Tip Speed Ratio Influences on Rotationally Augmented Boundary Layer Topology and Aerodynamic Force Generation

2004 ◽  
Vol 126 (4) ◽  
pp. 1025-1033 ◽  
Author(s):  
S. Schreck ◽  
M. Robinson
Keyword(s):  
Flow Field ◽  
Surface Pressure ◽  
Aerodynamic Force ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Speed Ratio ◽  
Pressure Data ◽  
Tip Speed Ratio ◽  
Normal Forces

Under zero yaw conditions, rotational effects substantially and routinely augment HAWT blade aerodynamic response. To better comprehend the fluid dynamic mechanisms underlying this phenomenon, time dependent blade surface pressure data were acquired from the National Renewable Energy Laboratory (NREL) Unsteady Aerodynamics Experiment (UAE), a full-scale HAWT tested in the NASA Ames 80 ft×120 ft wind tunnel. These surface pressure data were processed to obtain normal force and flow field topology data. Further analyses were carried out in a manner that allowed tip speed ratio effects to be isolated from other confounding influences. Results showed clear correlations between normal forces, flow field topologies, and tip speed ratios. These relationships changed significantly at different blade radial locations, pointing to the complex three-dimensional flow physics present on rotating HAWT blades.

scholarly journals Coupled Fluid–Solid Numerical Simulation for Flow Field Characteristics and Supporting Performance of Flexible Support Cylindrical Gas Film Seal

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 97
Author(s):  
Junfeng Sun ◽  
Meihong Liu ◽  
Zhen Xu ◽  
Taohong Liao ◽  
Xiangping Hu ◽  
...  
Keyword(s):  
Flow Field ◽  
Film Thickness ◽  
Fluid Dynamic ◽  
Structural Characteristics ◽  
Structural Parameters ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
High Rotational Speed ◽  
Flexible Support ◽  
Flow Field Characteristics

A new type of cylindrical gas film seal (CGFS) with a flexible support is proposed according to the working characteristics of the fluid dynamic seal in high-rotational-speed fluid machinery, such as aero-engines and centrifuges. Compared with the CGFS without a flexible support, the CGFS with flexible support presents stronger radial floating characteristics since it absorbs vibration and reduces thermal deformation of the rotor system. Combined with the structural characteristics of a film seal, an analytical model of CGFS with a flexible wave foil is established. Based on the fluid-structure coupling analysis method, the three-dimensional flow field of a straight-groove CGFS model is simulated to study the effects of operating and structural parameters on the steady-state characteristics and the effects of gas film thickness, eccentricity, and the number of wave foils on the equivalent stress of the flexible support. Simulation results show that the film stiffness increases significantly when the depth of groove increases. When the gas film thickness increases, the average equivalent stress of the flexible support first decreases and then stabilizes. Furthermore, the number of wave foils affects the average foils thickness. Therefore, when selecting the number of wave foils, the support stiffness and buffer capacity should be considered simultaneously.

Time-Averaged and Time-Accurate Aerodynamic Effects of Forward Rotor Cavity Purge Flow for a High-Pressure Turbine: Part I—Analytical and Experimental Comparisons

2012 ◽  
Author(s):  
Brian R. Green ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Film Cooling ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Flow Path ◽  
Field Analysis ◽  
High Pressure Turbine ◽  
Purge Flow

