A High-Loaded Axial Compressor Bifurcate Stator Blade Aerodynamic Design and Vorticity Dynamics Diagnosis for Flow Structure

On the flow instability caused by large scale boundary-layer flow separation in highly loaded compressor/fan blade passage, a novel bifurcate compressor blade is designed based on pressure gradient control idea for blade passage flow, and a distinctive variable solidity bifurcate blade concept and three-dimensional blade design technology are integrated to achieve this design idea in this paper. The quantitative flow information for the bifurcate blade passage is obtained by numerical simulation method to investigate the separation flow structure and dynamic mechanism near the wall and in the wake flow area. Besides, the complex influence of vortex structure evolution and the dynamic mechanism of low energy fluid redistribution being controlled in boundary-layer flow area would be revealed by applying the vorticity dynamics theory. The variable law of design parameters is explored in order to decrease aerodynamic loss, to delay flow separation near the wall and corner for the blade surface, to restructure blade aerodynamic loading, to form gentle pressure gradient and to diminish wake flow loss. The results indicate that although extra aerodynamic loss is generated by the geometric mutation of bifurcate segment, the bifurcate blade effectively restrains the migration of high-entropy secondary flow fluid in the shroud corner area, thus substantially decreasing the loss near endwall/corner, which remarkably promotes the aerodynamic performance, particularly under the condition of positive incidence angle. Moreover, the bifurcate blade skillfully remolds the pressure gradient on the blade surface, and promotes total pressure as well as velocity for the wake area that would be beneficial for the downstream rotor blade. With the introduction of key physical concepts and flow parameters of vortex/vorticity dynamics, such as boundary vorticity flux, vorticity vector, skin-friction vector and tangential pressure gradient, the physical root source and mechanism of gentle pressure gradient formation, wake flow structure being weakened, and flow separation reduction for the endwall and corner are further revealed.

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Influence of Periodically Unsteady Wake Flow on the Flow Separation in Blade Channels

Volume 1: Turbomachinery ◽

10.1115/90-gt-253 ◽

1990 ◽

Author(s):

G. H. Dibelius ◽

E. Ahlers

Keyword(s):

Boundary Layer ◽

Flat Plate ◽

Flow Separation ◽

Boundary Layer Flow ◽

Turbine Blades ◽

Suction Side ◽

Wake Flow ◽

Test Channel ◽

Theoretical Understanding ◽

Layer Flow

The influence of periodically unsteady perturbations on the turbulent flow along the suction side of turbine blades is investigated in a test rig. The blade suction side is represented by a flat plate of 550 mm length. The pressure profile typically encountered in a turbine blade channel is generated by a curved wall opposite to the flat plate. The angle of the divergent part of the test channel and hence the pressure can be increased to induce flow separation on the flat plate. For simulation of the wakes from the upstream blade row the incoming flow is periodically disturbed by a wake generator consisting of five flat profiles arranged in front and parallel to the plate rotating with adjustable speed and phase angle. A LDV with high spatial resolution is used to measure averaged and fluctuating components of the velocity inside the boundary layer flow down to a distance of y = 0,05 mm from the plate surface determining the boundary layer parameters as well as the wall shear stress. By Fourier analysis of the measured time related velocity distributions the stochastic and periodic parts of the overall turbulence are identified. With a periodic wake flow the separation is shifted downstream as compared to the steady flow situation. This is due to the energization of the boundary layer flow associated with the conversion of periodic in stochastic parts of the turbulence. Conclusions resulting from the experimental findings for the theoretical understanding of the flow in turbine cascades are discussed in particular with respect to turbulence modelling.

