scholarly journals Aerodynamic Response of Turbomachinery Blade Rows to Convecting Density Wakes

2002 ◽  
Vol 124 (2) ◽  
pp. 269-274 ◽  
Author(s):  
H. S. Wijesinghe ◽  
C. S. Tan ◽  
E. E. Covert
Keyword(s):  
Shock Wave ◽  
Computational Study ◽  
Separation Bubble ◽  
Compressor Blade ◽  
Density Parameter ◽  
Two Dimensional ◽  
Suction Surface ◽  
Blade Passage ◽  
Flow Simulations ◽  
Blade Row

A two-dimensional computational study was conducted to characterize the density wake induced force and moment fluctuations on a compressor blade row. The flow simulations indicate unsteady blade excitation generated by: (1) density wake fluid directed to the blade suction surface, (2) axial deflection of the blade passage shock wave position and (3) formation of a separation bubble on the blade suction surface. The blade force and moment fluctuation amplitudes are found to scale with the nondimensional density wake width w/c and a nondimensional density parameter ρ*.

scholarly journals Aerodynamic Response of Turbomachinery Blade Rows to Convecting Density Wakes

2000 ◽  
Author(s):  
H. S. Wijesinghe ◽  
C. S. Tan ◽  
E. E. Covert
Keyword(s):  
Shock Wave ◽  
Computational Study ◽  
Separation Bubble ◽  
Compressor Blade ◽  
Density Parameter ◽  
Two Dimensional ◽  
Suction Surface ◽  
Blade Passage ◽  
Flow Simulations ◽  
Blade Row

A two–dimensional computational study was conducted to characterize the density wake induced force and moment fluctuations on a compressor blade row. The flow simulations indicate unsteady blade excitation generated by: (1) density wake fluid directed to the blade suction surface, (2) axial deflection of the blade passage shock wave position and (3) formation of a separation bubble on the blade suction surface. The blade force and moment fluctuation amplitudes are found to scale with the nondimensional density wake width w/c and a non–dimensional density parameter ρ*.

Unsteady Flow in Oscillating Turbine Cascade: Part 1 — Linear Cascade Experiment

1996 ◽  
Author(s):  
L. He
Keyword(s):  
Computational Study ◽  
Separation Bubble ◽  
Turbine Blades ◽  
Leading Edge ◽  
Computational Method ◽  
Reattachment Point ◽  
Suction Surface ◽  
Linear Cascade ◽  
Unsteady Pressure ◽  
Pressure Surface

An experimental and computational study has been carried out on a linear cascade of low pressure turbine blades with the middle blade oscillating in a torsion mode. The main objectives of the present work were to enhance understanding of the behaviour of bubble type of flow separation and to examine the predictive ability of a computational method. In addition, an attempt was made to address a general modelling issue: was the linear assumption adequately valid for such kind of flow? In Part 1 of this paper, the experimental work was described. Unsteady pressure was measured along blade surfaces using off-board mounted pressure transducers at realistic reduced frequency conditions. A short separation bubble on the suction surface near the trailing edge and a long leading-edge separation bubble on the pressure surface were identified. It was found that in the regions of separation bubbles, unsteady pressure was largely influenced by the movement of reattachment point, featured by an abrupt phase shift and an amplitude trough in the 1st harmonic distribution. The short bubble on the suction surface seemed to follow closely a laminar bubble transition model in a quasi-steady manner, and had a localized effect. The leading-edge long bubble on the pressure surface, on the other hand, was featured by a large movement of the reattachment point, which affected the surface unsteady pressure distribution substantially. As far as the aerodynamic damping was concerned, there was a destabilizing effect in the separated flow region, which was however largely balanced by the stabilizing effect downstream of the reattachment point due to the abrupt phase change.

