scholarly journals The Effect of Aspect Ratio on Compressor Performance

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Ho-On To ◽  
Robert J. Miller
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Pressure Rise ◽  
Rate Of Change ◽  
Maximum Efficiency ◽  
Order Model ◽  
Aspect Ratios ◽  
Blade Thickness ◽  
Compressor Performance ◽  
Low Order

Abstract The optimum aspect ratio at which maximum efficiency occurs is relatively low, typically between 1 and 1.5. At these aspect ratios, inaccuracies inherently exist in the decomposition of the flow field into freestream and endwall components due to the absence of a discernible freestream. In this paper, a unique approach is taken: a “linear repeating stage” concept is used in conjunction with a novel way of defining the freestream flow. Through this approach, physically accurate decomposition of the flow field for aspect ratios as low as ∼0.5 can be achieved. This ability to accurately decompose the flow leads to several key findings. First, the endwall flow is found to be dependent on static pressure rise coefficient and endwall geometry, but independent of the aspect ratio. Second, the commonly accepted relationship that endwall loss coefficient varies inversely with the aspect ratio is shown to be physically inaccurate. Instead, a new term, which the authors refer to as the “effective aspect ratio,” should replace the term “aspect ratio.” Moreover, not doing so can result in efficiency errors of ∼0.6% at low aspect ratios. Finally, there exists a low aspect ratio limit below which the two endwall flows interact causing a large separation to occur along the span. From these findings, a low-order model is developed to model the effect of varying aspect ratio on compressor performance. The last section of the paper uses this low-order model and a simple analytical model to show that to a first order, the optimum aspect ratio is just a function of the loss generated by the endwalls at zero clearance and the rate of change in profile loss due to blade thickness. This means that once the endwall configuration has been selected, i.e., cantilever or shroud, the blade thickness sets the optimum aspect ratio.

scholarly journals The Effect of Aspect Ratio on Compressor Performance

2015 ◽  
Author(s):  
Ho-On To ◽  
Robert J. Miller
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Order Model ◽  
Aspect Ratios ◽  
Blade Thickness ◽  
Rate Of Increase ◽  
Unique Approach ◽  
Compressor Performance ◽  
Relationship Of ◽  
Low Order

This paper considers the effect of aspect ratio on compressor performance. It is shown that the aspect ratio at which max efficiency occurs is relatively low, typically between 1 and 1.5. At these aspect ratios, decomposition of the flow field into freestream and endwall flows becomes difficult. In this paper, a unique approach is taken; McKenzie’s ‘linear repeating stage’ concept is used and a novel way of defining freestream flow is proposed. Through these simplifications and methods, physically accurate decomposition of the flow field for aspect ratios as low as ∼0.7 can be achieved. This ability to accurately decompose the flow field leads to two key findings. Firstly, the commonly accepted relationship of endwall loss coefficient varying inversely with aspect ratio is inaccurate. Instead, a new term, which the authors refer to as ‘effective aspect ratio’, should replace aspect ratio. It is shown that not doing so can result in efficiency errors of ∼0.6% at low aspect ratios. Secondly, there exists a low aspect ratio limit below which the two endwall flows interact causing a large separation to occur along the span. From these findings, a low order model is developed to model the effect of varying aspect ratio on performance. The last section of this paper uses this low order model as well as a simple analytical model to show that to a first order, the optimum aspect ratio is just a function of the loss generated by the endwalls at zero clearance and the rate of increase in profile loss due to blade thickness. This means that once the endwall configuration has been selected i.e. cantilever or shroud, the blade thickness sets the optimum aspect ratio.