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Influence of Periodically Unsteady Wake Flow on the Flow Separation in Blade Channels

Journal of Turbomachinery ◽

10.1115/1.2927973 ◽

1992 ◽

Vol 114 (1) ◽

pp. 108-113 ◽

Cited By ~ 2

Author(s):

G. H. Dibelius ◽

E. Ahlers

Keyword(s):

Boundary Layer ◽

Flat Plate ◽

Flow Separation ◽

Boundary Layer Flow ◽

Turbine Blades ◽

Suction Side ◽

Wake Flow ◽

Test Channel ◽

Theoretical Understanding ◽

Layer Flow

The influence of periodically unsteady perturbations on the turbulent flow along the suction side of turbine blades is investigated in a test rig. The blade suction side is represented by a flat plate 550 mm in length. The pressure profile typically encountered in a turbine blade channel is generated by a curved wall opposite to the flat plate. The angle of the divergent part of the test channel and hence the pressure can be increased to induce flow separation on the flat plate. For simulation of the wakes from the upstream blade row, the incoming flow is periodically disturbed by a wake generator consisting of five flat profiles arranged in front and parallel to the plate rotating with adjustable speed and phase angle. An LDV with high spatial resolution is used to measure averaged and fluctuating components of the velocity inside the boundary layer flow down to a distance of y = 0.05 mm from the plate surface, determining the boundary layer parameters as well as the wall shear stress. By Fourier analysis of the measured time-related velocity distributions, the stochastic and periodic parts of the overall turbulence are identified. With a periodic wake flow the separation is shifted downstream as compared to the steady flow situation. This is due to the energization of the boundary layer flow associated with the conversion of periodic in stochastic parts of the turbulence. Conclusions resulting from the experimental findings for the theoretical understanding of the flow turbine cascades are discussed in particular with respect to turbulence modeling.

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Effects of obliqueness on mixing layer flow structure

Proceeding of THMT-15. Proceedings of the Eighth International Symposium On Turbulence Heat and Mass Transfer ◽

10.1615/ichmt.2015.thmt-15.210 ◽

2015 ◽

Author(s):

M. Karimi ◽

Sharath S. Girimaji

Keyword(s):

Flow Structure ◽

Mixing Layer ◽

Layer Flow

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

Energies ◽

10.3390/en14133745 ◽

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.

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Effects of Roughness Strip and Acoustic Sensor Height on Subsonic Boundary Layer by Experiment

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.421.459 ◽

2013 ◽

Vol 421 ◽

pp. 459-463

Author(s):

Ning Zong ◽

Guang Jun Yang ◽

Jing Sun

Keyword(s):

Boundary Layer ◽

Flow Structure ◽

Dynamic Test ◽

Acoustic Sensor ◽

Body Type ◽

Test Plate ◽

Spectrum Measurement ◽

Layer Flow ◽

Analysis System ◽

Wind Speed Measurement

According to the measurement requirements of acoustic fatigue load on aft fuselage structure and the external installation restriction of the acoustic sensor on aircraft surface, an acoustic sensor is installed on the silencing jet test plate with reference to body type of the real aircraft. A dynamic test and analysis system combined hot wire wind speed measurement and acoustic spectrum measurement is built up for the combined experiments with different acoustic sensor height and various boundary layer flow structure at subsonic flow condition. Turbulence development of different boundary layer is analyzed. The test result can be coordinated with the local measurement to aircraft flow structure so as to estimate the effect of acoustic sensor on the flow field.

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Numerical simulation of supersonic turbulent boundary layer flow with mild pressure gradient

10.2514/6.1996-2059 ◽

1996 ◽

Author(s):

E. Fick ◽

D. Gaitonde ◽

T. Buter

Keyword(s):

Numerical Simulation ◽

Boundary Layer ◽

Turbulent Boundary Layer ◽

Pressure Gradient ◽

Boundary Layer Flow ◽

Turbulent Boundary Layer Flow ◽

Layer Flow

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Manipulating flow separation: sensitivity of stagnation points, separatrix angles and recirculation area to steady actuation

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2014.0365 ◽

2014 ◽

Vol 470 (2170) ◽

pp. 20140365 ◽

Cited By ~ 5

Author(s):

E. Boujo ◽

F. Gallaire

Keyword(s):

