bluuebunny/crossref_metadata_2025 huggingface dataset:
Inverse Calculation of Flame Impingement Heat Transfer
Authors: Ahmed Ikram , Sabirov Ildar
Published: September 2008

Inverse calculations are presented here for the estimation of heat transfer from an impinging flame on a flat surface. This work is a preliminary exercise for estimating heat transfer from an impinging plasma jet, where direct measurements can be very difficult and costly, and the correlations based on air or water jet impingement measurements may not be applicable because of the very high temperature (and property) gradients. As the gas flame impinges on an initially cold flat plate, the temperature evolution on the backside is recorded using an infrared camera. The time–temperature data thus obtained are then compared with those predicted by a finite volume method based code. The code uses a polynomial series for estimating the convection coefficient, which varies with radial distance. The coefficients of this polynomial are treated as a set of parameters to be estimated through the Levenberg-Marquardt approach. The results obtained so far indicate that it may be possible to use such an approach for estimating heat transfer from a plasma jet.
Representing Polydispersed Droplet Behavior in Nucleating Steam Flow With the Quadrature-Method-of-Moments
Authors: Mousavi A. , Gerber A. G. , Kermani M. J.
Published: September 2008

This paper applies the Quadrature-Method-of-Moments (QMOM) to the polydispersed droplets spectrum typical in low pressure steam turbines. Various modes of nonequilibrium phase transition are present in steam turbines, starting with primary and secondary homogeneous nucleation as the main source of moisture followed by heterogeneous nucleation and surface entrainment sources. The range of phase transition possibilities leads to a wide range of droplet sizes, which are present under various combinations of inertial and thermal nonequilibrium. Given the extensive prevalence of CFD in turbomachinery design, it is of interest to develop an efficient modeling approach for polydispersed droplet flows that avoids solving an excessive number of equations to represent the droplet size distribution. Methods based on QMOM have shown promise in this regard in other applications areas of two-phase flow, and this paper attempts to quantify its potential for steam turbine applications by applying the method to supersonic nozzle studies with homogeneous and heterogeneous phase transitions.
Inhomogeneous Multiphase Model for Nonequilibrium Phase Transition and Droplet Dynamics
Authors: Gerber A. G.
Published: September 2008

This paper describes the development of an inhomogeneous multiphase model for the prediction of phase transition and nonequilibrium droplet dynamics under transonic flow conditions. The primary application of interest is low pressure steam turbines, where high speeds and complex geometry result in a second phase exhibiting significant droplet size variation, with associated thermal and inertial nonequilibrium relative to the vapor phase. The formulation uses a pressure based, implicit in time, algorithm with finite-volume/finite-element discretization of the conservation equations. For each phase, the velocity, energy state, volume fraction and droplet number are computed. For a two material phase system (water vapor and liquid) a parent and any number of (source based) condensed liquid phases are possible to handle the variety (and complexity) of droplet behavior as found in low pressure steam turbines. The model is tested against experimental data available in the steam turbine community. In particular the influence of inertial nonequilibrium on the phase transition behavior in a steam turbine cascade geometry is examined.
Analysis of Thermodynamic Effects on Cavitation Instabilities
Authors: Watanabe Satoshi , Hidaka Tatsuya , Horiguchi Hironori , Furukawa Akinori , Tsujimoto Yoshinobu
Published: September 2008

The suction performance of turbopumps in cryogenic fluids is basically much better than that in cold water because of thermodynamic effect of cavitation. However, it is not still clear how the thermodynamic effect works on cavitation instabilities such as rotating cavitation and cavitation surge. In the present study, the unsteady heat exchange between cavity and surrounding liquid is taken into account in a stability analysis using a singularity method. The results are qualitatively compared with existing experiments to clarify the research needs for deeper understanding.
Determination of Pump Impeller Deflections: Comparison of FSI-Simulations to Measurements
Authors: Benra Friedrich-Karl , Dohmen Hans Josef , Wan Bo
Published: September 2008

The determination of pump rotor oscillations induced by exciting hydrodynamic forces requires both a solution of the flow field in the pump and an analysis of the structural mechanics of the pump rotor. In the present contribution, simulations which accomplished different coupling methods between the fluid dynamic solution and the structural analysis were carried out for a single-blade pump. In a first approach a one way coupling was used to determine the oscillations of the pump impeller during operation. The forces calculated from the transient flow field were treated as a load acting at the impeller. A comparison of the computed oscillations to measurements showed that in the present case the strong physical interaction between the flow and the impellers structure requires the feedback of the structural analysis to the flow solution to give more meaningful results. In a second approach a simulation was carried out, which accomplished a full coupling of the fluid dynamics and the structural dynamics. Both physics were solved alternating and at least two iterations, one for each physics, were needed to achieve the required coupled response. The calculations were coupled by passing loads across the physics field interfaces. In the present example, for each regarded time step during one impeller revolution, the pressure field acting at the impeller surface was transferred from the CFD solver to the structural solver as the load on the impeller and the computed deflection of the impeller was transferred back deforming the computational grid of the fluid volume.
Particle Collision Effect on Turbulent Prandtl Number in Gas-Solid Flows
Authors: Mansoori Zohreh , Saffar-Avval Majid , Basirat-Tabrizi Hasan , Ahmadi Goodarz , Ramezani Payam
Published: September 2008

