Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 2003"
TL;DR: In this article, a simulation of turbulent cavitation in a Venturi-type section was performed by two-dimensional computations of viscous, compressible, and turbulent cavitating flows.
Abstract: Unsteady cavitation in a Venturi-type section was simulated by two-dimensional computations of viscous, compressible, and turbulent cavitating flows. The numerical model used an implicit finite volume scheme (based on the SIMPLE algorithm) to solve Reynolds-averaged Navier-Stokes equations, associated with a barotropic vapor/liquid state law that strongly links the density variations to the pressure evolution. To simulate turbulence effects on cavitating flows, four different models were implemented (standard $k-\varepsilon$ RNG; modified $k-\varepsilon$ RNG; $k-\omega$ with and without compressibility effects), and numerical results obtained were compared to experimental ones. The standard models $k-\varepsilon$ RNG and $k-\omega$ without compressibility effects lead to a poor description of the self-oscillation behavior of the cavitating flow. To improve numerical simulations by taking into account the influence of the compressibility of the two-phase medium on turbulence, two other models were implemented in the numerical code: a modified $k-\varepsilon$ model and the $k-\omega$ model including compressibility effects. Results obtained concerning void ratio, velocity fields, and cavitation unsteady behavior were found in good agreement with experimental ones. The role of the compressibility effects on turbulent two-phase flow modeling was analyzed, and it seemed to be of primary importance in numerical simulations.
380 citations
TL;DR: In this paper, the impact of inverter load dynamics on fuel cell stack performance and stack lifetime is examined using a dynamic model for the bulk conditions within the stack, as well as a one-dimensional model for detailed mass transport occurring within the electrode of a cell.
Abstract: The effect of inverter ripple current on fuel cell stack performance and stack lifetime remains uncertain. This paper provides a first attempt to examine the impact of inverter load dynamics on the fuel cell. Since reactant utilization is known to impact the mechanical nature of a fuel cell, it is suggested that the varying reactant conditions surrounding the cell govern. at least in part the lifetime of the cells. This paper investigates these conditions through the use of a dynamic model for the bulk conditions within the stack, as well as a one-dimensional model for the detailed mass transport occurring within the electrode of a cell. These two independent modeling approaches are used to verify their respective numerical procedures. in this work, the inverter load is imposed as a boundary condition to the models. Results show the transient behavior of the reactant concentrations within the stack, and of the mass diffusion within the electrode under inverter loads with frequencies between 30 Hz and 1250 Hz.
238 citations
TL;DR: In this paper, optical measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller of industrial design have been performed using particle image velocimetry (PIV) and laser Doppler velocity vector maps as well as bin-resolved LDV data acquired in the midplane between hub and shroud.
Abstract: Detailed optical measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller of industrial design have been performed using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). Results include instantaneous and ensemble averaged PIV velocity vector maps as well as bin-resolved LDV data acquired in the midplane between hub and shroud of the impeller. The flow is surveyed at both design load and at severe off-design conditions. At design load, Q =Q d , the mean field of relative velocity is predominantly vane congruent, showing well-behaved flow with no separation. At quarter-load, Q=0.25Q d , a previously unreported two-channel phenomenon consisting of alternate stalled and unstalled passages was observed, with distinct flow congruence between every second of the six passages. A large recirculation cell blocked the inlet to the stalled passage while a strong relative eddy dominated the remaining parts of the passage. The stall phenomenon was steady, nonrotating and not initiated via the interaction with stationary components
214 citations
TL;DR: In this article, the analytical form of the hydrodynamic force and heat/mass transfer from a particle, bubble or drop is examined critically, and some of the recent computational studies which help strengthen or clarify our knowledge of the complex velocity and temperature fields associated with the momentum and heat transfer processes are also mentioned in a succinct way.
