boundary layer, the classical scaling using the friction velocity u* to normalize the velocity profiles. However none of these techniques holds universally. This study attempts to improve the understanding that we have of the way roughness affects the inner layer behaviour and aims to find an alternative scaling parameter for cases where roughness is large compared to the inner layer. Measured mean and turbulent velocity profiles on a large regular roughness show a non-zero wall normal pressure is caused which contributes to the velocity deficit in the near wall rough boundary layer velocity profile. The normal turbulent stresses are also increased. Hence a pressure gradient velocity rather than the friction velocity is defined to capture the pressure effects induced by roughness. The power law seems to give a better representation of the velocity profiles than the log law in this case.
Noncontact Measurement of Marine Biofouling Roughness
Marine Technology and SNAME News
The energy loss caused by biofouling is costing the marine operations millions of dollars because... more The energy loss caused by biofouling is costing the marine operations millions of dollars because of lack of complete understanding of their roughness characteristics. Marine biofouling roughness is generally randomly distributed in space, and also varies in shape and texture. The common practice in hydrodynamic analysis is to ignore the details and express them simply by means of a representative length scale dimension. However, many recent studies have shown that this is not a satisfactory approach, particularly when the roughness height is large. The present research aims to develop a better measure of biofouling roughness by using an innovative image analysis technique to model and predict the related hydrodynamic phenomena. The proposed technique employs a combination of stochastic and triangulation techniques that are commonly used in image analysis. An overview of these techniques for surface topography measurement is provided. The present method uses two images of the surfac...
A Wireless Sensors Network System for Local Multipoint Storm Surge Measurements
Marine Technology Society Journal
Proceedings of the 3rd International Conference of Fluid Flow, Heat and Mass Transfer (FFHMT'16), 2016
This research focuses on understanding the drag of thin flexible wires in a cross flow at low lam... more This research focuses on understanding the drag of thin flexible wires in a cross flow at low laminar Reynolds numbers. Experiments are conducted to measure the drag force for thin flexible wire of O(mm) at Reynolds number, based on wire diameter, range between 250 to 1000 and, the results showed 20% to 30 % of reduction in the drag coefficient as compared to previous quoted results in the open literature. The direct numerical simulation study is carried out for the similar flow (but for a less flexible wire) using the commercial CFD code ANSYS Fluent 15.0 and with mesh generation ANSYS ICEM-CFD 15.0 software. The computational results confirmed the experimental results. To further explain the fluid dynamic mechanism causing the drag reduction in this range of Reynolds numbers, wake surveys are performed using pitot static tube and hot wire experiments as well as time resolved computational numerical simulations. The near wake flow structure suggests the wake transition may be the cause of reduced drag, similar to the drag crisis commonly observed in the wire boundary layer transition regime.
Structure of turbulence in three-dimensional boundary layers
Final Technical Report Florida Inst of Tech Melbourne Dept of Mechanical and Aerospace Engineering, Feb 1, 1993
This report provides an overview of the three dimensional turbulent boundary layer concepts and o... more This report provides an overview of the three dimensional turbulent boundary layer concepts and of the currently available experimental information for their turbulence modeling. It is found that more reliable turbulence data, especially of the Reynolds stress transport terms, is needed to improve the existing modeling capabilities. An experiment is proposed to study the three dimensional boundary layer formed by
Boundary Layer Characteristics with Large K-type Roughness
A rough surface with a large (3 mm width x 6 mm height)k-type roughness was introduced into a fla... more A rough surface with a large (3 mm width x 6 mm height)k-type roughness was introduced into a flat-plate boundary layer flow to study their interaction. Pitot tube, pitot-static tube, Preston tube, normal hot wire, crossed- hot wire and visualization techniques were employed to obtain the mean and fluctuating flow field, as well as the surface friction characteristics. The Reynolds
Device and method for measuring thermal conductivity of thin films
Scaling Law For Turbulent Boundary Layer With Strong Irregular Roughness
