O. P. Singh

On the relationship between finger width, velocity, and fluxes in thermohaline convection

Double-diffusive finger convection occurs in many natural processes.The theories for double-diffusive phenomena that exist at present consider systems with linear stratification in temperature and salinity. The double-diffusive systems with step change in salinity and temperature are, however, not amenable to simple stability analysis. Hence factors that control the width of the finger, velocity, and fluxes in systems that have step change in temperature and salinity have not been understood so far. In this paper we provide new physical insight regarding factors that influence finger convection in two-layer double-diffusive system through two-dimensional numerical simulations. Simulations have been carried out for density stability ratios (R-rho) from 1.5 to 10. For each density stability ratio, the thermal Rayleigh number (Ra-T) has been systematically varied from 7x10(3) to 7x10(8). Results from these simulations show how finger width, velocity, and flux ratios in finger convection are interrelated and the influence of governing parameters such as density stability ratio and the thermal Rayleigh number. The width of the incipient fingers at the time of onset of instability has been shown to vary as Ra-T-1/3. Velocity in the finger varies as Ra(T)1/3/R-rho. Results from simulation agree with the scale analysis presented in the paper. Our results demonstrate that wide fingers have lower velocities and flux ratios compared to those in narrow fingers. This result contradicts present notions about the relation between finger width and flux ratio. A counterflow heat-exchanger analogy is used in understanding the dependence of flux ratio on finger width and velocity.

Effect of Rayleigh numbers on the evolution of double-diffusive salt fingers

This is a transient two-dimensional numerical study of double-diffusive salt fingers in a two-layer heat-salt system for a wide range of initial density stability ratio (Rρ0) and thermal Rayleigh numbers (RaT∼103 − 1011). Salt fingers have been studied for several decades now, but several perplexing features of this rich and complex system remain unexplained. The work in question studies this problem and shows the morphological variation in fingers from low to high thermal Rayleigh numbers, which have been missed by the previous investigators. Considerable variations in convective structures and evolution pattern were observed in the range of RaT used in the simulation. Evolution of salt fingers was studied by monitoring the finger structures, kinetic energy, vertical profiles, velocity fields, and transient variation of Rρ(t). The results show that large scale convection that limits the finger length was observed only at high Rayleigh numbers. The transition from nonlinear to linear convection occurs at ...

Optimization of Air-Cooling System of 4-Stroke Scooter Engine

We present the results from the 3-D numerical simulations on the optimization of the fan-cooling system in a two-wheeler 4-stroke single cylinder engine. Objective was to optimize the flow rate and distribution of flow over the engine surfaces to keep the maximum temperature of engine oil and engine surfaces well within the lubrication and material limit respectively at the expense of minimum increase in fan power. This work aimed at reducing the engine oil temperature by 20°C. Combined flow and heat transfer analysis (Conjugate analysis) was conducted with the engine head and block modeled as solid medium and fan cooling system modeled as fluid medium. ReynoldsAveraged-Navier-Stokes turbulence (RANS) equations along with energy equation were solved to get the flow field and temperature distributions inside the cooling system and on the engine surfaces respectively. Moving Reference Frame approach was used for simulating the rotation of fan. Cowl geometry was modified for providing better guidance to flow over engine surfaces and to get maximum utilization of cooling capacity of flowing air. Fan size and blade shape were altered to increase the flow rate and reduce fan power consumption. Flow parameters in the cooling path and temperatures at engine surfaces were validated against the experimentally measured values on test rig. The final design gave a 24°C reduction in oil temperature and 3.1% reduction in fan power, while maintaining same flow rate.

Salt finger convection at marginal stability

Abstract Double diffusive salt fingers are alternating rising and falling convective structures that form due to density variation driven by varying diffusivity of the components. The degree of compensation between the component in terms of their effects on density stratification is measured by a dimensionless quantity, density ratio (). Salt fingers can form when density stability ratio lies in the range , where is the diffusivity ratio. However, lately a new finger regime has been observed in the experiments of Hage and Tilgner [Phys. Fluids, 2010, 22, 076603–076607], where finger convection occurs even for . It is observed in oceans that salt finger forms at low and distinctive finger formation occurs when . However, critical information such as convective structures and fluxes are still unknown concerning what exactly happens at marginal stability (). There has been a comprehensive study of salt finger convection at but scarcely any literature exists that has explored finger behaviour at . In this paper we study the unexplored finger convection regimes numerically in a large range of governing parameter, for systems initially at .