Abstract: Recent advances on the analytical form of the hydrodynamic force and heat/mass transfer from a particle, bubble or drop are examined critically. Also some of the recent computational studies, which help strengthen or clarify our knowledge of the complex velocity and temperature fields associated with the momentum and heat/mass transfer processes are also mentioned in a succinct way. Whenever possible, the processes of energy mass exchange and of momentum exchange from spheres and spheroids are examined simultaneously and any common results and possible analogies between these processes are pointed out. This approach results in a better comprehension of the transport processes, which are very similar in nature, as well as in the better understanding of the theoretical expressions that are currently used to model these processes. Of the various terms that appear in the transient equations, emphasis is given to the history terms, which are lesser known and more difficult to calculate. The origin, form, and method of computation of the history terms are pointed out as well as the effects of various parameters on them
199 citations
TL;DR: In this article, the effect of the subgrid scales has been modeled through a localized dynamic Smagorinsky model implemented in the commercial CFD code FINE/Turbo, and a detailed analysis of the results of LES at design load, Q =Q d, and severe off-design conditions, at quarter-load Q=0.25Q d, is presented.
Abstract: The flow field in a shrouded six-bladed centrifugal pump impeller has been investigated using large eddy simulation (LES). The effect of the subgrid scales has been modeled through a localized dynamic Smagorinsky model implemented in the commercial CFD code FINE/Turbo. A detailed analysis of the results of LES at design load, Q =Q d , and severe off-design conditions, at quarter-load Q=0.25Q d , is presented. At design load LES reveals a well-behaved flow field with no significant separation. At quarter-load significant differences between adjacent impeller passages are revealed. A steady nonrotating stall phenomenon is observed in the entrance of one passage and a relative eddy develops in the remaining part of the passage. The stall unblocks the adjacent passage which exhibits a flow dominated by rotational effects. Velocities predicted by LES and steady-state Reynolds averaged Navier-Stokes (RANS) simulations based on the Baldwin-Lomax and Chien k-e turbulence models are compared with experimental data obtained from particle image velocimetry (PIV)
181 citations
TL;DR: In this paper, a detailed survey of both instantaneous and time-averaged flows is made and a comparison with previous knowledge on similar flows is presented, besides the coherent structures observed in experimental and previous numerical studies, new smaller-scale structures were registered.
Abstract: Flow around a simplified bus is analyzed using large-eddy simulation. At the Reynolds number of 0.21 × 10 6 , based on the model height and the incoming velocity. the flow produces features and aerodynamic forces relevant for the higher (interesting in engineering) Reynolds number. A detailed survey of both instantaneous and time-averaged flows is made and a comparison with previous knowledge on similar flows is presented. Besides the coherent structures observed in experimental and previous numerical studies, new smaller-scale structures were registered here. The mechanisms of formation of flow structures are explained and the difference between instantaneous and time-averaged flow features found in the experimental observations is confirmed. Aerodynamic forces are computed and their time history is used to reveal the characteristic frequencies of the flow motion around the body
142 citations
TL;DR: In this article, the authors developed a three-dimensional finite-volume-based numerical model to simulate pressure-driven liquid flow in microchannels with rectangular prism rough elements on the surfaces.
Abstract: Surface roughness is present in most of the microfluidic devices due to the microfabrication techniques or particle adhesion. It is highly desirable to understand the roughness effect on microscale flow. In this study, we developed a three-dimensional finite-volume-based numerical model to simulate pressure-driven liquid flow in microchannels with rectangular prism rough elements on the surfaces. Both symmetrical and asymmetric roughness element arrangements were considered, and the influence of the roughness on pressure drop was examined
121 citations
TL;DR: In this article, a special test pump with two-dimensional curvature blade geometry was investigated in cavitating and noncavitating conditions using different experimental techniques and a three-dimensional numerical model implemented to study cavitating flows.
Abstract: In the presented study a special test pump with two-dimensional curvature blade geometry was investigated in cavitating and noncavitating conditions using different experimental techniques and a three-dimensional numerical model implemented to study cavitating flows. Experimental and numerical results concerning pump characteristics and performance breakdown were compared at different flow conditions. Appearing types of cavitation and the spatial distribution of vapor structures within the impeller were also analyzed. These results show the ability of the model to simulate the complex three-dimensional development of cavitation in a rotating machinery, and the associated effects on the performance.
