scholarly journals Loss and Deviation in Windmilling Fans

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Ewan J. Gunn ◽  
Cesare A. Hall
Keyword(s):  
Control Volume ◽  
Three Dimensional ◽  
Flow Coefficient ◽  
High Loss ◽  
Pressure Surface ◽  
Blade Row ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Transonic Fan ◽  
Cruise Flight

For an unpowered turbofan in flight, the airflow through the engine causes the fan to freewheel. This paper considers the flow field through a fan operating in this mode, with emphasis on the effects of blade row losses and deviation. A control volume analysis is used to show that windmilling fans operate at a fixed flow coefficient which depends on the blade metal and deviation angles, while the blade row losses are shown to determine the fan mass flow rate. Experimental and numerical results are used to understand how the loss and deviation differ from the design condition due to the flow physics encountered at windmill. Results are presented from an experimental study of a windmilling low-speed rig fan, including detailed area traverses downstream of the rotor and stator. Three-dimensional computational fluid dynamics (CFD) calculations of the fan rig and a representative transonic fan windmilling at a cruise flight condition have also been completed. The rig test results confirm that in the windmilling condition, the flow through the fan stator separates from the pressure surface over most of the span. This generates high loss, and the resulting blockage changes the rotor work profile leading to modified rotational speed. In the engine fan rotor, a vortex forms at the pressure surface near the tip and further loss results from a hub separation caused by blockage from the downstream core and splitter.

Experimental Study of Three-Dimensional Flow in an Axial Compressor Stage

1986 ◽  
Author(s):  
Vaclav Cyrus
Keyword(s):  
Three Dimensional ◽  
Axial Compressor ◽  
Loss Coefficient ◽  
Flow Coefficient ◽  
Compressor Stage ◽  
Three Dimensional Flow ◽  
High Loss ◽  
Dimensional Flow ◽  
Blade Row ◽  
Stator Blade

A detailed investigation of three-dimensional flow was carried out in a low speed axial compressor stage with aspect ratio of 2. Data were obtained over a range of flow coefficient. The origin of large high loss regions in each blade row was found by means of a diffusion factor. The loss coefficient of rotor and stator blade rows was established on the basis of both rotating and stationary pressure probes. The predicted rotor and stator loss coefficient was compared with experiment.

scholarly journals Numerical Calculation of Flow for Cascade With Tip Clearance

1994 ◽  
Author(s):  
Shimpei Mizuki ◽  
Hoshio Tsujita
Keyword(s):  
Three Dimensional ◽  
Tip Clearance ◽  
Turbine Cascade ◽  
Governing Equations ◽  
Tensor Form ◽  
Pressure Surface ◽  
Rear Part ◽  
Blade Tip ◽  
Flow Through ◽  
Blade Tip Geometry

Three-dimensional incompressible turbulent flow within a linear turbine cascade with tip clearance is analyzed numerically. The governing equations involving the standard k-ε model are solved in the physical component tensor form with a boundary-fitted coordinate system. In the analysis, the blade tip geometry is treated accurately in order to predict the flow through the tip clearance in detail when the blades have large thicknesses. Although the number of grids employed in the present study is not enough because of the limitation of computer storage memory, the computed results show good agreements with the experimental results. Moreover, the results clearly exhibit the locus of minimum pressure on the rear part of the pressure surface at the blade tip.

scholarly journals A computational investigation of the hydrodynamics of the Badush dam in northern Iraq

2018 ◽  
Vol 240 ◽  
pp. 04009
Author(s):  
Younis Saida Saeedrashed ◽  
Ali Cemal Benim
Keyword(s):  
Three Dimensional ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Dam Failure ◽  
Northern Iraq ◽  
Digital Elevation ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Elevation Model ◽  
Bottom Outlets

A computational analysis of the hydrodynamics of the Badush dam in Iraq is presented, which is planned to be reconstructed as a repulse dam, to prevent the Mosul city, in case of a failure of the Mosul dam. Computational Fluid Dynamics (CFD) is applied in combination with Geometric Information System (GIS) and Digital Elevation Model (DEM). In the first part of the study, a hydrologic study of a possible Mosul dam failure is performed, predicting the important parameters for a possible flooding of Mosul city. Here, a two-dimensional, depth-averaged shallow water equations are used to formulate the flow. Based on GIS and DEM, the required reservoir size and the water level of the Badush dam are predicted, for its acting as a repulse dam. Subsequently, a computational model of the reconstructed Badush dam is developed, combining the proposed construction with the local geographic topology to achieve a perfect fit. Finally, the water flow through the bottom outlets and stilling basin of the proposed dam is calculated by an unsteady, three-dimensional CFD analysis of the turbulent, free-surface flow. The CFD model is validated by comparing the predictions with measurements obtained on a physical model, where a quite satisfactory agreement is observed.

