Exploring the Presence of Pressure Waves in Axial Compressor Cascades

2020 ◽  
Author(s):  
John Leggett ◽  
Richard Sandberg
Keyword(s):  
Free Stream ◽  
Axial Compressor ◽  
Pressure Waves ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Trailing Edge ◽  
Surface Transition

Abstract The presence of pressure waves in an axial compressor cascade are ubiquitous and have been known and investigated for some time. Much of the work to date focuses on compressor acoustics and vibration, which is largely due to wake blade interactions and trailing edge shedding. However, it has been shown on free aerofoils that pressure waves can be produced from volume sources, such as separation, at non-negligible amplitudes. The work presented here highlights the presence of pressure waves emanating from the suction surface transition of a NACA 65 axial compressor cascade, and briefly investigates and details the influence different free-stream disturbances have on the frequency of the pressure waves produced.

Boundary Layer Control of an Axial Compressor Cascade Using Nonconventional Vortex Generators

2015 ◽  
Author(s):  
Ahmed M. Diaa ◽  
Mohammed F. El-Dosoky ◽  
Mahmoud A. Ahmed ◽  
Omar E. Abdel-Hafez
Keyword(s):  
Boundary Layer ◽  
Passive Control ◽  
Axial Compressor ◽  
Vortex Generators ◽  
Boundary Layer Control ◽  
Geometrical Parameters ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Flow Equations ◽  
Layer Control

Boundary layer control plays a decisive role in controlling the performance of axial compressor. Vortex generators are well known as passive control devices of the boundary layer. In the current study, two nonconventional types of vortex generators are used and their effects are investigated. The used vortex generators are doublet, and wishbone. Three dimensional turbulent compressible flow equations through an axial compressor cascade are numerically simulated. Comparisons between cascade with and without vortex generators are performed to predict the effect of inserting vortex generator in the overall performance of the axial compressor. Results indicate that using vortex generators leads to eliminate or delay the separation on the blade suction surface, as well as the endwall. Furthermore, the effects of the vortex generators and their geometrical parameters on the aerodynamic performance of the cascade are documented. In conclusion, while the investigated vortex generators cause a slight increase in the total pressure loss, a significant reduction in the skin friction coefficient at the bottom endwall is found. This reduction is estimated to be about 46% using doublet and 32% using wishbone.

Effect of Trailing Edge Crenulation on the Performance and Stall Margin of a Transonic Axial Compressor

2013 ◽  
Author(s):  
S. Subbaramu ◽  
Quamber H. Nagpurwala ◽  
A. T. Sriram
Keyword(s):  
Beneficial Effect ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Compressor Cascade ◽  
Trailing Edge ◽  
Stall Margin ◽  
Positive Effects ◽  
Compressor Rotor ◽  
Transonic Axial Compressor

This paper deals with the numerical investigations on the effect of trailing edge crenulation on the performance of a transonic axial compressor rotor. Crenulation is broadly considered as a series of small notches or slots at the edge of a thin object, like a plate. Incorporating such notches at the trailing edge of a compressor cascade has shown beneficial effect in terms of reduction in total pressure loss due to enhanced mixing in the wake region. These notches act as vortex generators to produce counter rotating vortices, which increase intermixing between the free stream flow and the low momentum wake fluid. Considering the positive effects of crenulation in a cascade, it was hypothesized that the same technique would work in a rotating compressor to enhance its performance and stall margin. However, the present CFD simulations on a transonic compressor rotor have given mixed results. Whereas the peak total pressure ratio in the presence of trailing edge crenulation reduced, the stall margin improved by 2.97% compared to the rotor with straight edge blades. The vortex generation at the crenulated trailing edge was not as strong as reported in case of linear compressor cascade, but it was able to influence the flow field in the rotor tip region so as to energize the low momentum end-wall flow in the aft part of the blade passage. This beneficial effect delayed flow separation and allowed the mass flow rate to be reduced to still lower levels resulting in improved stall margin. The reduction in pressure ratio with crenulation was surprising and might be due to increased mixing losses downstream of the blade.

