A CFD-Based Prediction Method for Tip Clearance Losses and Deviations in Axial Turbines

2020 ◽  
Author(s):  
Clemens Buske
Keyword(s):  
Tip Clearance ◽  
Wake Flow ◽  
Parameter Study ◽  
Cfd Simulations ◽  
Method Performance ◽  
Local Conditions ◽  
New Model ◽  
Operation Conditions ◽  
Performance Predictions ◽  
Clearance Model

Abstract Accurate loss models are crucial for reliable turbine performance predictions using low-fidelity tools. However, the complex flow structure of the blade tip gap flow impedes an experimental deduction of a realistic tip clearance loss model. In this work, validated, high-fidelity CFD simulations are used to substitute the cost- and time-consuming experiments of a parameter study and to develop a modern, flexible and universal tip clearance model. The CFD model is based on a single stage high-pressure turbine. Inflow conditions and geometry of the rotor were specifically varied to separately study the effects of the significant parameters on the tip clearance loss and deviation. Partial correlations were formulated for each effect and combined to a new tip clearance model. Apart from commonly considered parameters such as gap height, blade loading and solidity, other parameters that are well known to have an effect but are still disregarded in most conventional loss correlations are also investigated, such as incidence, Reynolds number, rotor speed and boundary layer thickness. Furthermore, a downstream progression model is presented that reflects the local conditions of the incompletely mixed out wake flow. Interrelations between the effects are modeled by a Kriging surrogate model, which was refined by the space filling technique. The new model was validated by additional CFD simulations at unprobed operation conditions. In addition, the new model was implemented into a through flow method. Performance calculations were performed for a four-stage air turbine and compared with experimental data. In comparison with the conventional tip clearance correlations, the new model improves the performance predictions at all operation points.

The Role of Tip Clearance in High-Speed Fan Stall

1991 ◽  
Author(s):  
J. J. Adamczyk ◽  
M. L. Celestina ◽  
E. M. Greitzer
Keyword(s):  
Numerical Experiment ◽  
High Speed ◽  
Tip Clearance ◽  
Simulation Code ◽  
Tip Leakage ◽  
Flow Processes ◽  
Area Increase ◽  
Fan Blade ◽  
Clearance Model

A numerical experiment has been carried out to define the near stall casing endwall flow field of a high-speed fan rotor. The experiment used a simulation code incorporating a simple clearance model, whose calibration is presented. The results of the simulation show that the interaction of the tip leakage vortex and the in-passage shock plays a major role in determining the fan flow range. More specifically, the computations imply that it is the area increase of this vortex as it passes through the in-passage shock, which is the source of the blockage associated with stall. In addition, for fans of this type, it is the clearance over the forward portion of the fan blade which controls the flow processes leading to stall.

Numerical Investigations of Centrifugal Compressor Flows With Tip Leakage Using a Pressure Correction Method

1993 ◽  
Author(s):  
A. Tourlidakis ◽  
R. L. Elder
Keyword(s):  
Flow Pattern ◽  
High Speed ◽  
Stokes Equations ◽  
Correction Method ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Physical Models ◽  
Wake Flow ◽  
Operating Characteristics ◽  
Pressure Correction

In this paper, a three-dimensional computational model for the solution of the time-averaged Navier-Stokes equations, based on a pressure correction method and the k-ε turbulence model, is presented and implemented for the viscous flow modelling through a series of centrifugal compressors. Theoretical calculations with the current fully elliptic method are carried out and the results are compared critically with available experimental data and with results from other computational models. A radial and two backswept high-speed subsonic compressors with different geometrical and operating characteristics are analysed at design and off-design conditions. In all cases, a wake flow pattern is evident and strong secondary flows are discerned. The tip clearance effects on the relative flow pattern are found to be important and are appropriately simulated. The predictive capability of the current flow model is judged to be encouraging taking into consideration the limitations of the physical models and the numerical schemes involved in the computations.

CFD Simulation and Wind Tunnel Investigation of a FPSO Offshore Helideck Turbulent Flow

2010 ◽  
Author(s):  
Daniel Fonseca de Carvalho e Silva ◽  
Paulo Roberto Pagot ◽  
Gilder Nader ◽  
Paulo Jose´ Saiz Jabardo
Keyword(s):  
Wind Tunnel ◽  
Particle Image ◽  
Cfd Simulation ◽  
Wind Flow ◽  
Cfd Simulations ◽  
Local Conditions ◽  
British Standard ◽  
Ansys Cfx ◽  
Tunnel Model ◽  
Image Velocimetry

The offshore helideck wind flow is usually subject to many interferences. The helideck airspace velocity and turbulence fields are important issues to promote safe helicopter take-off and landing operations. The current work brings some CFD results of a helideck wind flow 3D-field defined by the local conditions and constrained by the FPSO structure. A discussion about the chosen CFD boundary conditions is also presented. These CFD results are compared with the wind tunnel model-scale velocity and turbulence measurements. The wind tunnel measurements were performed with use of two different techniques: Particle Image Velocimetry (PIV) and Constant Temperature Anemometry (CTA). The British standard CAP437: Offshore Helideck Design Criteria is examined and suggestions are made herein. The CFD simulations were conducted using the ANSYS CFX software.

