Jaikrishnan R. Kadambi

A Transport Model for the Deterministic Stresses Associated With Turbomachinery Blade Row Interactions

The unsteady process resulting from the interaction of upstream vortical structures with a downstream blade row in turbomachines can have a significant impact on the machine efficiency. The upstream vortical structures or disturbances are transported by the mean flow of the downstream blade row, redistributing the time-average unsteady kinetic energy (K) associated with the incoming disturbance. A transport model was developed to take this process into account in the computation of time-averaged multistage turbomachinery flows. The model was applied to compressor and turbine geometry. For compressors, the K associated with upstream two-dimensional wakes and three-dimensional tip clearance flows is reduced as a result of their interaction with a downstream blade row. This reduction results from inviscid effects as well as viscous effects and reduces the loss associated with the upstream disturbance. Any disturbance passing through a compressor blade row results in a smaller loss than if the disturbance was mixed-out prior to entering the blade row. For turbines, the K associated with upstream two-dimensional wakes and three-dimensional tip clearance flows are significantly amplified by inviscid effects as a result of the interaction with a downstream turbine blade row. Viscous effects act to reduce the amplification of the K by inviscid effects but result in a substantial loss. Two-dimensional wakes and three-dimensional tip clearance flows passing through a turbine blade row result in a larger loss than if these disturbances were mixed-out prior to entering the blade row.

Particle sizing using particle imaging velocimetry for two-phase flows

Abstract The major factors influencing the successful measurement of particle size from Particle Imaging Velocimetry (PIV) image data are described. Components of a standard PIV system, a high resolution CCD camera and argon ion laser, are used to capture images of stationary particles. The image data are used to ascertain the limitations of estimating particle size. The effects of the Gaussian distributed intensity variation across the depth of the light sheet and the optical collection systems depth of field are investigated. These effects provide insight into designing a balanced illumination and collection optical system necessary to obtain constant particle size estimates, independent of their position within the light sheet. Using a ‘balanced’ optical set-up, monodisperse particle images are shown to be reproducible and predictable over a range of particle sizes and fields of view. Accuracy in the particle size estimates on the order of 9% are obtained consistently. It is also shown that size distributions in a mixture of polydisperse particles can be obtained with a maximum deviation of 10–20% from the true size distribution.

Experimental investigation and computational modeling of hydrodynamics in bifurcating microchannels

Methods involving microfluidics have been used in several chemical, biological and medical applications. In particular, a network of bifurcating microchannels can be used to distribute flow in a large space. In this work, we carried out experiments to determine hydrodynamic characteristics of bifurcating microfluidic networks. We measured pressure drop across bifurcating networks of various complexities for various flow rates. We also measured planar velocity fields in these networks by using particle image velocimetry. We further analyzed hydrodynamics in these networks using mathematical and computational modeling. Our results show that the experimental frictional resistances of complex bifurcating microchannels are 25–30% greater than that predicted by Navier–Stokes equations. Experimentally measured velocity profiles indicate that flow distributes equally at a bifurcation regardless of the complexity of the network. Flow division other than bifurcation such as trifurcation or quadruplication can lead to heterogeneities. These findings were verified by the results from the numerical simulations.

Investigations of Particle Velocities in a Slurry Pump Using PIV: Part 1, The Tongue and Adjacent Channel Flow

Transport of solid-liquid slurries in pipeline transport over short and medium distances is very important in many industries, including mining related processes. The particle image velocimetry technique was successfully utilized to investigate the velocities and kinetic energy fluctuations of slurry particles at the tongue region of an optically-clear centrifugal pump. The experiments were conducted using 500 micron glass beads at volumetric concentrations of 2.5% and 5% and at pump speeds of 725 rpm and 1000 rpm. The fluctuation kinetic energy increased approximately 200% to 500% as the pump speed was increased from 725 rpm to 1000 rpm. The directional impingement mechanism is more significant at the pressure side of the blade, tongue and the casing. This mechanism becomes more important as the speed increases. This suggests that the impeller, tongue and the casing of the slurry pump can wear out quickly, especially with an increase in speed. In this paper the emphasis is on the tongue region. The random impingement mechanism caused by the fluctuation kinetic energy of the solids can play an important role on the erosion of the tongue area.