Effect of Surface Roughness Location and Reynolds Number on Compressor Cascade Performance

2010 ◽  
Author(s):  
Seung Chul Back ◽  
Garth V. Hobson ◽  
Seung Jin Song ◽  
Knox T. Millsaps
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Leading Edge ◽  
Suction Side ◽  
Pressure Side ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Trailing Edge ◽  
Blade Loading ◽  
Linear Compressor Cascade

An experimental investigation has been conducted to characterize the influence of surface roughness location and Reynolds number on compressor cascade performance. Flow field surveys have been conducted in a low-speed, linear compressor cascade. Pressure, velocity, and flow angles have been measured via a 5-hole probe, pitot probe, and pressure taps on the blades. In addition to the entirely smooth and entirely rough blade cases, blades with roughness covering the leading edge; pressure side; and 5%, 20%, 35%, 50%, and 100% of suction side from the leading edge have been studied. All of the tests have been done for Reynolds number ranging from 300,000 to 640,000.Cascade performance (i.e. blade loading, loss, and deviation) is more sensitive to roughness on the suction side than pressure side. Roughness near the trailing edge of suction side increases loss more than that near the leading edge. When the suction side roughness is located closer to the trailing edge, the deviation and loss increase more rapidly with Reynolds number. For a given roughness location, there exists a Reynolds number at which loss begins to visibly increase. Finally, increasing the area of rough suction surface from the leading edge reduces the Reynolds number at which the loss coefficient begins to increase.

Three-Dimensional Turbulent Flow Field Downstream of a Single-Stage Axial Compressor Rotor

2000 ◽  
Author(s):  
Hongwei Ma ◽  
Haokang Jiang
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Mass Flow ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Single Stage ◽  
Suction Surface ◽  
Trailing Edge ◽  
Rotor Wake ◽  
Compressor Rotor

This paper reports an experimental investigation of the three-dimensional turbulent flow downstream of a single-stage axial compressor rotor. The flow fields were measured at two axial locations in the rotor-stator gap at different mass-flow conditions. Both hot-wire probe and fast-response pressure probe were employed to survey the flow structure. At the design condition, substantial flow blockage, turbulence, loss and aerodynamic noise mainly occur in the tip mid-passage, the rotor wake and at the hub corner of the suction surface. The radial component is the highest of the three turbulence intensities at 15% axial chord downstream of the trailing edge. With the flow downstream, the radial turbulence components decay fast. Interactions of the tip leakage vorticities and the rotor wake are found at 30% axial chord downstream of the trailing edge. With the mass-flow decrease, the turbulence intensities and shear stresses become stronger, while the radial components increase fast. The flow separation and tangential migration of the low-energy fluids at the tip corner of the suction surface play an important role in the tip flow field at a low mass-flow condition.

Three-Dimensional Turbulent Flow of the Tip Leakage Vortex in an Axial Compressor Rotor Passage

2000 ◽  
Author(s):  
Hongwei Ma ◽  
Haokang Jiang
Keyword(s):  
Turbulent Flow ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Radial Component ◽  
Reynolds Stresses ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Compressor Rotor

Three-dimensional turbulent flow of the tip leakage vortex in a single-stage axial compressor rotor passage is studied using a 3-Component Laser Doppler Velocimetry. The measurement results indicate that the tip leakage vortex originates at about 10% axial chord, 8% pitch away from the suction surface, and becomes strongest at about 30% chord. With the flow downstream, the vortex core moves toward the pressure surface and to a lower radial location, leading to substantial flow mixing, blockage and turbulence in the tip region. The radial component of turbulence intensities is found to be the highest while the axial-radial component of Reynolds stresses is the largest. Breakdown of the leakage vortex occurs inside the rear rotor passage, which makes the flow more turbulent in a wider region downstream. This viewpoint is confirmed by the measurements of unsteady static pressure on the casing wall. Breakdown of a leakage vortex is observed clearly in a compressor cascade with a small clearance. Unsteady interactions of the broken vorticities and the suction surface’s boundary layer are shown obviously inside the downstream passage.