108 citations
TL;DR: In this article, the strong interaction of cavitating nozzle flow with the outside jet formation was demonstrated, showing that the cavitating flow is strongly correlated with the formation of the outside jets.
Abstract: The present investigation demonstrates the strong interaction of cavitating nozzle flow with the outside jet formation
100 citations
TL;DR: In this article, the authors investigated flow through fractal-like branching networks using a three-dimensional computational fluid dynamics approach using a previously developed one-dimensional model, with assumptions such as reinitiating boundary layers following each bifurcation, constant thermophysical fluid properties, and negligible minor losses at the bifurlcations.
Abstract: Flow through fractal-like branching networks is investigated using a three-dimensional computational fluid dynamics approach. Results are used to assess the validity of and provide insight for improving, assumptions imposed in a previously developed one-dimensional model. Assumptions in the one-dimensional model include (1) reinitiating boundary layers following each bifurcation, (2) constant thermophysical fluid properties, and (3) negligible minor losses at the bifurcations. No changes to the redevelopment of hydrodynamic boundary layers following a bifurcation are recommended
93 citations
TL;DR: In this paper, the mean velocity and Reynolds stress profiles for smooth and sandgrain rough walls are compared with those for smooth walls, and the results indicate an increase in the boundary layer thickness and integral length scales for the unsanded, painted surface compared to a smooth wall.
Abstract: : Flat-plate turbulent boundary layer measurements have been made on painted surfaces, smoothed by sanding. The measurements were conducted in a closed return water tunnel, over a momentum thickness Reynolds number (Re(theta)) range of 3000 to 16,000, using a two-component laser Doppler velocimeter (LDV). The mean velocity and Reynolds stress profiles are compared with those for smooth and sandgrain rough walls. The results indicate an increase in the boundary layer thickness (d) and the integral length scales for the unsanded, painted surface compared to a smooth wall. More significant increases in these parameters, as well as the skin-friction coefficient (C(f)) were observed for the sandgrain surfaces. The sanded surfaces behave similarly to the smooth wall for these boundary layer parameters. The roughness functions (DeltaU(+)) for the sanded surfaces measured in this study agree within their uncertainty with previous results obtained using towing tank tests and similarity law analysis. The present results indicate that the mean profiles for all of the surfaces collapse well in velocity defect form. The Reynolds stresses also show good collapse in the overlap and outer regions of the boundary layer when normalized with the wall shear stress.
TL;DR: In this paper, the authors derived similarity solutions for several quantities of interest including the cross-stream velocity, Reynolds stress, the dominant turbulent kinetic energy production term, and eddy diffusivities of momentum and heat for axisymmetric and planar turbulent jets, plumes, and wakes.
Abstract: Integral methods are used to derive similarity solutions for several quantities of interest including the cross-stream velocity, Reynolds stress, the dominant turbulent kinetic energy production term, and eddy diffusivities of momentum and heat for axisymmetric and planar turbulent jets, plumes, and wakes. A universal constant is evaluated for axisymmetric and planar plumes
TL;DR: In this article, a spherical model coupled with a bubble motion equation is used to study numerically the dynamics of a nucleus in an imposed flow field, and bubble size and emitted sound versus time are presented for various nuclei sizes and flow field scales in the case of an ideal Rankine vortex.
