Experimental and Numerical Investigation of the Unsteady Flow Field and Tone Generation in an Isolated Centrifugal Fan Impeller

2011 ◽  
Author(s):  
Daniel Wolfram ◽  
Thomas H. Carolus
Keyword(s):  
Unsteady Flow ◽  
Numerical Investigation ◽  
Vortex Core ◽  
Large Range ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Centrifugal Fan ◽  
Helical Vortex ◽  
The One ◽  
Tone Generation

In spite of low circumferential Mach number the sound of isolated centrifugal fan impellers is sometimes dominated by distinctive tones at blade passing frequency (BPF) and integer multiples. This paper reports on an experimental and numerical investigation intended to unveil the tone generating mechanism. The sound spectra from three impellers operating at a large range of speed were measured and decomposed into Strouhal and Helmholtz number dependent functions. This led to the preliminary conclusion that the BPF related tones are exclusively flow-induced. Based on hot-wire and blade pressure fluctuation measurements and a subsequent correlation analysis, coherent flow structures different from the one associated with the principal azimuthal flow pattern due to the blades were detected. Eventually, numerical three-dimensional unsteady flow simulation and experimental flow visualization revealed an inlet vortex. It takes on a helical form, with the vortex core slowly varying its position with respect to the impeller center. As the blades cut through that quasi-stationary helical vortex they encounter blade force fluctuations producing the BPF tones. The slow spin of the vortex core and the slow variation of vortex strength were identified as the reason for the amplitude modulation of the BPF tone.

Assessment of Unsteady Flows in Turbines

1992 ◽  
Vol 114 (1) ◽  
pp. 79-90 ◽  
Author(s):  
O. P. Sharma ◽  
G. F. Pickett ◽  
R. H. Ni
Keyword(s):  
Unsteady Flow ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Experimental Investigations ◽  
Flow Parameters ◽  
Research Activities ◽  
Flow Features ◽  
Computational Fluid Dynamics Cfd ◽  
Turbine Design ◽  
The Impact

The impacts of unsteady flow research activities on flow simulation methods used in the turbine design process are assessed. Results from experimental investigations that identify the impact of periodic unsteadiness on the time-averaged flows in turbines and results from numerical simulations obtained by using three-dimensional unsteady Computational Fluid Dynamics (CFD) codes indicate that some of the unsteady flow features can be fairly accurately predicted. Flow parameters that can be modeled with existing steady CFD codes are distinguished from those that require unsteady codes.

Modeling Hydroplaning and Effects of Pavement Microtexture

2005 ◽  
Vol 1905 (1) ◽  
pp. 166-176 ◽  
Author(s):  
G. P. Ong ◽  
T. F. Fwa ◽  
J. Guo
Keyword(s):  
Three Dimensional ◽  
Flow Simulation ◽  
Experimental Results ◽  
Tire Pressure ◽  
Finite Volume Model ◽  
Proposed Model ◽  
Loss Of Contact ◽  
The One ◽  
Theoretical Considerations ◽  
Good Agreement

Hydroplaning on wet pavement occurs when a vehicle reaches a critical speed and causes a loss of contact between its tires and the pavement surface. This paper presents the development of a three-dimensional finite volume model that simulates the hydroplaning phenomenon. The theoretical considerations of the flow simulation model are described. The simulation results are in good agreement with the experimental results in the literature and with those obtained by the well-known hydroplaning equation of the National Aeronautics and Space Administration (NASA). The tire pressure–hydroplaning speed relationship predicted by the model is found to match well the one obtained with the NASA hydroplaning equation. Analyses of the results of the present study indicate that pavement microtexture in the 0.2- to 0.5-mm range can delay hydroplaning (i.e., raise the speed at which hydroplaning occurs). The paper also shows that the NASA hydroplaning equation provides a conservative estimate of the hydroplaning speed. The analyses in the present study indicate that when the microtexture of the pavement is considered, the hydroplaning speed predicted by the proposed model deviates from the speed predicted by the smooth surface relationship represented by the NASA hydroplaning equation. The discrepancies in hydroplaning speed are about 1% for a 0.1-mm microtexture depth and 22% for a 0.5-mm microtexture depth. The validity of the proposed model was verified by a check of the computed friction coefficient against the experimental results reported in the literature for pavement surfaces with known microtexture depths.