scholarly journals Wake Mixing Improvements in a Linear Compressor Cascade With Crenulated Trailing Edges

1990 ◽  
Author(s):  
J. L. Veesart ◽  
P. I. King ◽  
W. C. Elrod ◽  
A. J. Wennerstrom
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Total Pressure Loss ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Trailing Edge ◽  
Turbine Engine ◽  
Pressure Surface ◽  
Trailing Edges ◽  
Linear Compressor Cascade

Trailing edge crenulations offer one possible way of energizing the trailing edge wakes from a gas turbine engine compressor blade by creating small vortices as a result of the pressure differential between the suction surface and pressure surface. The effect of crenulated trailing edges on wake dissipation and mixed-out total pressure loss in a linear, subsonic, compressor cascade was investigated for three low aspect ratio blade configurations: one with no crenulations and two others with large and small crenulation patterns, respectively. The effect of crenulations was to improve the wake mixing and reduce the velocity deficit. larger crenulations dissipated the wake most rapidly, and both crenulation configurations offered an improvement in total pressure loss and some improvement in flow turning.

scholarly journals Loss Prediction in an Axial Compressor Cascade at Off-Design Incidences With Free Stream Disturbances Using Large Eddy Simulation

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
John Leggett ◽  
Stephan Priebe ◽  
Aamir Shabbir ◽  
Vittorio Michelassi ◽  
Richard Sandberg ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Free Stream ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Boundary Layer Transition ◽  
Compressor Cascade ◽  
Free Stream Turbulence ◽  
Eddy Simulation ◽  
Profile Losses ◽  
Large Eddy

Axial compressors may be operated under off-design incidences due to variable operating conditions. Therefore, a successful design requires accurate performance and stability limits predictions under a wide operating range. Designers generally rely both on correlations and on Reynolds-averaged Navier–Stokes (RANS), the accuracy of the latter often being questioned. The present study investigates profile losses in an axial compressor linear cascade using both RANS and wall-resolved large eddy simulation (LES), and compares with measurements. The analysis concentrates on “loss buckets,” local separation bubbles and boundary layer transition with high levels of free stream turbulence, as encountered in real compressor environment without and with periodic incoming wakes. The work extends the previous research with the intention of furthering our understanding of prediction tools and improving our quantification of the physical processes involved in loss generation. The results show that while RANS predicts overall profile losses with good accuracy, the relative importance of the different loss mechanisms does not match with LES, especially at off-design conditions. This implies that a RANS-based optimization of a compressor profile under a wide incidence range may require a thorough LES verification at off-design incidence.

LES Loss Prediction in an Axial Compressor Cascade at Off-Design Incidences With Free Stream Disturbances

2017 ◽  
Author(s):  
John Leggett ◽  
Stephan Priebe ◽  
Aamir Shabbir ◽  
Richard Sandberg ◽  
Edward Richardson ◽  
...  
Keyword(s):  
Free Stream ◽  
Axial Compressor ◽  
Quantitative Prediction ◽  
Compressor Cascade ◽  
Physical Processes ◽  
Free Stream Turbulence ◽  
Eddy Simulation ◽  
Profile Losses ◽  
Large Eddy ◽  
Loss Prediction

It is well known that an axial compressor cascade will exhibit variation in loss coefficient, described as a loss bucket, when run over a sweep of incidences, and that higher levels of free stream turbulence are likely to suppress separation bubbles and cause earlier transition (see e.g. [23]). However, it remains difficult to achieve accurate quantitative prediction of these changes using numerical simulation, particularly at off-design conditions, without the added computational expense of using eddy-resolving techniques. The aim of the present study is to investigate profile losses in an axial compressor under such conditions using wall-resolved Large Eddy Simulation (LES) and RANS. The work extends on previous work by Leggett et al.[11] with the intention of furthering our understanding of loss prediction tools and improving our quantification of the physical processes involved in loss generation. The results show that while RANS predicts losses with good accuracy the breakdown of these losses are attributed to different processes, meaning that optimisation of a compressor cascade profile, based solely on RANS, may be hard to achieve.