Measurement and CFD Prediction of the Flow Within an HP Compressor Drive Cone

2003 ◽  
Vol 125 (1) ◽  
pp. 165-172 ◽  
Author(s):  
Christopher A. Long ◽  
Alan B. Turner ◽  
Guven Kais ◽  
Kok M. Tham ◽  
John A. Verdicchio
Keyword(s):  
Turbine Blades ◽  
Tangential Velocity ◽  
Tip Clearance ◽  
Combustion Chambers ◽  
Cfd Simulations ◽  
Blade Tip ◽  
Supporting Material ◽  
D Model ◽  
Good Agreement ◽  
Blade Tip Clearance

In some gas turbine aeroengines, the HP compressor is driven by the H.P. turbine through a conical shaft or drive cone. This drive cone is enclosed by a stationary surface that forms the supporting material for the combustion chambers. Air used to cool the turbine blades is directed into the space around the drive cone, and a major concern to an engine designer is the temperature rise in this air due to frictional dissipation and heat transfer. This paper presents results from a combined experimental and CFD investigation into the flow within an engine representative HP compressor drive cone cavity. The experimental results show similarities in flow structure to that found in classic rotor-stator systems. Both 2-D and 3-D CFD simulations were carried out using the FLUENT/UNS code. The 3-D model which included the actual compressor blade tip clearance gave the best agreement with the experimental data. However, the computational resource required to run the 3-D model limits its practical use. The 2-D CFD model, however, was found to give good agreement with experiment, providing care was exercised in selecting an appropriate value of initial tangential velocity.

Optimisation of a High Pressure Ratio Radial-Inflow Turbine: Coupled CFD-FE Analysis

2015 ◽  
Author(s):  
Mohsen Modir Shanechi ◽  
Mostafa Odabaee ◽  
Kamel Hooman
Keyword(s):  
Power Efficiency ◽  
Stokes Equations ◽  
Pressure Ratio ◽  
Tip Clearance ◽  
Von Mises Stress ◽  
Fe Method ◽  
Cfd Simulations ◽  
Turbine Wheel ◽  
Blade Thickness ◽  
Radial Inflow Turbine

The optimisation of a 5.7 air pressure ratio single stage radial-inflow turbine applied in the Sundstrand Power Systems T-100 Multipurpose Small Power Unit (MPSPU) is performed using coupled CFD-FE method. The commercial software ANSYS-Vista RTD along with a built-in module, BladeGen, is used to conduct a meanline design and, consequently, create the 3D geometry of the flow passage. Carefully examining the proposed design against the geometrical and experimental data, ANSYS-TurboGrid is applied to generate computational mesh. CFD simulations are then performed with ANSYS-CFX in which three-dimensional Reynolds-Averaged Navier-Stokes equations are solved subject to appropriate boundary conditions. Conducting the CFD simulations, the pressure and temperature distributions are imported to the ANSYS-FE module. The von Mises stress σv distribution is then calculated taking into account the centrifugal force acting on the turbine wheel. To obtain the optimised geometry, 25 major design points are regenerated where the meridional parameters, tip clearance, and blade thickness distribution are systematically changed. Furthermore, constraints are defined as high aerothermodynamic performance and acceptable vibration with a stress distribution less than yield limit of the turbine material. Results of coupled CFD-FE method show the power, efficiency, stress and deformation. Finally, performance of the optimised radial-inflow turbine indicates enhanced aero-thermodynamics (ηTS and) and structural performance (σv) compared to the MPSPU turbine design.

A Numerical Study on the Structure of Tip Clearance Flow in a Highly Forward-Swept Axial-Flow Fan

2002 ◽  
Author(s):  
Gong Hee Lee ◽  
Je Hyun Baek
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Axial Flow ◽  
Streamwise Velocity ◽  
Tip Clearance ◽  
Wake Flow ◽  
Axial Flow Fan ◽  
Step Method ◽  
Fractional Step Method ◽  
Tip Clearance Flow

A three-dimensional Navier-Stokes analysis was performed to investigate the tip clearance flows in a highly forward-swept axial flow fan operating at design condition. The numerical solution was based on a fractional step method, and two-layer k-ε model was used to obtain the eddy viscosity. The tip leakage vortex decayed very quickly inside the blade passage and, thus, no distinct leakage vortex appeared behind trailing edge. The main reason was the severe decrease of the streamwise velocity of the vortex. Also the interaction of the vortex with the casing boundary layer and the through-flow were other possibilities of the fast decay of the vortex. Comparison between the numerical results and LDV measurements data indicated that the complex viscous flow patterns inside the tip region as well as the wake flow could be properly predicted, but more refinement in numerical aspects are needed.