Excess Streamwise Vorticity and Its Role in Secondary Flow

1987 ◽  
Vol 201 (6) ◽  
pp. 413-420 ◽  
Author(s):  
P W James
Keyword(s):  
Secondary Flow ◽  
Gas Turbines ◽  
Three Dimensional ◽  
Point Of View ◽  
Streamwise Vorticity ◽  
Three Dimensional Flow ◽  
Approximate Methods ◽  
Blade Row ◽  
Flow Through ◽  
Loss Term

The purpose of this paper is, firstly, to show how the concept of excess secondary vorticity arises naturally from attempts to recover three-dimensional flow details lost in passage-averaging the equations governing the flow through gas turbines. An equation for the growth of excess streamwise vorticity is then derived. This equation, which allows for streamwise entropy gradients through a prescribed loss term, could be integrated numerically through a blade-row to provide the excess vorticity at the exit to a blade-row. The second part of the paper concentrates on the approximate methods of Smith (1) and Came and Marsh (2) for estimating this quantity and demonstrates their relationship to each other and to the concept of excess streamwise vorticity. Finally the relevance of the results to the design of blading for gas turbines, from the point of view of secondary flow, is discussed.

Three Dimensional Numerical Simulation of Flow Field Inside a Reversible Pumping Station With Symmetric Aerofoil Blade

2008 ◽  
Author(s):  
Li Cheng ◽  
Chao Liu ◽  
Jiren Zhou ◽  
Fangping Tang ◽  
Yan Jin
Keyword(s):  
Flow Field ◽  
Control Volume ◽  
Three Dimensional ◽  
Flow Coefficient ◽  
Viscous Effects ◽  
Total Uncertainty ◽  
Pumping Station ◽  
Pumping System ◽  
Test Loop ◽  
Useful Power

The pumping station with symmetric aerofoil can achieve reversible pumping function. It can keep high reversible efficiency and its flow coefficient is approaching to normal one. At same time, it has the simple structure and is easy to operate and maintain. The flow inside reversible pumping station is very complex and dominated by three dimensional viscous effects. With the rapid progress of computational fluid dynamics, CFD has become an important tool to help to make full understanding of flow. In order to recognize the characteristic of pumping station, the control volume method is used to simulation the flow filed. The RNG k-ε turbulent model and SIMPLEC algorithm are applied to do analysis. Flow field inside symmetric aerofoil blade and passage of pumping station are analyzed in detail. Some computational data, such as computational contour of sections, streamline of pumping system, flow vectors of blade and pressure contour of blade for two different rotate directional, are given in the paper. On the based of the simulation results, efficiency prediction of the pumping station is applied. By calculating the useful power and the hydraulic efficiency at the 11 different discharge points, capabilities of pumping station are predicted. A set of model pumping station with a 300mm blade are made for test. Using the laboratory test loop of which the total uncertainty of measured efficiency is ±0.39%, the hydraulic performance is evaluated and demonstrated. The numerical performances agree well with experiment data.

scholarly journals ICCM2015: A Comparison of RANS and LES Computational Methods in Analyzing Ventilation Flow Through a Room Fitted with a Two-Sided Windcatcher

2017 ◽  
Vol 14 (03) ◽  
pp. 1750021 ◽  
Author(s):  
A. Niktash ◽  
B. P. Huynh
Keyword(s):  
Natural Ventilation ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Interior Space ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
Cfd Method ◽  
Good Agreement

A windcatcher is a structure for providing natural ventilation using wind power; it is usually fitted on the roof of a building to exhaust the inside stale air to the outside and supplies the outside fresh air into the building interior space working by pressure difference between outside and inside of the building. In this paper, the behavior of free wind flow through a three-dimensional room fitted with a centered position two-canal bottom shape windcatcher model is investigated numerically, using a commercial computational fluid dynamics (CFD) software package and LES (Large Eddy Simulation) CFD method. The results have been compared with the obtained results for the same model but using RANS (Reynolds Averaged Navier–Stokes) CFD method. The model with its surrounded space has been considered in both method. It is found that the achieved results for the model from LES method are in good agreement with RANS method’s results for the same model.