Traditional gas-solid turbulence models using constant or the single-phase gas turbulent Prandtl number cause error in the thermal eddy diffusivity and thermal turbulent intensity fields calculation. The thermo-mechanical turbulence model is based on solving the hydrodynamic transport equations of the turbulent kinetic energy and turbulent time scale, beside the thermal turbulent equations of temperature variance and thermal turbulence time scale. This model has the ability to calculate the turbulent Prandtl number directly by computing the eddy viscosity and the thermal eddy diffusivity through the values of turbulence fluctuation velocity and thermal variances and time scales. A four way Eulerian/Lagrangian formulation was used to study the effect of particle properties on the turbulent flow and thermal fields, as well as on turbulent Prandtl number in a gas-solid developing pipe flow. Inter-particle collisions were included and the Lagrangian trajectory analysis was used. The earlier results showed that turbulent Prandtl number is influenced by the variations of gas and particle properties and also inter-particle collisions in a fully-developed riser. In the current study, the developing gas-solid flow region in a pipe was considered and the variation of turbulent flow field due to inter-particle collision was evaluated.
Lattice Boltzmann Thermal Flow Simulation and Measurements of a Modified SAE Model With Heated Plug
Authors: Fares Ehab , Jelic Sacha , Kuthada Timo , Schro¨ck David
Published: September 2008

This article presents the novel experiment of the modified SAE model with a heated plug and discusses the details about the new developments of the numerical model of the PowerFLOW 4.0 version, which employs a Lattice Boltzmann model and incorporates an improved unsteady two equations RNG k-ε turbulence model, a coupled PDE for the energy equation and an advanced wall model for both flow and thermal boundary layers. The hot flow is discussed both experimentally and numerically. Distributions of the flow field are compared with available experimental findings. The predictive capability and the feasibility of the current Lattice Boltzmann approach is demonstrated and the applicability to similar flows over realistic road vehicles is discussed.
Hydration Structure and Shear Viscosity of Water Nanoconfined Between Mica Surfaces
Authors: Leng Yongsheng , Cummings Peter T.
Published: September 2008

Molecular dynamics (MD) simulations have been performed to investigate the structure, shear viscosity and dynamics of hydration layers of the thickness of D = 0.61 ∼ 2.44 nm confined between two mica surfaces. For D = 0.92 ∼ 2.44 nm films, water O density distributions indicate that the hydration layers are in liquid phase. The corresponding shear responses are fluidic and similar to those observed in surface force balance (SFB) experiment. However, further increase in confinement leads to the formation of a bilayer ice (D = 0.61 nm) which shows significant shear enhancement and shear thinning over a wide range of shear rate in MD regime, consistent with recent experimental results by shear resonant apparatus for the two mica surfaces in registry.
Phase Locked Analysis of a Simplified Car Geometry Wake Flow Control Using Synthetic Jet
Authors: Leclerc Ce´dric , Levallois Euge´nie , Gallas Quentin , Gillie´ron Patrick , Kourta Azeddine
Published: September 2008

This paper presents a numerical unsteady analysis of a SJA impact on a car wake flow. First, for the optimal reduced frequency F+, the influence of the Cμ on the mean aerodynamic drag reduction 〈Cd〉 is observed. A spectral analysis of the vortex shedding coming from the upper and the lower part of the car and of the drag coefficient is then presented for different Cμ values. Preliminary results suggest that maximum drag reduction is obtained when most energy in the wake comes from the actuator forcing frequency rather than the natural vortex shedding frequencies of the two contributions. This work is completed by a phase locked analysis of the synthetic jet actuator local effect on the turbulent boundary layer just before the flow separation. For the fixed optimal F+, different Cμ values are compared. The streamwise velocity profiles seem to show that maximal efficiency of the control is obtained when the synthetic jet injected momentum is introduced in the logarithmic sub-layer part of the turbulent boundary layer.
Parametric Study and Computational Two-Phase Flow Simulation of the Refrigerant Distributor in a Spray Type Evaporator
Authors: Chien Liang-Han , Wang Shih-Ming , Lee Shu-Che
Published: September 2008