Numerical Study on the Influence of Tip Clearance on Rotating Stall in an Unshrouded Centrifugal Compressor

2017 ◽  
Author(s):  
Wenying Ju ◽  
Shengli Xu ◽  
Xiaofang Wang ◽  
Xudong Chen ◽  
Shuhua Yang ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Numerical Study ◽  
Leading Edge ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Forming Process ◽  
Impeller Blade ◽  
Tip Clearance Flow ◽  
Rotating Speed ◽  
Operation Conditions

Whole annulus unsteady simulations are performed by CFD with the whole flow passage model from inlet guide vanes to volute of an unshrouded centrifugal compressor. Characteristics and development mechanism of rotating stall are analyzed including the flow field and the impeller blade load in time and frequency domain. Rotating stall with three cells is observed in both two actual operation conditions but the cell rotating speed and the forming process is different. Leading edge tip clearance leakage is a criterion to predict the formation of a spike stall in centrifugal compressors. Tip clearance flow also plays an important role in the moving of rotating instabilities and the propagation of stall cells. It can effectively slow down the stall forming and decrease the pressure load on blade by reduced the tip clearance size at the leading edge.

scholarly journals Modeling and Parameter Study of Bistable Spherical Compliant Mechanisms

2011 ◽  
Author(s):  
Chester L. Smith ◽  
Craig P. Lusk
Keyword(s):  
Compliant Mechanisms ◽  
Current Model ◽  
Plane Motion ◽  
Parameter Study ◽  
Beam Model ◽  
New Model ◽  
Novel Device ◽  
Rigid Body Model ◽  
Compliant Joint ◽  
Motion Characteristics

The Bistable Spherical Compliant Mechanisms (BSCM) is a novel device capable of large, repeatable, out-of-plane motion, characteristics that are somewhat difficult to achieve with surface micro-machined MEMS. An improved pseudo-rigid-body model to predict the behavior of the BSCM is presented. The new model was used to analyze seven different versions of the device, each with a different compliant joint length. The new model, which adds torsion, is compared with a Finite-Element beam model. The new model more closely approximates the results yielded by FEA than previous models used to analyze the BSCM. Future work is needed to quantify stress-stiffening interactions between bending and torsion. Both FEA and the current model show that increasing the length of the compliant segment decreases the amount of force required to actuate the device.

Modeling of Dynamic Fluid Forces in Fast Switching Valves

2015 ◽  
Author(s):  
Daniel B. Roemer ◽  
Per Johansen ◽  
Henrik C. Pedersen ◽  
Torben O. Andersen
Keyword(s):  
Dynamic Models ◽  
Added Mass ◽  
Force Model ◽  
Cfd Simulations ◽  
Viscous Term ◽  
Fluid Force ◽  
Fluid Forces ◽  
Fast Switching ◽  
Operation Conditions ◽  
Proposed Model

Switching valves experience opposing fluid forces due to movement of the moving member itself, as the surrounding fluid volume must move to accommodate the movement. This movement-induced fluid force may be divided into three main components; the added mass term, the viscous term and the so-called history term. For general valve geometries there are no simple solution to either of these terms. During development and design of such switching valves, it is therefore, common practice to use simple models to describe the opposing fluid forces, neglecting all but the viscous term which is determined based on shearing areas and venting channels. For fast acting valves the opposing fluid force may retard the valve performance significantly, if appropriate measures are not taken during the valve design. Unsteady Computational Fluid Dynamics (CFD) simulations are available to simulate the total fluid force, but these models are computationally expensive and are not suitable for evaluating large numbers of different operation conditions or even design optimization. In the present paper, an effort is done to describe these fluid forces and their origin. An example of the total opposing fluid force is given using an analytically solvable example, showing the explicit form of the force terms and highlighting the significance of the added mass and history term in certain fast switching valve applications. A general approximate model for arbitrary valve geometries is then proposed with offset in the analytic model terms. The coefficients in this general model are determined based on CFD analyses, which are evaluated throughout the movement range of the moving member on an example valve geometry. The proposed model is compared to complete unsteady CFD simulations and found to generally predict the opposing fluid force well and gives accurate predictions under certain conditions. The proposed model is suitable for valve designers who need a computationally inexpensive fluid force model suitable for optimization routines or efficient dynamic models.

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