Abstract: The current study considers the prediction of tip vortex cavitation inception at a fundamental physics based level. Starting form the observation that cavitation inception detection is based on the monitoring of the interaction between bubble nuclei and the flow field, the bubble dynamics is investigated in detail. A spherical model coupled with a bubble motion equation is used to study numerically the dynamics of a nucleus in an imposed flow field. The code provides bubble size and position versus time as well as the resulting pressure at any selected monitoring position. This model is used to conduct a parametric study. Bubble size and emitted sound versus time are presented for various nuclei sizes and flow field scales in the case of an ideal Rankine vortex to which a longitudinal viscous core size diffusion model is imposed. Based on the results, one can deduce cavitation inception with the help of either an optical inception criterion (maximum bubble size larger than a given value) or an acoustical inception criterion (maximum detected noise higher than a given background value)
TL;DR: In this paper, an experimental and numerical study was developed for the unsteady phenomena at off-design conditions of a diffuser pump, and a two-dimensional vortex method was employed to investigate the unstaky flow structure due to the interaction between impeller and diffuser vanes in diffuser pumps at various offdesign conditions.
Abstract: An experimental and numerical study was developed for the unsteady phenomena at off-design conditions of a diffuser pump. Unsteady pressure measurements were made downstream of the impeller, and the pressure fluctuations were analyzed using the ensemble averaging technique as well as the statistical and chaotic time series analysis. The unsteady flow was classified into five ranges as a result of the statistical and chaotic time series analysis. And a two-dimensional vortex method was employed to investigate the unsteady flow structure due to the interaction between impeller and diffuser vanes in a diffuser pump at various off-design conditions
TL;DR: In this paper, the flow of an electrically conducting fluid in a channel with constrictions in the presence of a uniform transverse magnetic field is analyzed and a solution technique for governing magnetohydrodynamic (MHD) equations in primitive variable formulation is developed.
Abstract: An analysis is made of the flow of an electrically conducting fluid in a channel with constrictions in the presence of a uniform transverse magnetic field. A solution technique for governing magnetohydrodynamic (MHD) equations in primitive variable formulation is developed. A coordinate stretching is used to map the long irregular geometry into a finite computational domain. The governing equations are discretized using finite difference approximations and the well-known staggered grid of Harlow and Welch is used. Pressure Poisson equation and pressure-velocity correction formulas are derived and solved numerically
TL;DR: In this paper, a TVD MacCormack's scheme employing a locally homogeneous model of compressible gas-liquid two-phase media was applied to analyze above cavity flows.
Abstract: 2-D unsteady cavity flows through hydrofoils in cascade which is the most fundamental element of turbomachinery are numerically calculated. In particular, attention was paid to instability phenomena of the sheet cavity in transient cavitation condition and the mechanism of break-off phenomenon was examined. A TVD MacCormack's scheme employing a locally homogeneous model of compressible gas-liquid two-phase media was applied to analyze above cavity flows. The present method permits us to treat the whole cavitating/noncavitating unsteady flow field. By analyzing numerical results in detail, it became clear that there are at least two mechanisms in the break-off phenomena of sheet cavity; one is that re-entrant jets play a dominant role in such a break-off phenomenon, and the other is that pressure waves propagating inside the cavity bring about an another type of break-off phenomenon accompanied with cavity surface waves.
TL;DR: The use of dense gases in many technological fields requires modern fluid dynamic solvers capable of treating the thermodynamic regions where the ideal gas approximation does not apply as mentioned in this paper, and in some high molecular fluids, nonclassical fluid dynamic effects appearing in those regions could be exploited to obtain more efficient processes.
Abstract: The use of dense gases in many technological fields requires modern fluid dynamic solvers capable of treating the thermodynamic regions where the ideal gas approximation does not apply. Moreover, in some high molecular fluids, nonclassical fluid dynamic effects appearing in those regions could be exploited to obtain more efficient processes. This work presents the procedures for obtaining nonconventional thermodynamic properties needed by up to date computer flow solvers. Complex equations of state for pure fluids and mixtures are treated. Validation of sound speed estimates and calculations of the fundamental derivative of gas dynamics Γ are shown for several fluids and particularly for Siloxanes, a class of fluids that can be used as working media in high-temperature organic Rankine cycles. Some of these fluids have negative Γ regions if thermodynamic properties are calculated with the implemented modified Peng-Robinson thermodynamic model. Results of flow simulations of one-dimensional channel and two-dimensional turbine cascades will be presented in upcoming publications
TL;DR: In this article, the structure of the jet flow and its regimes as a function of jet speed and free-jet length were measured in the developing shear layer of a large-size plunging jet (d_1 = 25 mm).