The effect of rotor purge flow on the unsteady aerodynamics of a high-pressure turbine stage operating at design corrected conditions has been investigated both experimentally and computationally. The experimental configuration consisted of a single-stage high-pressure turbine with a modern film-cooling configuration on the vane airfoil as well as the inner and outer end-wall surfaces. Purge flow was introduced into the cavity located between the high-pressure vane and the high-pressure disk. The high-pressure blades and the downstream low-pressure turbine nozzle row were not cooled. All hardware featured an aerodynamic design typical of a commercial high-pressure ratio turbine, and the flow path geometry was representative of the actual engine hardware. In addition to instrumentation in the main flow path, the stationary and rotating seals of the purge flow cavity were instrumented with high frequency response, flush-mounted pressure transducers and miniature thermocouples to measure flow field parameters above and below the angel wing. Predictions of the time-dependent flow field in the turbine flow path were obtained using FINE/Turbo, a three-dimensional, Reynolds-Averaged Navier-Stokes CFD code that had the capability to perform both steady and unsteady analysis. The steady and unsteady flow fields throughout the turbine were predicted using a three blade-row computational model that incorporated the purge flow cavity between the high-pressure vane and disk. The predictions were performed in an effort to mimic the design process with no adjustment of boundary conditions to better match the experimental data. The time-accurate predictions were generated using the harmonic method. Part I of this paper concentrates on the comparison of the time-averaged and time-accurate predictions with measurements in and around the purge flow cavity. The degree of agreement between the measured and predicted parameters is described in detail, providing confidence in the predictions for flow field analysis that will be provided in Part II.

scholarly journals Numerical and Analytical Study of Fluid Dynamic Forces in Seals and Bearings

1988 ◽  
Vol 110 (3) ◽  
pp. 315-325 ◽  
Author(s):  
L. T. Tam ◽  
A. J. Przekwas ◽  
A. Muszynska ◽  
R. C. Hendricks ◽  
M. J. Braun ◽  
...  
Keyword(s):  
Flow Field ◽  
Stokes Equations ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Circumferential Velocity ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Lumped Model ◽  
Destabilizing Factors ◽  
Recirculation Zones

A numerical model based on a transformed, conservative form of the three-dimensional Navier-Stokes equations and an analytical model based on “lumped” fluid parameters are presented and compared with studies of modeled rotor/bearing/seal systems. The rotor destabilizing factors are related to the rotative character of the flow field. It is shown that these destabilizing factors can be reduced through a descrease in the fluid average circumferential velocity. However, the rotative character of the flow field is a complex three-dimensional system with bifurcated secondary flow patterns that significantly alter the fluid circumferential velocity. By transforming the Navier-Stokes equations to those for a rotating observer and using the numerical code PHOENICS-84 with a nonorthogonal body fitted grid, several numerical experiments were carried out to demonstrate the character of this complex flow field. In general, fluid injection and/or preswirl of the flow field opposing the shaft rotation significantly intensified these secondary recirculation zones and thus reduced the average circumferential velocity, while injection or preswirl in the direction of rotation significantly weakened these zones. A decrease in average circumferential velocity was related to an increase in the strength of the recirculation zones and thereby promoted stability. The influence of the axial flow was analyzed. The lumped model of fluid dynamic force based on the average circumferential velocity ratio (as opposed to the bearing/seal coefficient model) well described the obtained results for relatively large but limited ranges of parameters. This lumped model is extremely useful in rotor/bearing/seal system dynamic analysis and should be widely recommended. Fluid dynamic forces and leakage rates were calculated and compared with seal data where the working fluid was bromotrifluoromethane (CBrF3). The radial and tangential force predictions were in reasonable agreement with selected experimental data. Nonsynchronous perturbation provided meaningful information for system lumped parameter identification from numerical experiment data.

Investigation of the Flow Field on a Transonic Turbine Nozzle Guide Vane With Rim Seal Cavity Flow Ejection

2009 ◽  
Author(s):  
M. Pau ◽  
G. Paniagua
Keyword(s):  
Flow Field ◽  
Static Pressure ◽  
Numerical Study ◽  
Guide Vane ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Cavity Flow ◽  
Trailing Edge ◽  
Dynamic Simulations ◽  
Purge Flow