Flow Measurements in a Nozzle Guide Vane Passage With a Low Aspect Ratio and Endwall Contouring

2000 ◽  
Author(s):  
Steven W. Burd ◽  
Terrence W. Simon
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Guide Vane ◽  
Flow Measurements ◽  
Vast Number ◽  
Aspect Ratios ◽  
Nozzle Guide Vane ◽  
Endwall Contouring ◽  
Nozzle Guide

The vast number of turbine cascade studies in the literature has been performed in straight-endwall, high-aspect-ratio, linear cascades. As a result, there has been little appreciation for the role of, and added complexity imposed by, reduced aspect ratios. There also has been little documentation of endwall profiling at these reduced spans. To examine the role of these factors on cascade hydrodynamics, a large-scale nozzle guide vane simulator was constructed at the Heat Transfer Laboratory of the University of Minnesota. This cascade is comprised of three airfoils between one contoured and one flat endwall. The geometries of the airfoils and endwalls, as well as the experimental conditions in the simulator, are representative of those in commercial operation. Measurements with hot-wire anemometry were taken to characterize the flow approaching the cascade. These measurements show that the flow field in this cascade is highly elliptic and influenced by pressure gradients that are established within the cascade. Exit flow field measurements with triple-sensor anemometry and pressure measurements within the cascade indicate that the acceleration imposed by endwall contouring and airfoil turning is able to suppress the size and strength of key secondary flow features. In addition, the flow field near the contoured endwall differs significantly from that adjacent to the straight endwall.

Performance Prediction for High Turning Low Aspect Ratio Stator Cascades in the Transonic Regime

1970 ◽  
Vol 92 (4) ◽  
pp. 390-398
Author(s):  
H. F. L. Griepentrog
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Flow Field ◽  
Performance Prediction ◽  
Transonic Flow ◽  
Secondary Flows ◽  
Compressor Stage ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Boundary Layer Interaction

This paper describes a method for the prediction of the transonic flow field in a high solidity, high turning cascade, suitable for use as stator of a shock-in-rotor supersonic compressor stage. Effects of shock boundary layer interaction is taken into account by empirical correlation, valid for blade aspect ratios below unity. Use of partial slots for reduction of the secondary flows is briefly discussed and a correlation on slot efficiency is presented.

Experimental Investigation of Non-Axisymmetrical Flow Control in a Low Speed Axial Compressor

2009 ◽  
Author(s):  
Huabing Jiang ◽  
Yajun Lu ◽  
Wei Yuan ◽  
Qiushi Li
Keyword(s):  
Flow Field ◽  
Flow Control ◽  
Total Pressure ◽  
Pressure Rise ◽  
Separated Flow ◽  
Experimental Results ◽  
Stall Margin ◽  
Casing Treatment ◽  
Compressor Performance ◽  
Compressor Efficiency

The non-axisymmetric feature of the compressor separated flow field should be considered when flow control technology is utilized to improve compressor performance. An experiment is performed to investigate the effectiveness of non-axisymmetric flow control using arc curve skewed slot casing treatment in the paper. A simplified non-axisymmetric excitation model is presented with variable circumferential excitation extent and location. FFT analysis results indicate that the frequency spectrum of the non-axisymmetric excitation is similar with that of the whole circumferential excitation. The non-axisymmetric excitation possesses the same dominate frequency, smaller amplitude and wider frequency bandwidth compared to the whole circumferential excitation. A simplified circumferential non-axisymmetric arc curve skewed slot casing treatment is utilized to perform non-axisymmetric excitation on the separated flow field of a low speed single stage axial compressor under both uniform and distorted inlet conditions. Experimental results indicate that the non-axisymmetric slotted casing treatment presents strong flow control capability, which could improve compressor efficiency, total pressure rise coefficient and stall margin. For the distorted inlet condition, the stall margin, total pressure rise and efficiency of the compressor are respectively improved by 47.4%, 12.7% and 0.7% compared to the solid casing, and the compressor efficiency is improved by 1.4% compared to the whole circumferential excitation. For uniform inlet condition, the non-axisymmetric excitation can improve compressor efficiency by 1.0% and 1.5% respectively compared to the solid casing and the whole circumferential excitation. The whole circumferential excitation can also improve the compressor total pressure rise coefficient and stall margin, on the contrary, it decreases compressor efficiency. As a result, the non-axisymmetric slotted casing treatment can achieve more excellent compressor performance than the whole circumferential excitation does. Experimental results also indicate that the circumferential extent and location of the non-axisymmetric excitation can influence the effectiveness of the non-axisymmetric excitation. The best compressor performance can be achieved only when the non-axisymmetric excitation is tuned to match the asymmetric compressor separated flow field. Analysis on the experimental results indicates that compressor efficiency improvement achieved with the non-axisymmetric excitation can not simply attribute to the flow loss reduction induced by fewer casing slots. The flow loss reduction within undistorted sector, the circumferential flow exchange and the dynamic response induced by the non-axisymmetric excitation, the unsteady coupling between the non-axisymmetric excitation and the separated flow field might be the key flow factors to influence the compressor flow field structure, and hence influence the compressor performance.

