A Comparison of the Wake Effects Generated by the Biased Triangle Bar and Traditional Cylinder Bar to the Boundary Layer on Suction Surface of LPT Blade

2020 ◽  
Vol 37 (2) ◽  
pp. 153-166
Author(s):  
Sun Shuang ◽  
Li Wei ◽  
Lu Xin’gen ◽  
Zhang Yanfeng ◽  
Zhu Junqiang ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Near Field ◽  
Flow Characteristics ◽  
Wake Flow ◽  
Cylinder Wake ◽  
Suction Surface ◽  
Wake Effects ◽  
The Asymmetry ◽  
Layer Flow

AbstractConsidering the asymmetry of the low pressure turbine blade (LPT) wake at a low Reynolds number, the influence of asymmetric wakes which are similar to LPT wakes on the boundary layer of downstream blade rows in the near field is studied in the present paper, in order to increase wake flow prediction accuracy of the downstream blade without increasing the difficulty of the experiment or calculation load. Packb high-lift LPT airfoil was studied with CFX software. Following the analysis of the similarities between the wake generated by the cylinder bar and the triangle bar and the LPT blade wake in the near-field, the boundary layer flow characteristics on the suction surface under the different wakes were compared. In this research, it was found that the wakes of biased triangle bar shared more similarities with the LPT blade wake in the near field than the cylinder bar. Furthermore, the biased triangle bar wake was asymmetrical in terms of its centerline, and the separation bubble was suppressed while the calming effect was reduced after the wake-induced transition due to the asymmetry. And the time-averaged momentum thickness decreased by 7 % compared to the cylinder wake.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Reattachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Vol 126 (4) ◽  
pp. 663-676 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and reattachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Experimental Study of the Effect of Periodic Unsteady Wake Flow on Boundary Layer Development, Separation, and Re-Attachment Along the Surface of a Low Pressure Turbine Blade

2004 ◽  
Author(s):  
M. T. Schobeiri ◽  
B. O¨ztu¨rk
Keyword(s):  
Boundary Layer ◽  
Separation Bubble ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow ◽  
Layer Development

The paper experimentally studies the effects of periodic unsteady wake flow on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL), Texas A&M University. The experiments were carried out at a Reynolds number of 110,000 (based on suction surface length and exit velocity) with a free-stream turbulence intensity of 1.9%. One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies cover the entire operating range of LP turbines. In addition to the unsteady boundary layer measurements, blade surface measurements were performed at the same Reynolds number. The surface pressure measurements were also carried out at one steady and two periodic unsteady inlet flow conditions. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations and the heights defining the separation bubble were determined by carefully analyzing and examining the pressure and the mean velocity profile data. The location of boundary layer separation was independent of the reduced frequency level. However, the extent of the separation was strongly dependent on the reduced frequency level. Once the unsteady wake started to penetrate into the separation bubble, the turbulent spot produced in the wake paths caused a reduction of the separation bubble height.

Effect of Turbulence Intensity and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Re-Attachment Over the Separation Bubble Along the Suction Surface of a Low Pressure Turbine Blade

2006 ◽  
Author(s):  
B. O¨ztu¨rk ◽  
M. T. Schobeiri
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Separation Zone ◽  
Separation Bubble ◽  
Wake Flow ◽  
Combined Effects ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Unsteady Wake ◽  
Unsteady Wake Flow

The paper experimentally investigates the individual and combined effects of periodic unsteady wake flows and freestream turbulence intensity (FSTI) on flow separation along the suction surface of a low pressure turbine blade. The experiments were carried out at a Reynolds number of 110,000 based on the suction surface length and the cascade exit velocity. The experimental matrix includes freestream turbulence intensities of 1.9%, 3.0%, 8.0%, 13.0% and three different unsteady wake frequencies with the steady inlet flow as the reference configuration. Detailed boundary layer measurements are performed along the suction surface of a highly loaded turbine blade with a separation zone. Particular attention is paid to the aerodynamic behavior of the separation zone at different FSTIs at steady and periodic unsteady flow conditions. The objective of the research is (a) to quantify the effect of FSTIs on the dynamics of the separation bubble at steady inlet flow condition, and (b) to investigate the combined effects of FSTI and the unsteady wake flow on the behavior of the separation bubble. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at the Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University.

scholarly journals Effect of Reynolds Number and Periodic Unsteady Wake Flow Condition on Boundary Layer Development, Separation, and Re-Attachment Along the Suction Surface of a Low Pressure Turbine Blade

2005 ◽  
Author(s):  
B. O¨ztu¨rk ◽  
M. T. Schobeiri ◽  
David E. Ashpis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Boundary Layer Development ◽  
Unsteady Wake ◽  
Unsteady Wake Flow