Abstract: Circular plunging jets were studied by both void fraction and acoustic techniques. There were two aims: to measure the structure of the jet flow and its regimes as a function of jet speed and free-jet length; and to develop and validate the acoustic measurement technique in the developing flow. Void fractions and bubble count rates were measured in the developing shear layer of a large-size plunging jet (d_1 = 25 mm). The data compared well with a solution of an advective diffusion equation and showed an increased air entrainment rate with increasing free-jet length for x_1 /d_1 =/ < 12. The acoustic data were processed by a novel technique to extract both bubble count and bubble size data. Three plunging jet flow regimes were noted. Near inception, acoustic pulses are isolated and indicate individual bubble entrainment as observable visually. Above a characteristic jet velocity, the number of the bubble pulses increases sharply although bubbles are still produced intermittently. At higher velocities, bubble production becomes quasi-continuous. The study suggests that an acoustic technique calibrated through detailed laboratory measurements can provide useful, absolute data in high-void fraction flows. The robust acoustic sensor can then be used in hostile industrial or environmental flows where more delicate instruments are impractical.
TL;DR: In this paper, the performance of a centrifugal compressor is analyzed and discussed in order to understand the performance behavior of the compressor exposed to different inlet configurations, such as a straight pipe with constant cross-sectional area and a 90-deg curved pipe with nozzle shape.
Abstract: The performance of centrifugal compressors can be seriously degraded by inlet flow distortions that result from an unsatisfactory inlet configuration. In this present work, the flow is numerically simulated and the flow details are analyzed and discussed in order to understand the performance behavior of the compressor exposed to different inlet configurations. In a previous work, complementary to this present work, experimental tests were carried out for the comparison of a centrifugal compressor stage performance with two different inlet configurations: one of which was a straight pipe with constant cross-sectional area and the other a 90-deg curved pipe with nozzle shape. Steady-state compressor stage simulation including the impeller and diffuser with three different inlets has been carried out to investigate the influence of each inlet type on the compressor performance. The three different inlet systems included a proposed and improved inlet model. The flow from the bend inlet is not axisymmetric in the circumferential and radial distortion, thus the diffuser and the impeller are modeled with fully 360-deg passages
TL;DR: In this paper, the entrainment characteristics of circular and non-circular jets were investigated, and the authors showed that the flow is incompressible and isothermal at a jet Reynolds number of 7200.
Abstract: The present work deals with the experimental investigation of entrainment characteristics of confined/semiconfined circular and noncircular jets. The jet fluid, after issuing out of a nozzle of circular or noncircular cross section, enters a circular mixing tube of larger area, and during this process it entrains some ambient fluid into the mixing tube. The flow is incompressible and isothermal at a jet Reynolds number of 7200
TL;DR: In this article, a procedure was developed to predict the effects of roughness and Reynolds number on the change in efficiency from a model or baseline to a prototype pump (efficiency scaling).
Abstract: A procedure has been developed to predict the effects of roughness and Reynolds number on the change in efficiency from a model or baseline to a prototype pump (efficiency scaling). The analysis of individual losses takes into account different roughnesses of impeller, diffuser/volute, impeller side disks, and casing walls in the impeller side rooms. The method also allows to predict the effect of roughness and Reynolds number on the hydraulic efficiency. The calculations are based on physical models but the weighting of impeller versus diffuser/volute roughness and the fraction of scalable losses within impeller and diffuser/volute are determined empirically from the analysis of tests with industrial pumps. The procedure includes all flow regimes from laminar to turbulent and from hydraulically smooth to fully rough
TL;DR: In this article, particle image velocimetry (PIV) was used to measure air velocities through a high solidity radial flow fan utilized as an automotive vented brake rotor.