This manuscript presents a simplified model for the simulation of liquid-vapor flow in a spray type evaporator of a chiller unit. In the present study, the liquid and vapor phases are considered as two separate fluids and simulated by the commercial code, FLUENT. Two types of distributors were investigated: (1) a miniature tubular distributor, and (2) a full scale distributor. The tubular distributors consists of two tubes, the pore size (1.0 mm or 1.5 mm) of the inner tube and the gap size (1.0, 2.0 or 3.0 mm) of the outer tube were varied for comparisons of the velocity and pressure distributions. Three different flow rates: 1.6, 3.2 and 6.4 g/s, were set in the simulations of miniature distributor. The full scale distributor consists of a 30 mm diameter tube having 4.0 mm pores in 18 mm pitch, and a 2400 mm × 226 mm perforated plate having 3.0 mm pores. The Volume of Fluid model and the Continuum Surface Force model were used in the two-phase simulation of the full scale distributor. From the present study, we found that the 3.0 mm gap width yields the most uniform flow distribution for 1.6 ∼ 6.4 kg/s for the miniature distributor. Based on the simulation of the miniature distributor, a falling film evaporation test apparatus is designed, and uniform fluid distribution in the evaporator is found. The fluid distribution observed in the test of an 80 ton chiller is more uniform than that shown in the preliminary result of the full scale simulation.
Numerical Analysis of Turbulent Natural Convection Heat Transfer Inside a Trangular Shaped Enclosure Utilizing Computational Fluid Dynamic Code
Authors: Ghassemi M. , Fathabadi M.
Published: September 2008

Numerical study of turbulent natural convection heat transfer inside a triangular shaped enclosure is considered. A k-ε model along with mass, momentum and energy equations is utilized to solve the flow and temperature field. A computational fluid dynamic based code (CFD), Fluent, that is commercially available is used is to solve the non-linear partial differential equations. The steady state, two-dimensional, incompressible heat transfer results are presented in terms of non dimensional temperature, heat flux, and the Nusselt number as a function of aspect ratio (Ar), angle between sloped and horizontal wall (θ), and the Grashof number (Gr). The obtained results are compared with results that are calculated by a control volume based method. Results obtained by the Fluent code shows closed agreement with the control volume ones. It is again shown that heat transfer is higher in turbulent settings and results are function of the angle between two walls of the enclosure (θ).
Adiabatic Gas-Liquid Two-Phase Flow Patterns in Microchannels
Authors: Xiong Renqiang , Chung J. N.
Published: September 2008

Flow patterns of adiabatic gas-liquid two-phase flow in micro-channels were experimentally investigated. Using nitrogen and water, experiments were conducted in square micro-channels with hydraulic diameters of 0.209mm, 0.412mm and 0.622 mm, respectively. Gas and liquid superficial velocities were varied from 0.06–72.3 m/s and 0.02–7.13 m/s, respectively. Four defined flow patterns, bubbly-slug flow, slug-ring flow, dispersed-churn flow and annular flow, were observed in micro-channels of 0.412 mm and, 0.622 mm. In the micro-channel of 0.209 mm, the bubbly-slug flow became the slug-flow and the dispersed-churn flow disappeared due to the surface tension effect and the smooth gas-liquid interface. The flow regime maps for the current three micro-channels were constructed and showed the transition lines shifted to higher gas superficial velocity due to the stronger surface tension effect with a smaller channel size in micro-channels. They were also compared with some other micro-channel flow regime maps and the mini-channel flow regime map based on the Weber number model, which showed the flow map for the micro-channel is significantly sensitive to the working fluid, channel geometry and channel size and the flow regime criteria developed for mini-channels should not be applied for micro-channels without further verification.
Simulation of Subcooled Nucleate Boiling in a Vertical Annulus With Coupling of Bubble-Tracking and Two-Fluid Models: Further Comparison With Experimental Results
Authors: Kljenak Ivo , Koncˇar Bosˇtjan , Mavko Borut
Published: September 2008

A model of subcooled nucleate boiling flow in a vertical channel at low pressure conditions that was developed earlier is further validated by comparison of simulations with experimental results from Purdue University (USA). The model consists of a three-dimensional bubble-tracking model and a two-dimensional two-fluid model which are coupled off-line. By taking into account dynamic phenomena (liquid flow, bubble motion and interaction) and thermal phenomena (liquid heating, bubble nucleation and condensation), the model is able to simulate the gradual evolution of void fraction profiles along the boiling channel.
Analyze and Control of Near-Wake Flow on a Simplified Car Geometry
Authors: Roume´as M. , Gillie´ron P. , Kourta A.
Published: September 2008

A 3D numerical simulation, based on the Lattice Boltzmann Method is carried out on a rectangular body (initially proposed by Ahmed [1]) to analyze the influence of blowing devices on the near-wake flow of a generic blunt body model. First, the results obtained without control are compared with experimental data from the literature. An open loop flow control strategy is then applied by setting blowing slots around the periphery of the body base. The blowing velocity is set to 1.5 V0, V0 being the upstream velocity. The resulting aerodynamic drag reduction is then analyzed by studying velocity, vorticity and total pressure loss distributions in the near-wake flow. Typical results show that a 29% drag reduction is obtained at a blowing angle of θ = 45° with respect to the base surface. Blowing jets are analogous to separated longitudinal fluidic elements which permit to reduce the transversal wake section by inclining the streamlines in the near-wake flow. The momentum introduced into the flow leads to a reduction in the wake total pressure loss and an increase in the base static pressure distribution. Finally, a parametric analysis is conducted on the blowing velocities in order to optimize the efficiency of the chosen control strategy, i.e. to minimize the ratio between the energy used to generate the jets and the energy saved through aerodynamic drag reduction.
Comparison of the Unsteady Loads of an Airfoil in the Pitching and Plunging Motions
Authors: Soltani M. , Seddighi M. , Rasi F.
Published: September 2008