Ensuring an adequate life of high pressure turbines requires efficient cooling methods, such as rim seal flow ejection from the stator-rotor wheel space cavity interface, which prevents hot gas ingress into the rotor disk. The present work addresses the potential to improve the efficiency in transonic turbines at certain rim seal ejection rates. To understand this process a numerical study was carried out combining computational fluid dynamic simulations (CFD) and experiments on a single stage axial test turbine. The three dimensional steady CFD analysis was performed modeling the purge cavity flow ejected downstream of the stator blade row, at three flow regimes, subsonic M2 = 0.73, transonic M2 = 1.12 and supersonic M2 = 1.33. Experimental static pressure measurements were used to calibrate the computational model. The main flow field-purge flow interaction is found to be governed by the vane shock structures at the stator hub. The interaction between the vane shocks at the hub and the purge flow has been studied and quantitatively characterized as function of the purge ejection rate. The ejection of 1% of the core flow from the rim seal cavity leads to an increase of the hub static pressure of approximately 7% at the vane trailing edge. This local reduction of the stator exit Mach number decreases the trailing edge losses in the transonic regime. Finally, a numerically predicted loss breakdown is presented, focusing on the relative importance of the trailing edge losses, boundary layer losses, shock losses and mixing losses, as a function of the purge rate ejected. Contrary to the experience in subsonic turbines, results in a transonic model demonstrate that ejecting purge flow improves the vane efficiency due to the shock structures modification downstream of the stator.

scholarly journals An Actuator Disc Analysis of a Ducted High-Solidity Tidal Turbine in Yawed Flow

2019 ◽  
Author(s):  
Mitchell G. Borg ◽  
Qing Xiao ◽  
Atilla Incecik ◽  
Steven Allsop ◽  
Christophe Peyrard
Keyword(s):  
Fluid Dynamic ◽  
Computational Fluid Dynamic Model ◽  
Hydrodynamic Performance ◽  
Speed Ratio ◽  
Angular Range ◽  
Power Development ◽  
Tip Speed Ratio ◽  
Power Increase ◽  
Actuator Disc ◽  
Tidal Turbine

Abstract This work elaborates a computational fluid dynamic model utilised in the investigation of the hydrodynamic performance concerning a ducted high-solidity tidal turbine in yawed inlet flows. Analysing the performance at distinct bearing angles with the axis of the turbine, increases in torque and mechanical rotational power were acknowledged to be induced within a limited angular range at distinct tip-speed ratio values. Through multiple yaw iterations, the peak attainment was found to fall between bearing angles of 15° and 30°, resulting in a maximum power increase of 3.22%, together with an extension of power development to higher tip-speed ratios. In confirmation, these outcomes were subsequently analysed by means of actuator disc theory, attaining a distinguishable relationship with blade-integrated outcomes.

426 Research on the Flow Field around Low Tip Speed Ratio Type Straight Blade Vertical Axis Wind Turbine

2013 ◽  
Vol 2013.62 (0) ◽  
pp. 257-258
Author(s):  
Toshiaki KAWABATA ◽  
Takao MAEDA ◽  
Yasunari KAMADA ◽  
Junsuke MURATA ◽  
Qing'an LI
Keyword(s):  
Flow Field ◽  
Wind Turbine ◽  
Vertical Axis ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Straight Blade ◽  
Tip Speed Ratio

Structures and Interactions Underlying Rotational Augmentation of Blade Aerodynamic Response

2003 ◽  
Author(s):  
S. Schreck ◽  
M. Robinson
Keyword(s):  
Surface Pressure ◽  
Normal Force ◽  
Unsteady Aerodynamics ◽  
Boundary Layer Separation ◽  
Time Dependent ◽  
Blade Surface ◽  
Pressure Data ◽  
Pressure Distributions ◽  
Standard Deviations ◽  
Tunnel Time

Blade rotation routinely and significantly augments aerodynamic forces during zero yaw HAWT operation. To better understand the flow physics underlying this phenomenon, time dependent blade surface pressure data were acquired from the NREL Unsteady Aerodynamics Experiment, a full-scale HAWT tested in the NASA Ames 80 ft × 120 Ft wind tunnel. Time records of surface pressures and normal force were processed to obtain means and standard deviations. Surface pressure means and standard deviations were analyzed to identify boundary layer separation and reattachment locations. Separation and reattachment kinematics were then correlated with normal force behavior. Results showed that rotational augmentation was linked to specific separation and reattachment behaviors, and to associated three-dimensionality in surface pressure distributions.