Abstract: Particle image velocimetry (PIV) was used to measure air velocities through a high solidity radial flow fan utilized as an automotive vented brake rotor. A brake rotor is a somewhat unusual fan in that its sole purpose is not to pump air but to dissipate thermal energy, it has no conventional inlet or outlet housing and it has a continuously varying rotational speed. For three typical rotational speeds, the flow characteristics were captured at the inlet and exit of the rotor, as well as internally through the cooling passages. Inlet measurements showed a swirling entry, flow condition with significant misalignment of flow onto the vanes. As a result large regions of flow separation were found in the internal vane-to-vane passages on the suction side surfaces, which would lead to poor heat transfer conditions. The main flow exiting the rotor consisted of a series of jets corresponding to the individual rotor passages
TL;DR: In this paper, the lateral flow fields in four subchannels of a model rod bundle fuel assembly are experimentally measured using particle image velocimetry, where split-vane pairs are located on the downstream edge of the support grids and generate swirling flow.
Abstract: Lateral flow fields in four subchannels of a model rod bundle fuel assembly are experimentally measured using particle image velocimetry. Vanes (split-vane pairs) are located on the downstream edge of the support grids in the rod bundle fuel assembly and generate swirling flow. Measurements are acquired at a nominal Reynolds number of 28,000 and for seven streamwise locations ranging from 1.4 to 17.0 hydraulic diameters downstream of the grid. The streamwise development of the lateral flow field is divided into two regions based on the lateral flow structure. In Region I, multiple vortices are present in the flow field and vortex interactions occur. Either a single circular vortex or a hairpin shaped flow structure is formed in Region II. Lateral kinetic energy, maximum lateral velocity, centroid of vorticity, radial profiles of azimuthal velocity, and angular momentum are employed as measures of the streamwise development of the lateral flow field. The particle image velocimetry measurements of the present study are compared with laser Doppler velocimetry measurements taken for the identical support grids and flow condition.
TL;DR: In this article, Davis et al. discuss the role of fingering as an archetype for growth patterns in vascular fluid dynamics, including blood flow in arteries and veins and open shear flow instabilities.
Abstract: Preface 1. Interfacial fluid dynamics Stephen Davis 2. Viscous fingering as an archetype for growth patterns Yves Couder 3. Blood flow in arteries and veins Tim Pedley 4. Open shear flow instabilities Patrick Huerre 5. Turbulence Javier Jimenez 6. Convection in the environment Paul Linden 7. Reflections on magnetohydrodynamics Keith Moffatt 8. Solidification of fluids Grae Worster 9. Geological fluid mechanics Herbert Huppert 10. The dynamic ocean Chris Garrett 11. On global-scale atmospheric and oceanic circulations Michael McIntyre Index.
TL;DR: In this article, the authors analyzed and characterised the irreversibility of the ejector's internal processes in an effort to improve the understanding of the making of its overall performance, based on entropy production methodology.
Abstract: The present study analyzes and characterizes the irreversibility of the ejector's internal processes in an effort to improve the understanding of the making of its overall performance. The analysis presented is based on entropy production methodology. Since entropy production is equivalent to performance losses, minimizing entropy production could serve as a tool for performance optimization. The three main internal processes forming sources of ejector irreversibility are mixing, kinetic energy losses, and normal shock wave. Comparison of these with those of an ideal mixing process, an ideal turbine-compressor system and stagnation conditions (of the flow after mixing) provides the benchmarks against which the actual overall performance is measured. By identifying the sources of irreversibility, the analysis provides a diagnostic tool for performance improvements. While irreversibility due to mixing can be eliminated by appropriate choice of gas and/or inlet conditions and an appropriate adjustable throat can eliminate losses associated with normal shock wave-kinetic energy losses can only be reduced but not totally eliminated
TL;DR: In this article, a sensitivity analysis is done for turbulent cavitating flows using a pressure-based Navier-Stokes solver coupled with a phase volume fraction transport model and non-equilibrium k-e turbulence closure.