A series of experiments were conducted on an oscillating airfoil in subsonic flow. The model was oscillated in two types of motions, pitch and plunge, at different velocities, and reduced frequencies. In addition, steady data were acquired and examined to furnish a baseline for analysis and comparison. The imposed variables of the experiment were reduced frequency, mean incident angle, amplitude of motion, and free stream velocity as well as the surface grit roughness. The unsteady aerodynamic loads were calculated using surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces of the model. Particular emphases were placed on the effects of different type of motion on the unsteady aerodynamic loads of the airfoil at pre-stall, near stall, and post stall conditions. Variations of the aerodynamic coefficients with equivalent angle of attack for both pitching and plunging motions showed strong sensitivity to the reduced frequency, oscillation amplitude, Reynolds number, and mean angles of attack.
Impact of Heat Transfer on Contaminant Dispersion in a Public Building
Authors: Haupt Sue Ellen , Kunz Robert F. , Peltier L. Joel , Dreyer James J. , Gibeling Howard J.
Published: September 2008

Computational fluid dynamics (CFD) models are effective at predicting dispersion of contaminants in or near a building. It is well known that thermal effects impact the flow around and within structures. This study assesses the importance of time of day, building materials, sky cover, etc. on the local thermal heating of a building. All these features affect the buoyancy, and thus, the resulting flow and dispersion about and inside a building. This study examines that impact through including full thermal coupling with flow calculations for an environmentally friendly building, including thermal radiation, conduction, and convection effects with a CFD model for both the interior and exterior of a building. The emphasis here is on simulating the impact of heating on contaminant dispersion.
Linear Stability Analysis of Chevron Jet Profiles
Authors: Gudmundsson Kristjan , Colonius Tim
Published: September 2008

We investigate the linear stability characteristics of the mean velocity profiles produced by chevron nozzles. We show that chevron instability waves can be decomposed into azimuthal modes analogously to those of round jets. This facilitates a direct comparison of growth rates and mode structure between different nozzles. We find that the three nozzles used in this study share a set of modes, referred to as primary modes. In addition, we find that there exist modes unique to the chevrons nozzles, termed secondary modes. While chevron jets possess a much larger number of unstable modes, the modes with lowest azimuthal structure show strong suppression of growth rates in two different chevron jets. Some preliminary implications on sound generation are discussed.
Vortex Flow Behind an Unsteady Airfoil in Pitching and Heaving Motions and Dynamic Thrust
Authors: Fuchiwaki Masaki , Tanaka Kazuhiro
Published: September 2008

The detailed vortex flow structure behind a combination airfoil at a low Reynolds number region was measured by PIV. Moreover, the dynamic thrust acting on a combination airfoil was measured by a six-axes sensor in water tunnel. The combination airfoil can form clear thrust producing vortex street behind airfoil even at low non-dimensional trailing edge velocity and non-dimensional heaving velocity. Especially, it is possible to form the thrust producing vortex street with high vorticity at φ = π/2 and π. The jet velocity behind combination airfoil at φ = π/2 and π becomes over 2.0. The averaged dynamic thrust acting on a combination airfoil increases as the non-dimensional trailing edge velocity and non-dimensional heaving velocity increases, same as case in pitching and heaving airfoils. Moreover, the averaged dynamic thrust acting on combination airfoil at φ = π/2 and π is much larger than that on pitching and heaving airfoils. However, the maximum thrust efficiency of a combination airfoil at φ = π/2 was approximately 0.42 and was slightly higher than that on a pitching airfoil.
3-D Modelling of Brownian Motion of Nano-Particles in Aerodynamic Lenses
Authors: Nikbakht Abbas , Abouali Omid , Ahmadi Goodarz
Published: September 2008

A computer code for analyzing nano-particle motions in an aerodynamic particle beam focusing system was developed. The effectiveness of the focusing system consisting of several lenses, nozzle and downstream tube of the nozzle was analyzed. The code included an accurate 3-dimensional model for the Brownian diffusion of nano-particles in sharply varying pressure field in the aerodynamic lens system. Lagrangian particle Trajectory analysis was performed assuming a one-way coupling model. The particle equation of motion used included drag and Brownian forces. Trajectories of different size nano-particles in an aerodynamic lens were analyzed, and the particle beam focusing process was studied. The numerical results of 3-D model for particle beam diameter, penetration efficiency and beam divergence angle were compared with axisymmetric model and discussed. The importance of the accuracy of the computational model for the simulation of the Brownian diffusion for predicting the focusing performance of the aerodynamic lenses was discussed. The simulation results showed that for particle diameters less than 50 nm in helium, the Brownian force could significantly affect the beam focusing and particle collection efficiency. Furthermore, the nano-particle trajectories in this range are three-dimensional and an axisymmetric model may not correctly capture the features of particle motions in aerodynamic lenses.
Dropwise Condensation Heat Transfer Model: Effect of the Liquid-Solid Surface Free Energy Difference
Authors: Ma Xue-Hu , Lan Zhong , Zhang Yu , Zhou Xing-Dong , Sun Tian-Yi
Published: September 2008