PIV Investigations of the Flow Field in the Volute of a Rotary Blood Pump

ABSTRACT A full-size acrylic model of a rotary blood pump was developed in order to utilize Particle Image Velocimetry (PIV) to make measurements of the fluid velocities and turbulent stresses throughout the device. The development of an understanding of the hemodynamics within the blood pump is critical to the development and validation of computational models. A blood analog solution, consisting of sodium iodide solution and glycerin, was developed to match physiological kinematic viscosity. The refractive indecies of the fluid, the pump casing and the impeller were matched to facilitate the use of PIV to make velocity measurements. Velocity measurements made in the volute exit/diffuser region are presented for pumps speeds of 3000-3850 rpm. At each speed data were obtained at a physiological pressure of 90 mmHg and at a maximum flow condition. Four hundred data pairs were used for each resultant mean velocity vector value, representing greater than an order of magnitude more data pairs than reported previously in the literature on similar devices and resulting in velocity uncertainty levels of approximately ±2.9%.

Discrimination between solid and liquid velocities in slurry flow using laser Doppler velocimeter

Abstract A method to discriminate between solid and liquid velocities in a refractive index matched solid-liquid slurry flow has been developed. The matching of the refractive index of the solid and liquid allows the use of non-intrusive two color backscatter mode laser Doppler velocimeter (LDV) to measure the local solid and liquid velocities. A horizontal pipe flow configuration is used. Silica gel particles of mean diameter 40 μm and 50% sodium iodide solution are used as the refractive index matched solid and liquid, respectively. A signal processing technique which utilizes histograms of velocity along with signal amplitude discrimination is developed for differentiating between the solid and liquid velocities in the refractive index matched slurry. The technique utilizes the peaks in the velocity histogram that are associated with the local solid and liquid velocity data. Signal amplitude discrimination is used for identifying the histogram peaks associated with the solid and liquid velocities respectively and obtain the velocity distributions for the solid and the liquid in the histogram. This technique has been successfully applied to the slurry flows of low turbulence intensity (≤10%) with volumetric concentration as high as 25% in the heterogeneous and saltatin flow regimes.

Study of the flow properties of slurries using the refractive index matching technique LDV

Abstract Modern light scattering instrumentation cannot be applied to many concentrated slurries because they are opaque. In this study Laser Doppler Velocimetry is used to measure liquid solid axial velocity profiles for refractive index matched slurries with solids loadings as great as 25 vol.%. Since measurements in flow geometries more complex than straight horizontal pipe are of interest in many applications, axial velocity profiles through a concentric contraction are reported. The usefulness of these measurements from an experimental perspective a modeling perspective is discussed. The theoretical analyses of Hanks and Dadia Hanks and Ricks were applied to the flow data through the constant-diameter pipe. Flow regimes are identified where these theories are appropriate.

The Effect of Steady Aerodynamic Loading on the Flutter Stability of Turbomachinery Blading

An aeroelastic analysis is presented that accounts for the effect of steady aerodynamic loading on the aeroelastic stability of a cascade of compressor blades. The aeroelastic model is a two-degree-of-freedom model having bending and torsional displacements. A linearized unsteady potential flow theory is used to determine the unsteady aerodynamic response coefficients for the aeroelastic analysis. The steady aerodynamic loading was caused by the addition of (1) airfoil thickness and camber and (2) steady flow incidence. The importance of steady loading on the airfoil unsteady pressure distribution is demonstrated. Additionally, the effect of the steady loading on the tuned flutter behavior and flutter boundaries indicates that neglecting either airfoil thickness, camber, or incidence could result in nonconservative estimates of flutter behavior.

Comparison of Particle Image Velocimetry and Laser Doppler Anemometry Measurements in Turbulent Fluid Flow

PAC00: 8763Lk, 4262Be, 8719Uv, 8719Hh, 8780-y

Cyclonic two-phase flow separator experimentation and simulation for use in a microgravity environment

Devices designed to replace the absent buoyancy separation mechanism within a microgravity environment are of considerable interest to NASA as the functionality of many spacecraft systems are dependent on the proper sequestration of interpenetrating gas and liquid phases. Cyclonic separators provide the gas-liquid separatory action by swirling the multiphase flow – causing the gas to accumulate along the axis of the vortex as the denser liquid is forced to the walls – thereby allowing segregated extraction of the respective phases. Passive cyclonic separators utilize only the inertia of the incoming flow to accomplish this task. In the current work, combined experimental, numerical, and scaling analyses have been performed to quantitatively assess and delimit the operability of these separators. Specifically, steady-state features including velocity profiles have been examined experimentally and compared to computational fluid dynamics results, scaling laws for the gas core size have been created, and the transient behavior of the device with respect to both device and system-level conduct has been modeled.