The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 4 — Flow Fields for Incidence Angles of −1.5 and −8.5 Degrees

1989 ◽  
Author(s):  
W. C. Zierke ◽  
S. Deutsch
Keyword(s):  
Boundary Layers ◽  
Separation Bubble ◽  
Measurement Techniques ◽  
Leading Edge ◽  
Compressor Blade ◽  
Laser Doppler ◽  
Laser Doppler Velocimeter ◽  
Suction Surface ◽  
Laminar Separation ◽  
Pressure Surface

Measurements, made with laser Doppler velocimetry, about a double-circular-arc compressor blade in cascade are presented for −1.5 and −8.5 degree incidence angles and a chord Reynolds number near 500,000. Comparisons between the results of the current study and those of our earlier work at a 5.0 degree incidence are made. It is found that in spite of the relative sophistication of the measurement techniques, transition on the pressure surface at the −1.5 degree incidence is dominated by a separation “bubble” too small to be detected by the laser Doppler velocimeter. The development of the boundary layers at −1.5 and 5.0 degrees are found to be similar. In contrast to the flow at these two incidence angles, the leading edge separation “bubble” is on the pressure surface for the −8.5 degree incidence. Here, all of the measured boundary layers on the pressure surface are turbulent — but extremely thin — while on the suction surface, a laminar separation/turbulent reattachment “bubble” lies between roughly 35% and 60% chord. This “bubble” is quite thin, and some problems in interpreting backflow data.

Studies on Two-Dimensional Contouring of High-Lift Turbine Airfoil Suction Surface as Separation-Control Device: Separation Suppression Under Steady-State Flow Conditions

2011 ◽  
Author(s):  
Ken-ichi Funazaki ◽  
Nozomi Tanaka ◽  
Takahiro Shiba ◽  
Haruyuki Tanimitsu ◽  
Masaaki Hamabe
Keyword(s):  
Steady State ◽  
Separation Bubble ◽  
Control Device ◽  
Surface Boundary ◽  
Two Dimensional ◽  
Flow Conditions ◽  
Steady State Flow ◽  
Suction Surface ◽  
Airfoil Surface ◽  
State Flow

The study the present authors have been working on is to develop a new method to increase aerodynamic loading of low-pressure turbine airfoils for modern aeroengines to a great extent, which is to achieve drastic reduction of their airfoil counts. For this purpose, this study proposes two-dimensional contouring of the airfoil suction surface as a device to suppress the separation bubble that causes large aerodynamic loss, especially at low Reynolds number condition. The main objective of this paper is to show how and to what extent the surface contouring without any other disturbances affects the suction surface boundary layer accompanying separation bubble. For comparison, rather conventional tripping wire technique is also employed as “local 2D surface contouring” to generate flow disturbances in order to suppress the separation bubble. All measurements are carried out under steady-state flow conditions with low freestream turbulence. It turns out from the detailed experiments and LES analysis that the newly proposed two-dimensional contouring of the airfoil surface can effectively suppress the separation bubble, resulting in significant improvement of cascade aerodynamic performance.

CFD Simulations of Unsteady Wakes on a Highly Loaded Low Pressure Turbine Airfoil (L1A)

2012 ◽  
Author(s):  
Mounir B. Ibrahim ◽  
Samuel Vinci ◽  
Olga Kartuzova ◽  
Ralph J. Volino
Keyword(s):  
Computational Study ◽  
Separation Bubble ◽  
Low Pressure ◽  
Flow Coefficient ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Cfd Simulations ◽  
Ansys Fluent ◽  
Low Pressure Turbine ◽  
Wake Passing

A study of a very high lift, low-pressure turbine airfoil in the presence of unsteady wakes was performed computationally and compared against experimental results. The experiments were conducted in a low speed wind tunnel under high (4.9%) and then low (0.6%) freestream turbulence intensity conditions with a flow coefficient (ζ) of 0.7. The experiments were done on a linear cascade with wakes that were produced from moving rods upstream of the cascade with the rod to blade spacing varied from 1 to 1.6 to 2. In the present study two different Reynolds numbers (25,000 and 50,000, based on the suction surface length and the nominal exit velocity from the cascade) were considered. The experimental and computational data have shown that in cases without wakes, the boundary layer separated and did not reattach. The CFD was performed with Large Eddy Simulation (LES) and Unsteady Reynolds-Averaged Navier-Stokes (URANS), Transition-SST, utilizing the finite-volume code ANSYS FLUENT under the same freestream turbulence and Reynolds number conditions as the experiment but only at a rod to blade spacing of 1. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. Similar effect was predicted by 3D CFD simulations. Computational results for the pressure coefficients and velocity profiles were in a reasonable agreement with experimental ones for all cases examined. The 2D CFD efforts failed to capture the three dimensionality effects of the wake and thus were less consistent with the experimental data. As a further computational study, cases were run to simulate higher wake passing frequencies which were not run experimentally. The results of these computational cases showed that an initial 25% increase from the experimental dimensionless wake passing frequency of F = 0.45 greatly reduced the size of the separation bubble, nearly completely suppressing it, however an additional 33% increase on top of this did not prove to have much of an effect.