Dropwise condensation heat transfer performance depends not only on the condensing conditions, but also on the interfacial interaction between condensate and condensing surface material. Based on the well-established Rose’s model, a modified model of dropwise condensation heat transfer is proposed by considering the interfacial interaction between liquid and solid, and established by rebuilding the space conformation of drop distributing into time conformation. The simulation results indicate that the heat transfer coefficient increases with the surface free energy difference increasing and the contact angle hysteresis decreasing. The larger contact angle and the smaller departure drop size result in the higher heat transfer coefficient. Different interfacial effect gives rise to the different heat transfer curves. For the identical solid-liquid-vapor system, the simulation results agree very well with the present experimental data and those reported in literature. The controversy among experimental results in literature might be well understood with the concept of the present paper.
Effect of Surface-Free-Energy-Difference on Condensation Characteristic Curves of Binary Mixture of Steam and Ethanol Vapor
Authors: Ma Xue-Hu , Lan Zhong , Zhou Xing-Dong , Zhang Yu
Published: September 2008

The condensation heat transfer process of binary mixture of steam and ethanol vapor was studied experimentally with various ethanol concentrations and surface subcooling at atmospheric pressure. The experiments demonstrate that the condensation modes alter from filmwise, to transition and finally to dropwise with respect to the operation conditions. The marangoni effect was always used to interpret this phenomenon in the published literature. In this paper, the mechanism of condensation heat transfer with the liquid-solid-surface-free-energy-difference is used to further understand this process and the conversion of condensation modes. From this viewpoint, the condensation characteristics of binary mixture of steam and ethanol vapor can be explained reasonably with the corresponding condensation modes. Base on the data of the present paper and those reported in literature, the conversion criterion of the condensation modes is proposed. The condensation state is filmwise for the surface-free-energy-difference less than 14±1 mJ·m−2 and dropwise for more than 21±1 mJ·m−2 and transition for between 14±1 mJ·m−2 and 21±1 mJ·m−2.
Calibrated POD Reduced-Order Models of Massively Separated Flows in the Perspective of Their Control
Authors: Favier J. , Cordier L. , Kourta A. , Iollo A.
Published: September 2008

Lots of studies have been performed to control boundary layer separation. In order to develop a control procedure that is energetically efficient, it is interesting to formulate active flow control problems like optimization problems [1]. To reduce the numerical costs associated to this approach, a POD Reduced-Order Model is used instead of the high-fidelity model formed by the Navier-Stokes equations. Resolving this low-order dynamical system provides the dynamics of the flow on the POD subspace and using the optimal control theory, it is possible to find the optimal control law determined on the low-fidelity model [2]. In the present paper, DNS velocity fields of the wake flow behind a circular cylinder and PIV measurements of a separated flow around an airfoil are used to build and calibrate low order models.
Computational Modeling of a Cell-Based Microphysiometer
Authors: Eluvathingal Sebastian J. , N’Dri Narcisse A. , Stremler Mark , Cliffel David
Published: September 2008

A computational model of a cell-based microphysiometer is presented in this paper. The microphysiometer is a fluid based device that uses electrochemical sensors to measure the concentration of metabolites in the fluid medium around living cells. A computational code has been used to model the convective-diffusive transport in this system. This work focuses on modeling an oxygen electrochemical sensor. An ideal sensor model is used to study the effects of initial concentration and cell uptake rate on the sensor signal. In particular, the relative influence of the oxygen consumption by the sensor and the cells is examined. Removing the effect of the sensor allows isolation of cell behavior for various cell uptake rates and ranges of initial concentration. A preliminary comparison of computational results with experimental data is presented. The computational model provides very useful predictions of trends.
Numerical Analysis of Unstable Flow in Last-Stage Blades of Steam Turbines
Authors: Garci´a J. C. , Kubiak J. , Sierra F. , Gonza´lez G. , Urquiza G.
Published: September 2008