INFLUENCE OF GEOMETRIC PARAMETERS ON CENTRIFUGAL FAN PERFORMANCE AND ITS SIGNIFICANCE IN AUTOMOTIVE APPLICATIONS

In this paper, the effect of geometrical parameters of centrifugal fan on performance has been presented with a system approach. Often, the operators or the design engineers focus on the immediate requirements of the engine/equipment and they neglect the broader question of how the fan parameters are affecting the equipment. For instance, change in fan angles will change the performance e.g., airflow rates and efficiency. However, it also affects the contaminants build-up on the blades. Blade angle with higher angle of attack will promote contaminants build-up on blade surfaces, which in turn causes performance degradation and unstable operation. The system approach in fan parameter selection will result in a more reliable system. Significance of other fan parameters is also discussed. We present an experimental setup and validated computational fluid dynamic (CFD) model. Fan power consumption is determined experimentally and compared with the CFD model. Further parametric simulations were carried out to investigate the effect on fan performance. Effect of system resistance, inlet and outlet angle, blade thickness, and no-uniform spaced blades has been described with discussions on industrial relevance. A fan with higher flow rates is desirable to reduce engine temperatures and enhance the durability. However, higher flow rates result in more fan power consumption at a given fan speed. The test results suggest that a fan with higher power coefficient does not affect the vehicles mileage significantly. This paper will help design engineers in making informed decision about the interaction between the fans and system, and its effect during the operation.

Effect of Rayleigh Number and Density Stability Ratio on characteristics of Double-Diffusive Salt Fingers

In this paper, we investigate the finger evolution pattern and physics behind the layer formation in a two layer model using numerical simulations. A three-dimensional (3D) numerical code has been developed to solve Navier-Stokes equations along with energy and concentration conservation equations. Simulations were carried out to study the effect of Rayleigh number and density ratio on the characters of salt finger. Instabilities in form of rolls grow from side walls in all simulated cases. Square planform is found to be stable only at low Ra T . Individual components flux is found to be larger in 3D case compared to 2D, but the flux ratio is found to be less in 3D.

Computer Aided Modeling and Finite Element Analysis of Human Elbow

Finite element modeling (FEM) plays a significant role in the design of various devices in the engineering field of automotive, aerospace, defense etc. In the recent past, FEM is assisting engineers and healthcare professional in analyzing and designing various medical devices with advanced functionality. Computer aided engineering can predict failure circumstances, which can be avoided for the health and well-being of people. In this research work, computer aided engineering analysis of human elbow is presented beginning with modeling of human elbow from medical image data, and predicting the stresses in elbow during carrying heavy loads. The analysis is performed by using finite element method. The results predict the stress level and displacement in the human bone during heavy weight lifting. Thus, it can be used to predict the safe load that a particular person can carry without bone injury. The present analysis focused on a particular model of bone for a particular individual. However, safe load can be determined for various age groups by generating more detailed model including tendons, ligaments and by using patient specific material properties. KEywoRdS Finite Element Method, Human Elbow, ITK-SNAP, Medical Imaging, Safety

Optimum knock sensor location through experimental modal analysis of engine cylinder block

The knock sensor is provided on an engine cylinder block to detect abnormal engine combustion (knocking) and to provide feedback to engine control unit (ECU). The ECU then modifies the engine input and avoids knocking. A commonly used knock sensor is an accelerometer that detects cylinder wall vibration and estimates knocking of the engine. Selecting the location of a knock sensor in many cases involves a challenging trial and error approach that depends upon the measurement of the knock signal at many locations on engine structure. However, a cylinder block exhibits many structural resonances. Thus, a large vibration signal at the surface of cylinder block can be either due to knocking of the engine or due to the resonances of the cylinder block structure because of normal excitation forces. Hence, this conventional method does not always yield reliable results. The aim of the work reported in this paper is to experimentally determine the inherent dynamic characteristics of a cylinder block and to combine this with a calculation of the fundamental knock frequency and, thus, to identify the optimum location for the knock sensor.