Influence of endwall slotted injection on performance and flow physics in a compressor cascade

2020 ◽  
pp. 095765092094653
Author(s):  
Zhiyuan Cao ◽  
Cheng Song ◽  
Bo Liu ◽  
Limin Gao
Keyword(s):  
Flow Control ◽  
Leading Edge ◽  
Loss Coefficient ◽  
Control Methods ◽  
Compressor Cascade ◽  
Control Effect ◽  
Suction Surface ◽  
Trailing Edge ◽  
Corner Separation ◽  
Axial Location

Air injection is an effectively methodology to suppress flow separation and to improve blade loading of airfoils and compressors. In order to remove corner separations in a cascade, investigation of endwall slotted injection was carried out numerically in this study. Based on endwall slot schemes of other flow control methods, six different endwall slots were designed, aiming at revealing the axial location effect and pitchwise location effect. For each endwall slot, numerical simulations were performed with six different injection directions to uncover the injection direction effect. Results showed that endwall slotted injection can effectively remove the corner separation. The overall loss coefficient and endwall loss coefficient of the cascade were reduced by 10.3% and 36.8% at most, respectively. Injection from leading edge and mid-chord can reduce endwall loss; however, the optimal axial location of endwall slot is near the trailing edge, where the corner separation is located. Different with other flow control methods, in general, the optimal pitchwise location of endwall slot is not close to suction surface but 0.16 pitch away from it. Injection near the suction surface is more sensitive to injection direction compared with injection at 0.16 pitch away from suction surface. Injection with velocity components both downstream and toward suction surface promises optimal control effect on corner separation. However, at mid-span, trailing edge separation is deteriorated and the flow turning angle is reduced, the flow mechanism being that the low-momentum fluid migrates along spanwise.

Effect of Boundary Layer Suction on the Corner Separation in a Highly Loaded Axial Compressor Cascade

2020 ◽  
Author(s):  
Tian Liang ◽  
Bo Liu ◽  
Stephen Spence
Keyword(s):  
Boundary Layer ◽  
Axial Compressor ◽  
Compressor Cascade ◽  
Flow Uniformity ◽  
Suction Surface ◽  
Flow Rates ◽  
Corner Separation ◽  
Boundary Layer Suction ◽  
End Wall ◽  
Suction Flow

Abstract Control of corner separation in axial compressor blade rows has attracted much interest due to its potential to improve compressor efficiency and the energy utilization in turbomachinery. This paper investigates the effectiveness and mechanisms of boundary layer suction in controlling the corner separation of a highly loaded axial compressor cascade. Numerical simulations have been carried out to investigate the effect of different suction schemes on the loss downstream of the cascade and the change in incidence characteristics with the variation of the suction flow rate. The results show that the effectiveness of flow suction in controlling the flow separation depends heavily on the proportion of the blade for which it is applied. It was found that suction along part of the blade span on the suction surface could effectively remove the separation at the region of the span influenced by the suction slot. However, this resulted in a deterioration of the flow field at other parts of the span. The full span suction scheme on the suction surface not only eliminated the separation of the boundary layer in the middle of the blade, but also significantly improved the flow uniformity near the end-wall. Despite the improvement in flow uniformity using the full-span suction scheme, a three-dimensional (3D) corner separation still existed due to the strong cross-passage pressure gradient. To improve the flow field uniformity further, two combined suction schemes with one spanwise slot on the suction surface and another slot on the end-wall were designed in order to fully remove both the separated flow on the blade suction surface and the 3D corner separation. It was found that the total pressure loss coefficient was reduced significantly by 63.8% with suction flow rates of 1.88% and 0.82% for the slots on the suction surface and the end-wall respectively. Further work showed that the behavior of the loss coefficient is different as the combination of suction flow rates is changed for different incidence. The cascade loss at high incidence operation can be more effectively reduced with suction control on the end-wall. When implementing combined suction, it is necessary to determine the best combination of suction flow rate according to the incidence level.

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