Vortex Structures for Highly-Loaded Subsonic Compressor Cascades With Slot Injection

2017 ◽  
Author(s):  
Huanlong Chen ◽  
Huaping Liu ◽  
Dongfei Zhang ◽  
Linxi Li
Keyword(s):  
Suction Side ◽  
Compressor Blade ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Blade Passage ◽  
Vortex Control ◽  
Analysis Theory ◽  
Numerical Simulation Methods ◽  
Linear Compressor Cascade ◽  
Highly Loaded

A promising flow analytical way to offset the respective shortcomings for the experimental measure and numerical simulation methods is presented. First, general topological rules which are applicable to the skin-friction vector lines on the passage surface, to the flow patterns in the cross-section of the cascade as well as on the blade-to-blade surface were deduced for the turbomachinery cascades with/without suction/blowing slots in this paper. Second, the qualitative analysis theory of the differential equation was used to investigate the distribution feature of the flow singular points for the limiting streamlines equation. The topological structure of the flow pattern on the cascade passage surfaces was discussed in detail. Third, the experiment and numerical simulations results for a linear compressor cascade passage with highly-loaded compound-lean slotted blade, which were combined to topologically examine the flow structure with penetrating slot injections through the blade pressure side and suction side. The results showed that the general topological rules are applicable and effective for flow diagnosis in highly-loaded compressor blade passage with slots. Finally, an integrated vortex control model, in which the blade compound-lean effect and the injection flow through the slots were coupled, was presented. The model shows that reasonable slot injection configurations can effectively control the concentrated shedding vortices from the suction surface of a highly-loaded compressor cascades passage, thereby the aerodynamic performance for the blade passage is remarkably improved. The present work provides a novel theoretical analysis method and insights of the flow for the turbine blade passage with cooling structures, aspirated compressor blade passage and other applications with new flow control configurations in turbomachinery field.

Effect of Purge on the Secondary Flow-Field of a Gas Turbine Blade-Row

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
B. D. J Schreiner ◽  
M. Wilson ◽  
Y. S. Li ◽  
C. M. Sangan
Keyword(s):  
Computational Study ◽  
Suction Side ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Pressure Side ◽  
Suction Surface ◽  
Blade Row ◽  
Purge Flow ◽  
Rotational Direction ◽  
Secondary Flow Field

Abstract Turbine disc cooling is required to protect vulnerable components from exposure to the high temperatures found in the mainstream gas path. Purge air, bled from the latter stages of the compressor, is introduced to the turbine wheelspace at low radius before exiting through the rim-seal at the periphery of the discs. The unsteady, complex flowfield that arises from the interaction between the purge and mainstream gases modifies the structure of secondary flows within the blade passage. A computational study was conducted using an unsteady Reynolds-averaged Navir–Stokes (RANS) solver, modeling an engine-representative turbine stage. Preliminary results were validated using experimental data from a test rig. The baseline secondary flowfield was described, in the absence of purge flow, demonstrating the classical rollup of the horseshoe vortex and subsequent convection of the two legs downstream. The unsteady behavior of the model was investigated and addressed, resulting in recommendations for modeling interaction phenomena in turbines. A superposed purge flow, resulting in egress through the upstream rim-seal, was shown to modify the secondary flowfield in the turbine annulus. The most notable effect of egress was the formation of a large plume forming near the pressure minima associated with the blade suction surface. The egress was turned by the mainstream flow, creating a vortical structure consistent in rotational direction to the pressure-side leg of the horseshoe vortex; the pressure-side leg was subsequently strengthened and showed an increased radial migration relative to the unpurged case. The egress plume was also shown to overwhelm the suction-side leg of the horseshoe vortex, reducing its strength.