Computations of bladerow stall inception in transonic flows

1999 ◽  
Vol 103 (1025) ◽  
pp. 317-324 ◽  
Author(s):  
L. He ◽  
J. O. Ismael
Keyword(s):  
Three Dimensional ◽  
Rotating Stall ◽  
Navier Stokes ◽  
Flow Conditions ◽  
Stall Inception ◽  
Tip Leakage ◽  
Blade Row ◽  
Inflow Condition ◽  
Shock Oscillation ◽  
Transonic Fan

Abstract A three-dimensional unsteady Navier-Stokes solver has been used to simulate stall inception in a single row ten passage segment of a transonic fan, the NASA rotor-67. At subsonic flow conditions, the 3D results illustrate a rotating stall inception with short scale part-span cells rotating at around 80% rotor speed, similar to that observed in some low speed experiments. However, at a supersonic relative inflow condition, the results show that an isolated blade row tends to stall in a one-dimensional breakdown pattern without first experiencing rotating stall. At near-stall conditions, significant self-excited unsteadiness is generated by the interaction between the tip-leakage vortex and the passage shock wave. Further computations for two-dimensional configurations indicate that it is possible to have a rotating pattern of instability in transonic blade rows associated with circumferential synchronised shock oscillation.

scholarly journals The Effect of the Inlet Boundary Layer on the Tip Flow Field in a Transonic Fan Rotor

1998 ◽  
Author(s):  
Junji Takado ◽  
Toyotaka Sonoda ◽  
Satoshi Nakamura
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Interaction Region ◽  
Operating Conditions ◽  
Laser Doppler Velocimeter ◽  
Intensity Level ◽  
Pressure Surface ◽  
Transonic Fan

Experimental and numerical investigations have been carried out to understand the effects of the inlet boundary layer (IBL) on the tip flow field including the aerodynamic performance in a transonic fan rotor. Both the steady and the unsteady phenomena in the tip flow field have been investigated for operating conditions near peak efficiency and near stall with the two types of tip IBL. In order 10 study these phenomena, high response pressure data with Kulite transducers and laser doppler velocimeter (LDV) data have been acquired around the tip region. Furthermore, three-dimensional Navier-Stokes numerical simulations have been compared with the measured results. The results indicate that the tip IBL significantly influences the spanwise distribution of pressure ratio around the tip region and the stall characteristics including the passage shock / tip leakage vortex interaction, the blockage generation, the wake structure, and the unsteadiness of the tip flow field. In particular, at a near stall condition for the thick IBL with high turbulence intensity level, the tip diffusion level is increased due to a larger blockage, which is generated downstream of a much stronger interaction region. These phenomena are a consequence of the low momentum fluid in the tip IBL, and significantly reduce the stall margin. Furthermore, the unsteadiness drastically increases around the interaction region and around the pressure surface where the blockage migrates. These unsteady phenomena are distinctive features near stall. Downstream of the rotor, the larger and more unsteady blockage is discharged from the pressure surface side, and complicates the three-dimensional rotor exit flow field around the tip region.

Numerical Prediction of Permeability Tensor for Three Dimensional Circular Braided Preform by considering Intra-tow Flow

2005 ◽  
Vol 13 (4) ◽  
pp. 323-334 ◽  
Author(s):  
Y.S. Song ◽  
K. Chung ◽  
T.J. Kang ◽  
J.R. Youn
Keyword(s):  
Control Volume ◽  
Three Dimensional ◽  
Unit Cell ◽  
Permeability Tensor ◽  
Resin Flow ◽  
Resin Transfer Moulding ◽  
Moulding Process ◽  
Flow Through ◽  
Transfer Moulding ◽  
Control Volume Finite Element

Resin transfer moulding is characterized by the permeability tensor, which is a measure of the resistance to resin flow through the preform. Complete prediction of the second order permeability tensor for three dimensional circular braided preforms is critical to an understanding of the resin transfer moulding process. The permeability can be predicted by considering resin flow through the multi-axial fibre structure. In this study, the permeability tensor for a 3-D circular braided preform was calculated by solving a boundary problem of a periodic unit cell. The flow field through the unit cell was obtained by using a 3-D control volume finite element method (CVFEM) and Darcy's law was utilized to obtain the permeability tensor. The flow analyses were carried out for two cases, one in which the fibre tow was regarded as a permeable porous medium, and one in which it was regarded as an impermeable solid. It was found that the flow within the intra-tow region of the braided preform was negligible if the inter-tow porosity was relatively high, but flow through the tow, especially flow in the thickness direction must be considered when the porosity is low. The permeability of the braided preform was measured by a radial flow experiment and compared with the predicted permeability.

Sign in / Sign up

Export Citation Format

Share Document