Flow Separation ◽

Separation Point ◽

Navier Stokes ◽

Reattachment Point ◽

Amplitude Control ◽

Geometric Quantity ◽

Stagnation Points ◽

Recirculation Area ◽

Layer Flow ◽

Analytical Expressions

A variational technique is used to derive analytical expressions for the sensitivity of several geometric indicators of flow separation to steady actuation. Considering the boundary layer flow above a wall-mounted bump, the six following representative quantities are considered: the locations of the separation point and reattachment point connected by the separatrix, the separation angles at these stagnation points, the backflow area and the recirculation area. For each geometric quantity, linear sensitivity analysis allows us to identify regions which are the most sensitive to volume forcing and wall blowing/suction. Validations against full nonlinear Navier−Stokes calculations show excellent agreement for small-amplitude control for all considered indicators. With very resemblant sensitivity maps, the reattachment point, the backflow and recirculation areas are seen to be easily manipulated. By contrast, the upstream separation point and the separatrix angles are seen to remain extremely robust with respect to external steady actuation.

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Boundary Layer Flashback Model for Hydrogen Flames in Confined Geometries Including the Effect of Adverse Pressure Gradient

Volume 4A: Combustion, Fuels, and Emissions ◽

10.1115/gt2020-14164 ◽

2020 ◽

Author(s):

Ólafur H. Björnsson ◽

Sikke A. Klein ◽

Joeri Tober

Keyword(s):

Boundary Layer ◽

Pressure Gradient ◽

Flow Separation ◽

Gradient Flow ◽

Lewis Number ◽

Adverse Pressure Gradient ◽

Future Research ◽

Diffuser Flow ◽

Combustion Properties ◽

Quenching Distance

Abstract The combustion properties of hydrogen make premixed hydrogen-air flames very prone to boundary layer flashback. This paper describes the improvement and extension of a boundary layer flashback model from Hoferichter [1] for flames confined in burner ducts. The original model did not perform well at higher preheat temperatures and overpredicted the backpressure of the flame at flashback by 4–5x. By simplifying the Lewis number dependent flame speed computation and by applying a generalized version of Stratford’s flow separation criterion [2], the prediction accuracy is improved significantly. The effect of adverse pressure gradient flow on the flashback limits in 2° and 4° diffusers is also captured adequately by coupling the model to flow simulations and taking into account the increased flow separation tendency in diffuser flow. Future research will focus on further experimental validation and direct numerical simulations to gain better insight into the role of the quenching distance and turbulence statistics.

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Effects of Area Ratio and Mean Rise Angle on the Aerodynamics of Interturbine Ducts

Journal of Turbomachinery ◽

10.1115/1.4039936 ◽

2018 ◽

Vol 140 (9) ◽

Cited By ~ 1

Author(s):

Yanfeng Zhang ◽

Shuzhen Hu ◽

Ali Mahallati ◽

Xue-Feng Zhang ◽

Edward Vlasic

Keyword(s):

Boundary Layer ◽

Pressure Gradient ◽

Static Pressure ◽

Computational Study ◽

Pressure Rise ◽

Adverse Pressure Gradient ◽

Boundary Layer Separation ◽

Wake Flow ◽

Height Ratio ◽

Inlet Swirl

This work, a continuation of a series of investigations on the aerodynamics of aggressive interturbine ducts (ITD), is aimed at providing detailed understanding of the flow physics and loss mechanisms in four different ITD geometries. A systematic experimental and computational study was carried out by varying duct outlet-to-inlet area ratios (ARs) and mean rise angles while keeping the duct length-to-inlet height ratio, Reynolds number, and inlet swirl constant in all four geometries. The flow structures within the ITDs were found to be dominated by the boundary layer separation and counter-rotating vortices in both the casing and hub regions. The duct mean rise angle determined the severity of adverse pressure gradient in the casing's first bend, whereas the duct AR mainly governed the second bend's static pressure rise. The combination of upstream wake flow and the first bend's adverse pressure gradient caused the boundary layer to separate and intensify the strength of counter-rotating vortices. At high mean rise angle, the separation became stronger at the casing's first bend and moved farther upstream. At high ARs, a two-dimensional separation appeared on the casing and resulted in increased loss. Pressure loss penalties increased significantly with increasing duct mean rise angle and AR.

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