Abstract: A sensitivity analysis is done for turbulent cavitating flows using a pressure -based Navier-Stokes solver coupled with a phase volume fraction transport model and non-equilibrium k-e turbulence closure. Four modeling parameters are adopted for evaluation, namely, Ce1 and Ce2, which directly influences the production and dissipation of turbulence kinetic energy, and Cdest and Cprod, which regulate the evaporation and condensation of the phases. Response surface methodology along with design of experiments is used for the sensitivity studies. The difference between the computational and experimental results is used to judge the model fidelity. Under non-cavitating conditions, the best selections of Ce1 and Ce2, exhibit a linear combination with multiple optima. Using this information, cavitating flows around an axi -symmetric geometry with a hemispherical fore-body and the NACA66(MOD) airfoil are assessed. Analysis of the cavitating model shows that the favorable combinations of Cdest and Cprod, are inversely proportional to each other for the geometries considered. A set of cavitation numbers is selected for each of the geometries to demonstrate the predictive capability of the present modeling approach for attached, turbulent cavitating flows.
TL;DR: In this paper, the effect of wake passing frequency on the boundary layer transition along the concave surface of a curved plate wider a zero longitudinal pressure gradient was investigated using conventional and wavelet-based methods.
Abstract: Detailed experimental and theoretical investigations were carried out to study the effect of unsteady wake passing frequency on the boundary layer transition along the concave surface of a curved plate wider a zero longitudinal pressure gradient. Periodic unsteady flow with different passing frequencies is generated utilizing an unsteady flow research facility with a rotating cascade of rods positioned upstream of the curved plate. Extensive unsteady boundary layer measurements are carried out. The data are analyzed using conventional and wavelet-based methods. Local time scales are defined as those of the most energetic fluctuations. and are calculated from wavelet transforms of the velocity signals. The dominant time scales are mapped as functions of the distance to the plate the downstream location, and the phase relative to the wake-passing. Furthermore, conditional sampling is applied laminar and turbulent time scales are calculated and the effects of wake passing frequency on these scales are shown
TL;DR: In this article, the unsteady viscous flow fields of a cross-flow fan are computed by time-accurately solving the two-dimensional incompressible Navier-Stokes equations with the unstructured triangular mesh solver algorithms.
Abstract: The unsteady viscous flow fields of a cross-flow fan are computed by time-accurately solving the two-dimensional incompressible Navier-Stokes equations with the unstructured triangular mesh solver algorithms. Based on pressure fluctuation data acquired at the surfaces of 35 rotating blades and stabilizer, acoustic pressures are predicted by the Ffowcs Williams-Hawkings equation. The aerodynamic noise sources of the cross-flow fan are also identified by correlating the acoustic pressure fluctuations with the unsteady flow characteristics during one revolution of the impeller. The present method is applied to the uniform and random pitch fans to investigate their performance and aeroacoustic noise characteristics, especially the frequency modulation of the tonal noise at the blade passing frequency (BPF).
TL;DR: In this paper, the influence of the shape of the leading edge and its sharpening on the cavitating behavior of an inducer is analyzed, from experimental results, using a methodology developed at LEMFI.
Abstract: We analyze, from experimental results, the influence of the shape of the leading edge and its sharpening on the cavitating behavior of an inducer. The studied inducer is designed according to a methodology developed at LEMFI. Successive cutting and sharpening (four cuts, which modify up to 20 percent of the blade chord at the tip), were made to modify the shape of the leading edge. For the various geometries, the experimental results obtained on the LEMFI test rig are presented as follows. Noncavitating Regime.- Overall performances at 1450 rpm. Cavitating Regime.- (1) The development of the cavitation versus the cavitation number, (2) the description of the various cavitation pictures, and (3) the pressure fluctuations measured at the wall at 150 mm downstream of the trailing edge for various flow: rates and inlet pressures. The CFD simulations carried out under CFX-Blade Gen + on this range of inducers are presented to explain certain aspects observed