Experimental Study on the Performance and Pressure Fluctuations of a Regenerative Gas Blower for Different Design Parameters

2011 ◽  
Author(s):  
Younghoon Kim ◽  
Shin Hyoung Kang ◽  
Yonggyu Noh
Keyword(s):  
Pressure Fluctuation ◽  
Pressure Fluctuations ◽  
Fast Response ◽  
Fuel Cell Vehicle ◽  
Maximum Efficiency ◽  
Design Parameters ◽  
Pressure Transducers ◽  
Total Enthalpy ◽  
Aspect Ratios ◽  
Blade Thickness

A regenerative gas blower design for fuel cell vehicle is presented. Two issues studied concern non-dimensional performance characteristics under various design parameters and the noise of the blower due to unsteady pressure fluctuation. Non-dimensional performance curves were measured at various rotating speeds and gas mixture ratios. Blower models using different design parameters such as the stripper angle, blade aspect ratios and blade thickness ratios were tested. The effects that aforementioned parameters had on performance were investigated. Surface pressure fluctuations were measured in the channel close to both ends of the stripper using fast-response pressure transducers. A sharp blade increases the maximum isentropic total enthalpy coefficient and the maximum efficiency because the pressure loss coefficient of the circulatory flow is reduced. A small stripper angle enhanced the maximum isentropic total enthalpy coefficient and the maximum efficiency because working sections was lengthened. The enlarged stripper angle and the low pressure difference across the stripper reduce the magnitude of pressure fluctuation at the blade passing frequency.

scholarly journals Effects of Non-Axisymmetric Tip Clearance on Axial Compressor Performance and Stability

1997 ◽  
Author(s):  
M. B. Graf ◽  
T. S. Wong ◽  
E. M. Greitzer ◽  
F. E. Marble ◽  
C. S. Tan ◽  
...  
Keyword(s):  
Steady State ◽  
Theoretical Model ◽  
Peak Pressure ◽  
Good Description ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Tip Clearance ◽  
Maximum Efficiency ◽  
Stall Margin ◽  
Compressor Performance

The effects of circumferentially non-uniform lip clearance on axial compressor performance and stability have been investigated experimentally and analytically. A theoretical model for compressor behavior with non-axisymmetric tip clearance has been developed and used to design a series of first-of-a-kind experiments on a four-stage, low speed compressor. The experiments and computational results together show clearly the central physical features and controlling parameters of compressor response to non-axisymmetric lip clearance. It was found that the loss in stall margin was more severe than that estimated based on average clearance. The stall point was, in fact, closer to that obtained with uniform clearance at the maximum clearance level. The circumferential length scale of the tip clearance (and accompanying flow asymmetry) was an important factor in determining the stall margin reduction. For the same average clearance, the loss in peak pressure rise was 50% higher for an asymmetry with fundamental wavelength equal to the compressor circumference than with wavelength equal to one-half the circumference. The clearance asymmetry had much less of an effect on peak efficiency; the measured maximum efficiency decrease obtained was less than 0.4 percent compared to the 8% decrease in peak pressure rise due to the asymmetric clearance. The efficiency penalty due to non-axisymmetric tip clearance was thus close to that obtained with a uniform clearance at the circumferentially-averaged level. The theoretical model accurately captured the decreases in both steady-state pressure rise and stable operating range which are associated with clearance asymmetry. It also gave a good description of the observed trends of (i) increasing velocity asymmetry with decreasing compressor flow, and (ii) decreasing effect of clearance asymmetry with decreasing dominant wavelength of the clearance distribution. The time resolved data showed that the spatial structure of the pre-stall propagating disturbances in the compressor annulus was well represented and that the stability limiting process could be linked to the unsteady structure of these disturbance modes. The model was also utilized for parametric studies to define how compressor performance and stability is affected by the circumferential distribution of clearance, steady-state compressor pressure-rise characteristic, and system dynamic parameters. Sensitivity to clearance asymmetry was found to fall off strongly with the (asymmetry-related) reduced frequency and to increase with peak pressure rise and increasing curvature of the characteristic near the peak.