The paper experimentally studies the effects of periodic unsteady wake flow and different Reynolds numbers on boundary layer development, separation and re-attachment along the suction surface of a low pressure turbine blade. The experimental investigations were performed on a large scale, subsonic unsteady turbine cascade research facility at Turbomachinery Performance and Flow Research Laboratory (TPFL) of Texas A&M University. The experiments were carried out at Reynolds numbers of 110,000 and 150,000 (based on suction surface length and exit velocity). One steady and two different unsteady inlet flow conditions with the corresponding passing frequencies, wake velocities, and turbulence intensities were investigated. The reduced frequencies chosen cover the operating range of LP turbines. In addition to the unsteady boundary layer measurements, surface pressure measurements were performed. The inception, onset, and the extent of the separation bubble information collected from the pressure measurements were compared with the hot wire measurements. The results presented in ensemble-averaged, and the contour plot forms help to understand the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number. It was found that the suction surface displayed a strong separation bubble for these three different reduced frequencies. For each condition, the locations defining the separation bubble were determined carefully analyzing and examining the pressure and mean velocity profile data. The location of the boundary layer separation was dependent of the Reynolds number. It is observed that starting point of the separation bubble and the re-attachment point move further downstream by increasing Reynolds number from 110,000 to 150,000. Also, the size of the separation bubble is smaller when compared to that for Re = 110,000.

scholarly journals Large-Eddy Simulation of Wind Turbine Flows: A New Evaluation of Actuator Disk Models

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3745
Author(s):  
Tristan Revaz ◽  
Fernando Porté-Agel
Keyword(s):  
Boundary Layer ◽  
Simple Model ◽  
Wind Turbine ◽  
Wake Flow ◽  
Test Case ◽  
Flow Solver ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Layer Flow ◽  
Advanced Model

Large-eddy simulation (LES) with actuator models has become the state-of-the-art numerical tool to study the complex interaction between the atmospheric boundary layer (ABL) and wind turbines. In this paper, a new evaluation of actuator disk models (ADMs) for LES of wind turbine flows is presented. Several details of the implementation of such models are evaluated based on a test case studied experimentally. In contrast to other test cases used in previous similar studies, the present test case consists of a wind turbine immersed in a realistic turbulent boundary-layer flow, for which accurate data for the turbine, the flow, the thrust and the power are available. It is found that the projection of the forces generated by the turbine into the flow solver grid is crucial for rotor predictions, especially for the power, and less important for the wake flow prediction. In this context, the projection of the forces into the flow solver grid should be as accurate as possible, in order to conserve the consistency between the computed axial velocity and the projected axial force. Also, the projection of the force is found to be much more important in the rotor plane directions than in the streamwise direction. It is found that for the case of a wind turbine immersed in a realistic turbulent boundary-layer flow, the potential spurious numerical oscillations originating from sharp force projections are not harmful to the results. By comparing an advanced model which computes the non-uniform distribution of the turbine forces over the rotor with a simple model which assumes uniform effects of the turbine forces, it is found that both can lead to accurate results for the far wake flow and the thrust and power predictions. However, the comparison shows that the advanced model leads to better results for the near wake flow. In addition, it is found that the simple model overestimates the rotor velocity prediction in comparison to the advanced model. These elements are explained by the lack of local feedback between the axial velocity and the axial force in the simple model. By comparing simulations with and without including the effects of the nacelle and tower, it is found that the consideration of the nacelle and tower is relatively important both for the near wake and the power prediction, due to the shadow effects. The grid resolution is not found to be critical once a reasonable resolution is used, i.e. in the order of 10 grid points along each direction across the rotor. The comparison with the experimental data shows that an accurate prediction of the flow, thrust, and power is possible with a very reasonable computational cost. Overall, the results give important guidelines for the implementation of ADMs for LES.

Large Eddy Simulation of Transitional Flow in a Compressor Cascade

2017 ◽  
Author(s):  
Syed Anjum Haider Rizvi ◽  
Joseph Mathew
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Separation Bubble ◽  
Transitional Flow ◽  
Transitional Region ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Large Eddy

At off-design conditions, when the blade Reynolds number is low, a significant part of the blade boundary layer can be transitional. Then, standard RANS models are unable to predict the flows correctly but explicit transition modeling provides some improvement. Since large eddy simulations (LES) are improvements on RANS, the performance of LES was examined by simulating a flow through a linear, compressor cascade for which experimental data are available — specifically at the Reynolds number of 210,000 based on blade chord when transition processes occur over a significant extent of the suction surface. The LES were performed with an explicit filtering approach, applying a low-pass filter to achieve sub-grid-scale modeling. Explicit 8th-order difference formulas were used to obtain high resolution spatial derivative terms. An O-grid was wrapped around the blade with suitable clustering for the boundary layer and regions of large changes along the blade. Turbulent in-flow was provided from a precursor simulation of homogeneous, isotropic turbulence. Two LES and a DNS were performed. The second LES refines the grid in the vicinity of the separation bubble on the suction surface, and along the span. Surface pressure distributions from all simulations agree closely with experiment, thus providing a much better prediction than even transition-sensitive RANS computations. Wall normal profiles of axial velocity and fluctuations also agree closely with experiment. Differences between LES and DNS are small, but the refined grid LES is closer to the DNS almost everywhere. This monotonic convergence, expected of the LES method used, demonstrates its reliability. The pressure surface undergoes transition almost immediately downstream of the leading edge. On the suction surface there are streaks as expected for freestream-turbulence-induced transition, but spots do not appear. Instead, a separating shear layer rolls up and breaks down to turbulence at re-attachment. Both LES capture this process. Skin friction distribution reveals the transition near the re-attachment to occur over an extended region, and subsequent relaxation is slower in the LES. The narrower transition zone in the DNS is indicative of the essential role of smaller scales during transition that should not be neglected in LES. Simulation data also reveal that an assumption of laminar kinetic energy transition models that Reynolds shear stress remains small in the pre-transitional region is supported. The remaining differences in the predictions of such models is thus likely to be the separation-induced transition which preempts the spot formation.