Numerical Investigation of the Unsteady Flow at High Reynolds Number Over a Marine Riser With Helical Strakes

2006 ◽  
Author(s):  
Antonio Pinto ◽  
Riccardo Broglia ◽  
Andrea Di Mascio ◽  
Emilio F. Campana ◽  
Pierpaolo Rocco
Keyword(s):  
Fluid Dynamics ◽  
Unsteady Flow ◽  
Numerical Investigation ◽  
Three Dimensional ◽  
Numerical Code ◽  
Three Dimensional Model ◽  
Analysis Phase ◽  
Helical Strakes ◽  
Advanced Analysis ◽  
High Reynolds

Prediction of Vortex-Induced Vibrations (VIV) is one of the main topics in the design of deepwater risers. The understanding and modelling of the complex fluid-structure interaction requires advanced analysis techniques coupling, in a correct manner, both structural and fluid dynamics aspects. This study aims to develop, optimise and calibrate a numerical code to provide reliable results within a reasonable analysis timeframe and without, or very limited, need of experimental verification. For this purpose, the unsteady Reynolds Average Navier-Stokes (RANS) code χnavis is applied to solve a typical riser VIV problem and compute the three-dimensional riser-fluid dynamics interaction. During a preliminary analysis phase, the two-dimensional (2-D) flow past (i) a bare circular cylinder and (ii) a straked riser at high Reynolds numbers is simulated (different incidences flow/strake vanes are analysed). Numerical results are validated and calibrated against published test data. The core analysis phase is then focused on the numerical investigation of the unsteady flow over a three-dimensional (3-D) helical strake. In this phase, the three-dimensional flow field, turbulent structures and response frequency patterns are analysed. Spectral analysis of data is performed to identify carrier frequencies deemed to be critical due to the induced vibration of the whole structure, and helical strakes efficiency in reducing the riser vibrations is also addressed. Finally, comparison between numerical and experimental results shows that the complexity of a three-dimensional model is indeed compensated by a significantly improved accuracy of the obtained results.

scholarly journals Effect of Nozzle Confinement in the Axial Swirler

2019 ◽  
Vol 196 ◽  
pp. 00032
Author(s):  
Roman Yusupov ◽  
Ivan Litvinov ◽  
Sergey Shtork
Keyword(s):  
Unsteady Flow ◽  
Strouhal Number ◽  
Vortex Core ◽  
Recirculation Zone ◽  
Averaging Method ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Secondary Vortex ◽  
Precessing Vortex Core ◽  
Swirl Parameter

This work is devoted to the study of unsteady flow with the precessing vortex core (PVC) formed at the exit of a compact vane swirler with varying vanes angle and nozzles diameters. Amplitude-frequency characteristics of the PVC were obtained using two microphones. The modified Strouhal number dependence have showed a good generalization of the data for all nozzle diameters. The averaged and phase-averaged distributions of three components of velocity have been measured via the LDA system. The increasing the recirculation zone at increasing nozzle diameter for the swirl parameter Sg=0.53 and Re=1.5·104 was detected. The degeneration of PVC was detected for all studied nozzle diameters D = 30, 40, 50 mm. In case of smallest diameter D = 30 mm the PVC ceases to be periodic due to the absence of a recirculation zone. The three-dimensional structure of the PVC is reconstructed by the phase averaging method and visualized using the Q-criterion. Formation of the shifted recirculation zone, outer secondary vortex (OSV) and inner secondary vortex (ISV) is observed.

scholarly journals Direct Numerical Simulation of Gas–Particle Flows with Particle–Wall Collisions Using the Immersed Boundary Method