Heat Release Response to Forced Flow Oscillations of a Low-Order Modelled Laboratory Scale Dump Combustor

2015 ◽  
Author(s):  
Alessandro Orchini ◽  
Matthew P. Juniper
Keyword(s):  
Flow Field ◽  
Heat Release ◽  
Bluff Body ◽  
Forced Flow ◽  
Mean Flow ◽  
Order Model ◽  
Qualitative Comparison ◽  
Velocity Fluctuations ◽  
Dump Combustor ◽  
Low Order

In this study we investigate the heat release response to forced harmonic velocity fluctuations of a bluff body dump combustor. We use the kinematic G-equation as a low-order model for the flame and heat release dynamics. The geometry considered is based on an experimental setup developed by R. Balachandran and widely investigated in the literature, and we look for a qualitative comparison with experimental and numerical results. We model the flow field dynamics adapting the well-known travelling wave model, which was originally developed for conical flames, to the case of a bluff-body stabilized flame in a non-uniform mean flow field. We impose velocity fluctuations at the dump plane at various frequencies and amplitudes and we integrate the nonlinear flame and heat release dynamics. Results show that the model qualitatively reproduces the kinematic behaviour observed in the experiments, although some major quantitative differences are found. We conclude by discussing our results, and adjustments that could be introduced in future in the low-order model in order to improve it.

Analysis of the Losses in an Axial Fan With Small Blade Aspect Ratios Using CFD-Technique and Laser Doppler Anemometry

2020 ◽  
Author(s):  
Anika Theis ◽  
Thomas Reviol ◽  
Martin Böhle
Keyword(s):  
Aspect Ratio ◽  
Laser Doppler Anemometry ◽  
Axial Flow ◽  
Axial Fan ◽  
Laser Technique ◽  
Ratio Distribution ◽  
Aspect Ratios ◽  
Blade Thickness ◽  
Spacing Ratio ◽  
3D Simulation Model

Abstract In this contribution an axial flow fan is designed with four different blade aspect ratios. These four blade aspect ratios are obtained by using four different numbers of blades. The blade aspect ratios are varied between 0.2 and 0.6. For this investigation the thickness ratio distribution and the spacing ratio are kept constant in the design process for all four blade aspect ratios. This means, the blade thickness, the spacing and the blade chord are adjusted for every blade aspect ratio. Analysing low aspect ratios is challenging. Previous literature treating compressors suggests that at low aspect ratio the secondary losses and the freestream losses combine, making it difficult to separate the profile loss from the secondary flow losses. An approach to quantifying profile losses at the midspan of the blades for blade aspect ratios lower than 0.5, 2D simulations at the midspan are carried out for supplementary examination. The Reynolds number of all investigations is related to the chord length of each blade. It is varied from 2.38 × 105 to 7.13 × 105. During the survey, the same stator with a constant blade aspect ratio as well as a constant spacing ratio is used. In this contribution, LDA is applied as experimental method. Transient numerical simulations are performed for a full 3D simulation model to obtain a detailed view into the machine. Because of the low Reynolds numbers, the k-ω-SST transition model with the intermittency function is applied. With both methods, the flow is investigated on different planes inside the fan. The velocity distribution on the planes is analysed and compared to the transient simulation results. In the boundary layer, the velocity is resolved as well using the laser technique.

