Three dimensional numerical investigation of unsteady flow parameters in partial admission turbine

2014 ◽  
pp. 313-316
Keyword(s):  
Unsteady Flow ◽  
Numerical Investigation ◽  
Three Dimensional ◽  
Flow Parameters ◽  
Partial Admission

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.

Non-Equilibrium Relaxing Gas Flow Behind Three Dimensional Unsteady Curved Shock Wave

1980 ◽  
Vol 35 (11) ◽  
pp. 1166-1170
Author(s):  
V. D. Sharma ◽  
Radhe Shyam
Keyword(s):  
Shock Wave ◽  
Unsteady Flow ◽  
Gas Flow ◽  
Three Dimensional ◽  
Flow Conditions ◽  
Shock Surface ◽  
Flow Parameters ◽  
Upstream Flow ◽  
Relaxing Gas ◽  
Non Equilibrium

Abstract A shock wave is assumed to exist in a three-dimensional unsteady flow of a relaxing gas. The variation of flow parameters at any point behind the shock surface is determined in terms of the shock geometry and the upstream flow conditions. The expressions for the vorticity and the curvature of a streak line at the rear of the shock surface are also determined in terms of the known quantities.

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.

Computation of unsteady flow through steam turbine blade rows at partial admission

1997 ◽  
Vol 211 (3) ◽  
pp. 197-205 ◽  
Author(s):  
L He
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Stokes Equations ◽  
Computational Study ◽  
Guide Vane ◽  
Three Dimensional ◽  
Admission Rate ◽  
Inlet Guide Vane ◽  
Flow Equations ◽  
Partial Admission

Partial admission in the steam turbine is associated with strong unsteady flow effects on aerodynamic performance. This paper presents a first-of-its-kind computational study of the problem. The unsteady flow field in multiple blade passages and multiple blade rows is governed by the quasi three-dimensional unsteady Navier-Stokes equations, closed by a mixing-length turbulence model. The partial admission is introduced by blocking one segmental arc (or several segmental arcs) of the inlet guide vane of the first stage. The flow equations are solved by using a time-dependent finite volume method. The calculated unsteady force on rotor blades for a turbine stage at partial admission compares well with the corresponding experimental data. The present results show that a cyclic pumping and sucking phenomenon occurs in the rotor blade row of the first stage, resulting in large unsteady loading and marked mixing loss. For a single stage at a given admission rate, a blocking arrangement with two flow segments is shown to be much more detrimental than one arc of admission, because of the extra mixing loss. The results for a two-stage case, however, suggest that the decaying rate of circumferential non-uniformities could be far more important for performance. For this reason, an enhanced mixing loss in the first stage might be beneficial to the overall efficiency of a multistage turbine.

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.

Numerical Study of Unsteady Flow Phenomena in a Partial Admission Axial Steam Turbine

2008 ◽  
Author(s):  
Narmin B. Hushmandi ◽  
Jiasen Hu ◽  
Jens Fridh ◽  
Torsten H. Fransson
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Surface Pressure ◽  
Cross Sections ◽  
Static Pressure ◽  
Three Dimensional ◽  
Rotor Blades ◽  
Strong Mixing ◽  
Partial Admission ◽  
Flow Phenomena

This paper presents a numerical investigation of unsteady flow phenomena in a two-stage partial admission axial steam turbine. Results from unsteady three-dimensional computations are analyzed and compared with the available experimental data. Partial admission in the present study is introduced into the model by blocking only one segmental arc of the inlet guide vanes. Blocking only one segment (which corresponds to the experimental setup) makes the model unsymmetrical; therefore it is necessary to model the whole annulus of the turbine. The first stage rotor blades experience large static pressure change on their surface while passing the blocked channel. The effect of blockage on the rotor blades’ surface pressure can be seen few passages around the blocked channel. Strong changes of the blades’ surface pressure impose large unsteady forces on the blades of first stage rotor row. The circumferential static pressure plots at different cross sections along the domain indicate how the non-uniformity propagates in the domain. A peak pressure drop is seen at the cross section downstream of the first stage stator row. At further downstream cross sections, the static pressure becomes more evenly distributed. Entropy generation is higher behind the blockage due to the strong mixing and other loss mechanisms involved with partial admission. Analysis of the entropy plots at different cross sections indicates that the peak entropy moves in a tangential direction while traveling to the downstream stages. Comparisons of the unsteady three-dimensional numerical results and the experimental measurement data show good agreement in tendency. However some differences are seen in the absolute values especially behind the blockage.

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