scholarly journals Homotopy pertubation method analysis to MHD flow of a radiative nanofluid with viscous dissipation and ohmic heating over a stretching porous plate

2018 ◽  
Vol 22 (1 Part B) ◽  
pp. 413-422 ◽  
Author(s):  
Hitesh Kumar
Keyword(s):  
Boundary Layer ◽  
Viscous Dissipation ◽  
Reverse Flow ◽  
Ohmic Heating ◽  
Complete Solution ◽  
Porous Plate ◽  
Flow Characteristics ◽  
Mhd Flow ◽  
Future Research ◽  
Layer Flow

An analytical study is performed to explore the flow and heat transfer characteristics of nanofluid (Al2O3-water and TiO3-water) over a linearly stretching porous sheet in the presence of radiation, ohmic heating, and viscous dissipation. Homotopy perturbed method is used and complete solution is presented, the results for the nanofluids velocity and temperature are obtained. The effects of various thermophysical parameters on the boundary-layer flow characteristics are displayed graphically and discussed quantitatively. The effect of viscous dissipation on the thermal boundary-layer is seen to be reverse after a fixed distance from the wall, which is very strange in nature and is the result of a reverse flow. The finding of this paper is unique and may be useful for future research on nanofluid.

Optimal growth, model reduction and control in a separated boundary-layer flow using global eigenmodes

2007 ◽  
Vol 579 ◽  
pp. 305-314 ◽  
Author(s):  
ESPEN ÅKERVIK ◽  
JÉRÔME HŒPFFNER ◽  
UWE EHRENSTEIN ◽  
DAN S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Separation Bubble ◽  
Flow Simulation ◽  
Optimal Growth ◽  
Reduced Model ◽  
Linear Quadratic ◽  
Reduced Basis ◽  
Worst Case ◽  
Layer Flow

Two-dimensional global eigenmodes are used as a projection basis both for analysing the dynamics and building a reduced model for control in a prototype separated boundary-layer flow. In the present configuration, a high-aspect-ratio smooth cavity-like geometry confines the separation bubble. Optimal growth analysis using the reduced basis shows that the sum of the highly non-normal global eigenmodes is able to describe a localized disturbance. Subject to this worst-case initial condition, a large transient growth associated with the development of a wavepacket along the shear layer followed by a global cycle related to the two unstable global eigenmodes is found. The flow simulation procedure is coupled to a measurement feedback controller, which senses the wall shear stress at the downstream lip of the cavity and actuates at the upstream lip. A reduced model for the control optimization is obtained by a projection on the least stable global eigenmodes, and the resulting linear-quadratic-Gaussian controller is applied to the Navier–Stokes time integration. It is shown that the controller is able to damp out the global oscillations.

Aerodynamic Investigation of a Passive Secondary Jet Exciting a Separation Bubble for a Blunt Flat Plate

2015 ◽  
Author(s):  
Christian Helcig ◽  
Stefan aus der Wiesche ◽  
Stephan Uhkoetter
Keyword(s):  
Boundary Layer ◽  
Laser Doppler Anemometry ◽  
Separation Bubble ◽  
Flow Characteristics ◽  
Numerical Procedure ◽  
Large Eddy Simulations ◽  
Reattachment Length ◽  
Large Eddy ◽  
Low Speed Wind Tunnel ◽  
Aerodynamic Investigation

The aim of this study is to examine the influence of passive jets interacting with the separation region of the flow around a blunt plate. Experimental and numerical analysis are used to measure the velocity within the separation and reattachment region of the blunt plate with different passive jet configurations. A blunt plate was placed in a low speed wind tunnel to conduct Laser-Doppler anemometry (LDA) measurements at Re = 2.06 × 104. For the numerical procedure a dynamical sub-grid model for Large Eddy Simulations (LES) was used. For all configurations the flow characteristics such as the reattachment length were determined to characterize the boundary layer. The passive jets showed a strong influence by interacting with the boundary layer of the blunt plate.

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