Scaling of Flow Characteristics and Power Consumption With Profile Height for Miniature Centrifugal Fans

2007 ◽  
Author(s):  
P. A. Walsh ◽  
V. Egan ◽  
R. Grimes ◽  
E. Walsh
Keyword(s):  
Aspect Ratio ◽  
Power Consumption ◽  
Flow Rate ◽  
Scaling Laws ◽  
Flow Characteristics ◽  
Pressure Rise ◽  
Maximum Flow ◽  
Aspect Ratios ◽  
Low Profile ◽  
Centrifugal Fans

This paper addresses issues that relate to downscaling the height of centrifugal fans for application in low profile technologies, such as the cooling of portable power electronics. The parameters studied throughout the paper include flow rate, pressure rise and power consumption characteristics. The former two of these are measured using a fan characterization rig and the latter by directly measuring the power supplied to the fan. These are studied for fans ranging in diameter from 15 to 30mm and with profile heights ranging from 0.3mm to 15mm. It is found that all of the phenomena encountered are best described in terms of fan aspect ratio. Overall, the results show that the conventional scaling laws cannot be accurately applied when the blade profile alone is being scaled. Indeed the only parameter that was observed to be accurately predicted by the scaling laws was the pressure rise attainable but was only accurate for fan aspect ratios greater than 0.17. Below this, the measured pressure rise characteristics fell logarithmically toward zero. The results also showed that there is no advantage to using fans with aspect ratio greater than 0.3. This was because the maximum flow rate was achieved at this aspect ratio and decreased slightly as it was further increased. Overall, the scaling phenomena described throughout this paper are invaluable to designer of efficient low profile cooling solutions that are to incorporate such fans.

Numerical Investigation on Effect of Aspect Ratio of Axisymmetric Circumferential Groove Casing Treatment Coupled to a Transonic Axial Flow Compressor Stage

2015 ◽  
Author(s):  
Nishit J. Mehta ◽  
Dilipkumar Bhanudasji Alone ◽  
Harish S. Choksi
Keyword(s):  
Aspect Ratio ◽  
Flow Field ◽  
Flow Behavior ◽  
Geometrical Parameters ◽  
Compressor Stage ◽  
Casing Treatment ◽  
Transonic Compressor ◽  
Circumferential Groove ◽  
Aspect Ratios ◽  
The Impact

While the effects of axisymmetric casing treatment on performance of an axial compressor stage have been extensively studied numerically as well as experimentally, the major geometrical parameters which govern these effects have been identified. Studies are now focused on understanding how each of these parameters individually impacts the performance of a casing treatment. The present work aims to study the impact on performance of casing treatment geometry when aspect ratio of the grooves is varied in a circumferential groove casing treatment. The compressor geometry chosen for this study has design characteristics of a transonic compressor stage. Flow field solutions were derived for baseline model by solving steady state 3-D Reynolds-Averaged Navier-Stokes (RANS) equations for three grid densities and the grid independence was proved. The basic casing treatment geometry has 10 circumferential grooves of width 4mm and axial spacing of 2mm between each groove. The aspect ratio was varied by changing the depth of the grooves in each case. These casing treatment geometries were superimposed over the rotor domain with the grooves extending over the entire blade tip chord and flow field solutions were again obtained for various aspect ratios of grooves. These results depict improvement in the range of operation in terms of mass flow rate. Results also show that the aspect ratio of the grooves significantly influences the overall effectiveness of casing treatment on the performance of compressor stage. Improvement in overall compressor efficiency is noted with lower aspect ratio casing treatments when compared to those with higher aspect ratios, however, the range improvement is higher with higher aspect ratios. It is also observed that, after a certain depth of grooves is reached, there is no significant improvement in performance on further increasing the depth and hence the aspect ratio. Post processing results of the flow solutions are presented which confirm the trends and show that the flow behavior near rotor tip governs this effect.

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