Surface roughness causes large drag penalties in many applications. For all naturally occurring r... more Surface roughness causes large drag penalties in many applications. For all naturally occurring roughness, Nikuradse suggested a method of determining the equivalent uniform sand-grain roughness, which became a standard means to characterize their effects on flow behavior. The inner layer laws are based on this equivalent sand-grain roughness scale. While this approach works in cases where the roughness is contained
Scaling Law For Turbulent Boundary Layer With Strong Irregular Roughness
Surface roughness causes large drag penalties in many applications. For all naturally occurring r... more Surface roughness causes large drag penalties in many applications. For all naturally occurring roughness, Nikuradse suggested a method of determining the equivalent uniform sand-grain roughness, which became a standard means to characterize their effects on flow behavior. The inner layer laws are based on this equivalent sand-grain roughness scale. While this approach works in cases where the roughness is contained
A Study of Hydrodynamic Characteristics of Boundary Layer With Algae Roughness
Volume 1: Fora, Parts A and B, 2002
Filamentous algae fouling, such as Enteromorpha clathrata, is a soft and hairylike roughness that... more Filamentous algae fouling, such as Enteromorpha clathrata, is a soft and hairylike roughness that sometimes grows even thicker than a normal boundary layer. Typically, such fouling has been treated as traditional roughness functions to yield hydrodynamic characteristics. This technique has been successfully used for a thin fouling layer. However, it may not be applicable on a thicker layer, as the present study found substantial fluid flow within the layer. For such cases, the roughness cannot be treated simply as a passive geometric variable, but its kinematics and interactions with the flow must be considered. The inner law (log law) dynamics may be abnormal to yield any meaningful roughness function if it is calculated in the traditional way as the departure of a rough-wall log law profile over a smooth-wall log law profile. In the present research, velocity measurement of the E. clathrata roughness boundary layer using pitot-static tube and laser Doppler velocimeter (LDV) were compared. Large discrepancies in the velocity profiles within and in the vicinity of the roughness layer were observed between the two methods. The pitot-static tube data showed significantly high velocities (60% to 80% of the free stream) in the inner layer as compared to a smooth wall boundary layer. This local increase in velocity is believed to be the result of elastic transfer of free-stream energy to the near-wall motions by the E. clathrata filaments. Consequently, the usual assumption of the normal pressure gradient as a negligible second-order term for a normal zero-pressure gradient boundary layer may not be valid for the present kind of roughness. The LDV velocity measurements near and within the roughness layer have large uncertainties due to interference of the probe volume by the E. clathrata filaments. Above the roughness, the pitot-static tube and LDV profiles show relatively good agreement. It is concluded that for accurate prediction of the wall shear stress with E. clathrata-type of bio-fouling roughness, the Clauser velocity loss function should include a form drag factor instead of only the viscous drag factor.
Experimental Study of Breakaway Highway Sign Connections
Journal of Transportation Engineering, 2002
Some recent studies with irregular roughness suggest that the Nikuradse [Nikuradse, J., NACA TM 1... more Some recent studies with irregular roughness suggest that the Nikuradse [Nikuradse, J., NACA TM 1292, National Advisory Committee on Aeronautics (1933)] equivalent sand-grain roughness measure gives inconsistent results of the flow characteristics. In situations where the roughness is very strong to stifle or diminish the viscous effects the viscous scaling laws alone will not be very meaningful. The present study aims to find an alternative scaling parameter for such cases. Here, the measured mean and turbulent velocity profiles on a nonuniform roughness surface, simulating a gas turbine blade roughness, are presented. A nonzero wall normal pressure gradient is caused which is believed to contribute to the velocity deficit in the near-wall rough boundary layer velocity profile. The surface pressure variation is also directly influenced by the local roughness. The normal turbulent stresses are increased on the rough surface, the vertical component more than the longitudinal component. A pressure gradient velocity scale (similar to that proposed for adverse pressure gradient boundary layer modeling by Durbin and Belcher [Durbin, P.A. and Belcher, S.E., J. Fluid Mech. 238 (1992), 699–722] is defined to capture the pressure effects induced by such roughness on the inner layer properties.
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Papers by Chelakara Subramanian