2018 ◽  
Vol 8 (12) ◽  
pp. 2387 ◽  
Author(s):  
Yusuke Mizuno ◽  
Shun Takahashi ◽  
Kota Fukuda ◽  
Shigeru Obayashi
Keyword(s):  
Immersed Boundary Method ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Navier Stokes ◽  
Immersed Boundary ◽  
Navier Stokes Equation ◽  
Level Set Function ◽  
Boundary Method ◽  
The One ◽  
Energy And Momentum

We investigated particulate flows by coupling simulations of the three-dimensional incompressible Navier–Stokes equation with the immersed boundary method (IBM). The results obtained from the two-way coupled simulation were compared with those of the one-way simulation, which is generally applied for clarifying the particle kinematics in industry. In the present flow simulation, the IBM was solved using a ghost–cell approach and the particles and walls were defined by a level set function. Using proposed algorithms, particle–particle and particle–wall collisions were implemented simply; the subsequent coupling simulations were conducted stably. Additionally, the wake structures of the moving, colliding and rebounding particles were comprehensively compared with previous numerical and experimental results. In simulations of 50, 100, 200 and 500 particles, particle–wall collisions were more frequent in the one–way scheme than in the two-way scheme. This difference was linked to differences in losses in energy and momentum.

Analysis of Unsteady Flow Around Airfoil of a HAWT by Vortex Method

2003 ◽  
Author(s):  
Hiroshi Imamura ◽  
Daisuke Takezaki ◽  
Masahiro Kawai ◽  
Yutaka Hasegawa ◽  
Koji Kikuyama
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Deterministic Model ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Simple Algorithm ◽  
Vortex Method ◽  
Vortex Methods ◽  
Outer Flow ◽  
Vortex Element

Vortex methods have features such as relatively simple algorithm, no grid-generation in flow field and lagrangian scheme which traces each vortex element concentrated in a tiny region. It is considered that the vortex methods are effective tools for the analysis of three-dimensional, incompressible and unsteady outer flow such as flow around wind turbines. Recently, vortex methods are employed as engineering tools for three-dimensional unsteady flow. In a flow simulation by vortex methods, accuracy of simulation depends chiefly on the vortex creation model on the wall and the viscous diffusion effects. However, it seems that the deterministic model to introduce the vortex element created on the wall into flow field has not yet been accomplished. In this paper, an introduction model of vortex elements from the wall into flow field is proposed. This model is based on the analogy of the consideration of boundary-layer. In this model, intensity of vortex elements created on the wall is determined by applying both no-through and no-slip boundary conditions and the diffusion height of each element created on the wall is determined dynamically. To investigate the applicability of the model, proposed method is applied to flow around impulsively started airfoil section.

Transonic and Supersonic Inviscid Flow Equations in 3-D Eccentric Nozzles

2002 ◽  
Author(s):  
Ali Reza Mazaheri ◽  
Homayoon Emdad ◽  
Goodarz Ahmadi
Keyword(s):  
Three Dimensional ◽  
Flow Simulation ◽  
Inviscid Flow ◽  
Analytic Solutions ◽  
Inviscid Flows ◽  
Flow Equations ◽  
The Stability ◽  
The One ◽  
Volume Method ◽  
Steady And Unsteady Flows

Three dimensional unsteady inviscid flows in convergent-divergent nozzles is of importance in understanding the stability of rockets and jet propulsion. A computer program for evaluating unsteady inviscid flow conditions in three-dimensional eccentric as well as concentric nozzles is developed. The program uses the cell-centered finite-volume method based on Roe’s approximate Riemann solver scheme. The flow simulation results in concentric circular nozzles are compared with the one-dimensional analytic solutions and the accuracy of the computation model is verified. The results for steady and unsteady flows through eccentric and concentric convergent-divergent nozzles are then presented. A range of exit to throat areas, pressure ratios, and inlet Mach number are considered.

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