As well known steam turbines are strongly affected because of vibrations. Unstable vibrations can appear together with steady-state vibrations. We present the results of numerical computations about unstable flow and its interaction on blades of steam turbines, which can lead to unstable modes of vibration. Unstable phenomena appear as a result of interaction of blades with the stream of steam flow where the pressure field provides the force. The analysis centers particularly in the last stage or L-0 of a 110 MW turbine. Navier-Stokes equations are resolved in two dimensions using a commercial program called Fluent based on finite-volume method. A 2-D geometry model was built in order to represent the dimensional aspects of the diaphragm as well as the rotor located in the last stage of the turbine. Periodic boundary conditions were applied to both sides of the blade with the purpose of simplifying the computation avoiding resolve for the whole wheel. The computations were conducted in both modes, steady state and time dependent. The results show the distribution of pressure fields as a function of the distance to the exit edge of the diaphragm blades. Also, the pressure and velocity fields are shown through contours along the flow channel between the diaphragm blades. The paper includes the time-dependence behavior of pressure field. A Fourier analysis is used to determine the characteristic frequencies of the system, based on numerical results.
Flow Visualisations and PIV Measurements of ZNMF Jet Control of Separated Flow Over NACA0015 Airfoil
Authors: Soria Julio , Stephens Trevor , Tuck Ashley
Published: September 2008

This paper presents and describes the results of an experimental study into the control of separated flow over a NACA0015 airfoil over a range of angles of attack at a Reynolds number of 3 × 104. The study was carried out in the LTRAC 500 mm × 500 mm water tunel. The separation control is actuated using a planar zero-net-mass-flow (ZNMF) jet at the leading edge of the airfoil. The ZNMF micro-jet flow is generated using a piston-cylinder arrangement connected to a skotch-yoke mechanisms that is driven by a computer controlled stepper motor. The parameter range for the planar ZNMF jet ranged from non-dimensional frequency of 0.5 to 1.5 and blowing coefficients up to 0.2. A six component force transducer was used to measure the lift and drag force on the airfoil. Planar laser induced fluoresence (PLIF) using Kyton red dye and Nd:YAG laser illumination was used for the flow visualisations. Multigrid cross-correlation digital PIV (MCCDPIV) with pulsed Nd:YAG laser planar illumination was employed with digital imaging of 4008 px × 2672 px to measure instantenous velocity fields.
Uncertainty Examination of New Water Flow Calibration Facility for Nuclear Power Application
Authors: Sato Hiroshi , Furuichi Noriyuki , Terao Yoshiya , Takamoto Masaki
Published: September 2008

A new test facility has been constructed at National Metrology Institute of Japan (NMIJ) for calibration of feed water flowmeters at nuclear power stations for Reynolds numbers of up to 16 million. This very large Reynolds number is achieved at a flow rate of 3.33 m3/s (12,000 m3/h) and water temperature of 70 degrees C in a 600 mm pipe. This new facility has four sets of pumps and reference flowmeters installed in parallel upstream of the test section. These flowmeters are calibrated at 0.83 m3/s (3,000 m3/h) one by one without dismounting from the loop by using a 50 t weighing tank; this tank has been used as the primary standard for the existing flow facility. Then the flow rate can be increased up to 3.33 m3/s (12,000 m3/h) with all of the pumps and flowmeters working at the same time. This paper describes the concept of the new facility, the fundamental uncertainty estimation, and the examination of its measurement capability.
Conservation Low of Centrifugal Force and Its Application to Fluid Flow in Turbomachinery
Authors: Tanaka Takaharu
Published: September 2008

Theoretical pump head is discussed and the conservation low is introduced on Centrifugal force. Theoretical head obtained by the application of conservation law on fluid flow in rotating flow passage is formed as the difference between the head obtained at the impeller outlet and that at impeller inlet. Conservation low of Centrifugal force due to fluid particles rotational motion at constant angular velocity says that the magnitude of Centrifugal force caused by the rotational motion along the outside circular line is constructed from those caused by the rotational motions along two different kinds circular lines. One is that caused by the rotational motion along the inside circular line whose rotational center locates at the axis of rotation. And the other is that caused by the rotational motion along the circular line whose circular line touches internally with the outer circular line and locates its rotational center on the inside circular line.
Dynamics of Vapor Bubble Growth and Detachment in a Channel Flow
Authors: Duhar G. , Colin C.
Published: September 2008

The aim of this study is to improve the knowledge of the dynamics of vapor bubbles growing on a wall in a shear flow. Vapor bubbles are created on a hot film probe flushed mounted in the lower wall of a horizontal channel. The film overheat temperature controlled by an anemometer is limited to 20°C to avoid the growth of multiple bubbles. The liquid flow in the channel measured by Particle Image Velocimetry is laminar or turbulent. Bubble growth and detachment in the channel flow are filmed with a high-speed video camera at 2000 frame/second. Image processing allows obtaining the temporal evolutions of the bubble kinematics characteristics: the equivalent radius and the position of the centre of gravity. These data are then used to calculate the bubble growth rate and the forces acting on the bubbles during their growth and after their detachment. After detachment, drag, buoyancy and added mass forces play a dominant role. From the investigation of the bubble trajectories after detachment, the drag coefficient can be determined. When the bubble is attached to the wall capillary forces are dominant. A predictive model for bubble radius at detachment is provided depending on the wall overheat.
Design of Micro Diaphragm Pumps With Active Valves
Authors: Goldschmidtbo¨ing Frank , Doll Alexander , Geipel Andreas , Wischke Martin , Woias Peter
Published: September 2008