Theoretical Study of the Three-Dimensional Flow Field in the Calender Bank

2003 ◽  
Author(s):  
S. Luther ◽  
D. Mewes ◽  
R. H. Schuster
Keyword(s):  
Free Surface ◽  
Flow Field ◽  
Product Quality ◽  
Three Dimensional ◽  
Flow Behaviour ◽  
Stream Line ◽  
Speed Ratio ◽  
Three Dimensional Flow ◽  
Specific Product ◽  
Dimensional Flow

The three-dimensional flow field in the calender gap is calculated with consideration of the free surface of the bank. Calender units with rotating rolls are used to produce foils or sheets from polymer material with viscous or elastometric flow properties. The flow field and the adjusting form of the bank determine the properties of the product. The results of the calculations include the determiniation of vortex patterns inside the bank for fluids with viscous non-Newtonian and Newtonian flow behaviour as well as the determination of the influence of gap height and speed ratio on the coordinates of the free surface and the flow field. Additionally the influence of the flow field on the product quality is presented. Due to the requirement of a good product quality the influencing parameters are subject to boundaries. Such boundaries of the parameters are discussed and a schematic processing window for a specific product geometry is given. Analysed product properties are thickness, surface appearance, air inclusions, mixing and temperature. The numerical calculation is based on a decoupled calculation method for the free surface. The transport equation for mass and impulse are solved with the fluid dynamics analysis package Polyflow. The coordinates of the free surface are shifted until the free surface becomes a stream line. To analyse the flow behaviour polymeric fluids the power-law model of Ostwald-de-Waele is used.

Time-Averaged and Time-Accurate Aerodynamic Effects of Forward Rotor Cavity Purge Flow for a High-Pressure Turbine—Part I: Analytical and Experimental Comparisons

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Brian R. Green ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Film Cooling ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Flow Path ◽  
Field Analysis ◽  
High Pressure Turbine ◽  
Purge Flow

The effect of rotor purge flow on the unsteady aerodynamics of a high-pressure turbine stage operating at design corrected conditions has been investigated, both experimentally and computationally. The experimental configuration consisted of a single-stage high-pressure turbine with a modern film-cooling configuration on the vane airfoil and the inner and outer end wall surfaces. Purge flow was introduced into the cavity located between the high-pressure vane and the high-pressure disk. The high-pressure blades and the downstream low-pressure turbine nozzle row were not cooled. All of the hardware featured an aerodynamic design typical of a commercial high-pressure ratio turbine and the flow path geometry was representative of the actual engine hardware. In addition to instrumentation in the main flow path, the stationary and rotating seals of the purge flow cavity were instrumented with high frequency response flush-mounted pressure transducers and miniature thermocouples in order to measure the flow field parameters above and below the angel wing. Predictions of the time-dependent flow field in the turbine flow path were obtained using FINE/Turbo, a three-dimensional Reynolds-averaged Navier–Stokes computational fluid dynamics CFD code that had the capability to perform both a steady and unsteady analysis. The steady and unsteady flow fields throughout the turbine were predicted using a three blade-row computational model that incorporated the purge flow cavity between the high-pressure vane and disk. The predictions were performed in an effort to mimic the design process with no adjustment of boundary conditions to better match the experimental data. The time-accurate predictions were generated using the harmonic method. Part I of this paper concentrates on the comparison of the time-averaged and time-accurate predictions with measurements in and around the purge flow cavity. The degree of agreement between the measured and predicted parameters is described in detail, providing confidence in the predictions for the flow field analysis that will be provided in Part II.

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