The Measurement of Boundary Layers on a Compressor Blade in Cascade: Part 1—A Unique Experimental Facility

1987 ◽  
Vol 109 (4) ◽  
pp. 520-526 ◽  
Author(s):  
S. Deutsch ◽  
W. C. Zierke
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Pressure Distribution ◽  
Static Pressure ◽  
Compressor Blade ◽  
Boundary Layer Transition ◽  
Two Dimensional ◽  
Suction Surface ◽  
Pressure Surface ◽  
Static Pressure Distribution

A unique cascade facility is described which permits the use of laser-Doppler velocimetry (LDV) to measure blade boundary layer profiles. Because of the need for a laser access window, the facility cannot reply on continuous blade pack suction to achieve two-dimensional, periodic flow. Instead, a strong suction upstream of the blade pack is used in combination with tailboards to control the flow field. The distribution of the upstream suction is controlled through a complex baffling system. A periodic, two–dimensional flow field is achieved at a chord Reynolds number of 500,000 and an incidence angle of 5 deg on a highly loaded, double circular arc, compressor blade. Inlet and outlet flow profiles, taken using five-hole probes, and the blade static-pressure distribution are used to document the flow field for use with the LDV measurements (see Parts 2 and 3). Inlet turbulence intensity is measured, using a hot wire, to be 0.18 percent. The static-pressure distribution suggests both separated flow near the trailing edge of the suction surface and an initially laminar boundary layer profile near the leading edge of the pressure surface. Probe measurements are supplemented by sublimation surface visualization studies. The sublimation studies place boundary layer transition at 64.2 ± 3.9 percent chord on the pressure surface, and indicate separation on the suction surface at 65.6 percent ± 3.5 percent chord.

Unsteady Flow in Oscillating Turbine Cascade: Part 2 — Computational Study

1996 ◽  
Author(s):  
L. He
Keyword(s):  
Unsteady Flow ◽  
Flow Separation ◽  
Computational Study ◽  
Separation Bubble ◽  
Computational Method ◽  
Influence Coefficient ◽  
Turbine Cascade ◽  
Suction Surface ◽  
Influence Coefficient Method ◽  
Coefficient Method

Unsteady flow around a linear oscillating turbine cascade has been experimentally and computationally studied, aimed at understanding the bubble type of flow separation and examining the predictive ability of a computational method. It was also intended to check the validity of the linear assumption under an unsteady viscous flow condition. Part 2 of the paper presents a computational study of the experimental turbine cascade as discussed in Part 1. Numerical calculations were carried out for this case using an unsteady Navier-Stokes solver. The Baldwin-Lomax mixing length model was adopted for turbulence closure. The boundary layers on blade surfaces were either assumed to be fully turbulent or transitional with the unsteady transition subject to a quasi-steady laminar separation bubble model. The comparison between the computations and the experiment were generally quite satisfactory, except in the regions with the flow separation. It was shown that the behaviour of the short-bubble on the suction surface could be reasonably accounted for by using the quasi-steady bubble transition model. The calculation also showed that there was a more apparent mesh dependence of the results in the regions of flow separation. Two different kinds of numerical tests were carried out to check the linearity of the unsteady flow and therefore the validity of the Influence Coefficient method. Firstly calculations using the same configurations as in the experiment were performed with different oscillating amplitudes. Secondly calculations were performed with a tuned cascade model and the results were compared with those using the Influence Coefficient method. The present work showed that nonlinear effect was quite small, even though for the most severe case in which the separated flow region covered about 60% of blade pressure surface with a large movement of the reattachment point. It seemed to suggest that the linear assumption about the unsteady flow behaviour should be adequately acceptable for situations with bubble type flow separation similar to the present case.

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