This paper deals with the theory, fabrication and characterization of micro diaphragm pumps with active valves. Three types of micropumps with piezoelectric actuation are presented. Special emphasis is given on the accordance of theory and experiment. The theory is based on a lumped-element approach that is reduced to its basics to enable a reasonable accuracy with a minimized set of conceptional parameters. The experimental results fit well to the theory. The fabrication technology of the micropumps comprises of a silicon bulk micromechanics process in combination with a back-end gluing process of piezoelectric PZT-disks (PZT lead-circonat-titanat) to the silicon diaphragms. The micropumps were developed for different applications. The three- and the four-diaphragm micropumps were designed as high performance drivers for an artificial sphincter prosthesis. They show a maximum flowrate of 4 ml/min and a maximum sustainable backpressure of up to 70 kPa. The two-diaphragm micropump was engineered for an implantable drug delivery device and features a pressure independent dosing for backpressures up to 20 kPa.
Prediction of the Aerodynamic Noise Generated by a Centrifugal Fan: Numerical Results and Experimental Validation
Authors: Ballesteros-Tajadura Rafael , Velarde-Sua´rez Sandra , Hurtado-Cruz Juan Pablo , Pereiras-Garci´a Bruno
Published: September 2008

Centrifugal fans are widely used in several applications and, in some cases, the noise generated by these machines has become a serious problem. Usually, the centrifugal fan noise is dominated by tones at the blade passage frequency and its higher harmonics. This is a consequence of the strong interaction between the flow discharged from the impeller and the volute tongue. The purpose of this study is to develop a prediction method for the noise generated by a centrifugal fan. A three-dimensional numerical simulation of the complete unsteady flow on the whole impeller-volute configuration has been carried out using the computational fluid dynamics code FLUENT®. The unsteady forces applied by the fan blades to the fluid are obtained from the data provided by the simulation. The Ffowcs Williams and Hawkings model extension of Lighthill’s analogy predicts the aerodynamic noise generated by the centrifugal fan from these unsteady forces. Also, the noise generated by the fan has been measured experimentally, and the experimental results have been compared to the numerical results in order to validate the aerodynamic noise prediction methodology. A good agreement has been found between the numerical and the experimental results.
LDA Measurements in Rough Surface ZPG Turbulent Boundary layers
Authors: Brzek Brian , Cal Rau´l Bayoa´n , Johansson Gunnar , Castillo Luciano
Published: September 2008

A new set of experiments have been performed in order to study the effects of the upstream conditions and the surface roughness on a zero pressure gradient turbulent boundary layer. In order to properly capture the x-dependence of the single point statistics, consecutive measurements of 11 streamwise locations were performed. These 2-D Laser Doppler Anemometry (LDA) measurements enable us to use the full boundary layer equations in order to calculate the skin friction and determine the boundary layer development which is not possible in the majority of experiments on rough surfaces. It will be shown that for fixed experimental conditions (i.e., fixed upstream wind tunnel speed, trip wire, etc), the velocity deficit profiles collapse for each of the scalings investigated but only the Zagarola/Smits scaling (1998) could collapse all the different experimental conditions into a single curve. In addition, the Reynolds stresses were increasingly affected by the surface roughness as the roughness parameter, k+, increased. Moreover, it was found that the shape of the Reynolds stress profiles was very different throughout the entire boundary layer, particularly the < u2 > component. This is likely the result of the flow becoming more isotropic for increased k+, and will be seen in the anisotropy coefficients. Moreover, increased production of < u2 > and < uv > due to roughness is also seen throughout the entire boundary layer although its overall role in the changing shape of the < u2 > profiles still needs to be determined. The effect of roughness on the boundary layer parameters is also evident and their x-dependence is also shown.
Optimal and Robust Control of Magnetohydrodynamic Channel Flow Instabilities
Authors: Debbagh Karim , Cathalifaud Patricia , Airiau Christophe
Published: September 2008

Active closed-loop control of subcritical and supercritical instabilities amplified in a channel flow submitted to a constant normal magnetic field is investigated. The control is carried out at both the upper and the lower wall by blowing and suction or by a perturbation of the normal magnetic field. A robust formulation (H∞) of the control has been performed to take into account uncertainties coming from the state disturbances and the measurement noise. Optimal and robust dynamic controls have been tested, with full state information or only wall informations. As expected, we found that the closed-loop control modifies the optimal perturbation. However the lift-up mechanisms are still in action. In the supercritical case we found that the control acts almost exclusively on the unstable mode, whose real part becomes negative.
Numerical Analysis of Tip Vortex Cavitation Behavior and Noise on Hydrofoil
Authors: Park Kwangkun , Seol Hanshin , Lee Soogab
Published: September 2008

In this study, tip vortex cavitation behavior and noise are numerically analyzed. Eulerian-Lagrangian approach is used to simulate the tip vortex cavitation on the hydrofoil. In this approach, the flow field and cavitation behavior are computed by Eulerian and Lagrangian point of view, respectively. The vortex flow field is simulated by combining Moore and Saffman’s vortex core radius variation equation with Sculley vortex model. The tip vortex cavitation behavior is analyzed by coupled Rayleigh-Plesset equation and trajectory equation based on Newton’s 2nd law. Kamiirisa’s experimental nuclei data are adopted to produce computational cavitation nuclei population and the nuclei are released in the vortex flow field. The tip vortex cavitation trajectories and radius variations of the nuclei are calculated according to the initial sizes of the nuclei. Noise is analyzed using time dependent cavitation bubble position and radius variation data. When the acting pressure on the nucleus goes down below the vapor pressure, the nucleus grows into a cavitation bubble. And, the cavitation bubble emits very high amplitude noise during collapse stage. This study may become a foundation of the vortex cavitation study.
Wheel Strut Interference
Authors: Christoffersen Lasse M. , Lo¨fdahl Lennart , Jo¨nson Anders
Published: September 2008

To fine tune the aerodynamic properties of road going vehicles the flow along the underbody is of outmost importance. Hence moving ground facilities has been introduced. In full-width mono-belt facilities the test vehicle is most often suspended over the ground plane by a sting system. To mount the wheels, two possibilities exist. The designer of the wind tunnel model is faced with the choice to have the wheels on or off the model. The first option gives the most satisfying boundary conditions from a fluid dynamics point of view, however, the designer will face the problem of creating a frictionless chassis suspension system for the model. The “wheels off” type does not require such complex system but unfortunately creates a non-realistic flow due to the presence of so called wheel struts that carries the wheels. In the present work a numerical study of the flow around a “wheels off” model has been conducted. The study was performed to quantify how the presence of the wheel struts would affect the flow field and hence how this influence flow related measurements made on the model. The work has been done using a commercial CFD-code, running a standard k-epsilon model on a let-dominated mesh, counting roughly 6.5 million cells. As expected the flow field in the vicinity of the wheels is affected due to the extra vorticity introduced by the struts. The modified pressure field alters the drag and of further significance is the influence from the wheel struts on the underbody flow field. It is shown that care must be taken in studies of underbody and later underhood flows, using a “wheels-off” configuration.
LDA Measurements on Rough Turbulent Boundary Layers Subject to Strong Favorable Pressure Gradients
Authors: Cal Rau´l Bayoa´n , Brzek Brian , Johansson Gunnar , Castillo Luciano
Published: September 2008

Laser-Doppler anemometry (LDA) measurements of the mean velocity and Reynolds stresses are carried out on a rough surface favorable pressure gradient (FPG) turbulent boundary layer. These data is compared with smooth FPG turbulent boundary layer data possessing with the same strength of pressure gradient and also with rough zero pressure gradient (ZPG) data. The scales for the mean velocity deficit and Reynolds stresses are obtained through means of equilibrium similarity analysis of the RANS equations [1]. The mean velocity deficit profiles collapse, but to different curves when normalized using the free-stream velocity. The effects of the pressure gradient and roughness are clearly distinguished and separated. However, these effects are removed from the outer flow when the profiles are normalized using the Zagarola and Smits [2] scaling. It is also found that there is a clear effect of the roughness and pressure gradient on the Reynolds stresses. The Reynolds stress profiles augment due to the rough surface. Furthermore, the strength of the pressure gradient imposed of the flow changes the shape of the Reynolds stress profiles especially on the < v2 > and < uv > components. The rough surface influence is mostly noticed on the < u2 > component of the Reynolds stress, where the shape of the profiles change entirely. The boundary layer parameter δ*/δ shows the effects of the roughness and a dependence on the Reynolds number for the smooth FPG case. The pressure parameter, A, describes a development of the turbulent boundary layer and no influence of the roughness is linked with the parameter, k+. The boundary layers grow differently and depict the influence of the studied effects in their development. These measurements are the first of their nature due to the extensive number in downstream locations (12) and the combination of the studied external conditions (i.e., the strength of the pressure gradient and the surface roughness).
Smooth and Rough Turbulent Boundary Layers: A Look at Skin Friction, Pressure Gradient and Roughness
Authors: Newhall Katherine A. , Cal Raul Bayoan , Brzek Brian , Johansson Gunnar , Castillo Luciano
Published: September 2008

The skin friction for a turbulent boundary layer can be measured and calculated in several ways with varying degrees of accuracy. In particular, the methods of the velocity gradient at the wall, the integrated boundary layer equation and the momentum integral equation are evaluated for both smooth and rough surface boundary layers. These methods are compared to the oil film interferometry technique measurements for the case of smooth surface flows. The integrated boundary layer equation is found to be relatively reliable, and the values computed with this technique are used to investigate the effect of increasing external favorable pressure gradient for both smooth and rough surfaces, and increasing roughness parameter for the rough surfaces.