Non-Axisymmetric End Wall Profiling in Transonic Compressors—Part II: Design Study of a Transonic Compressor Rotor Using Non-Axisymmetric End Walls—Optimization Strategies and Performance

2009 ◽  
Author(s):  
Steffen Reising ◽  
Heinz-Peter Schiffer
Keyword(s):  
Secondary Flow ◽  
Total Pressure ◽  
Cfd Simulation ◽  
Pressure Ratio ◽  
Cross Flow ◽  
Secondary Flows ◽  
Transonic Compressor ◽  
End Wall ◽  
Total Pressure Ratio ◽  
Isentropic Efficiency

Secondary flows involving cross flow at high stage loading in modern axial compressors contribute significantly to efficiency limits. This paper summarizes an approach to control end wall flow using non-axisymmetric end walls. The challenge is to find the optimal non-axisymmetric end wall shape that results in the largest gain in performance. An automated multi-objective optimizer connected to a 3-D RANS flow solver was used to design the end wall contour. The process chain was applied to the rotor hub end wall of Configuration I of the Darmstadt Transonic Compressor. Several optimization strategies involving different objective functions to be minimized and the corresponding performances were compared. The parameters considered within the optimization process were isentropic stage efficiency, pressure loss in the rotor, throat area and secondary kinetic energy (SKE). A parameter variation was undertaken, leading to the following observations: Strong penalties on SKE at the rotor outlet and moderate penalties on isentropic efficiency, throat area and pressure ratio led to the best design. Isentropic efficiency could be raised by 0.12%, SKE at the rotor exit was reduced while the total pressure ratio of the stage remained constant. Strong penalties on efficiency and pressure ratio, a moderate one on throat area and a small one on SKE at the rotor outlet all led to a smaller increase in efficiency: 0.06%. On the other hand, a slight raise in the total pressure ratio could be achieved. A third optimization, eliminating the restriction on the throat area, was carried out to see which benefit in performance could be achieved without this geometrical restriction. Since the throat areas of all optimized geometries differ slightly from the datum value, an estimation was derived to see the extent to which the end wall profiling and cross section enlargement contribute to the improvements. Finally, a method to display secondary flows in turbomachinery is introduced. A second CFD simulation is used to calculate the primary flow where the hub end wall is defined as an Euler wall to avoid the end wall boundary layer and so eliminate the cause for some of the secondary flow mechanisms. This method clearly shows how the characteristics of secondary flow can be positively influenced by using non-axisymmetric end walls.

Numerical Investigation on the Effects of Circumferential Coverage of Injection in a Transonic Compressor With Discrete Tip Injection

2014 ◽  
Author(s):  
Wei Wang ◽  
Wuli Chu ◽  
Haoguang Zhang ◽  
Yanhui Wu
Keyword(s):  
Total Pressure ◽  
Pressure Ratio ◽  
Time Lag ◽  
Three Dimensional ◽  
Stability Margin ◽  
Transonic Compressor ◽  
Blade Tip ◽  
Tip Injection ◽  
The Stability ◽  
Total Pressure Ratio

Discrete tip injection upstream of the rotor tip is an effective technique to extend stability margin for a compressor system in an aeroengine. The current study investigates the effects of injectors’ circumferential coverage on compressor performance and stability using time-accurate three-dimensional numerical simulations for multi passages in a transonic compressor. The percentage of circumferential coverage for all the six injectors ranges from 6% to 87% for the five investigated configurations. Results indicate that circumferential coverage of tip injection can greatly affect compressor stability and total pressure ratio, but has little influence on adiabatic efficiency. The improvement of compressor total pressure ratio is linearly related with the increasing circumferential coverage. The unsteady flow fields show that there exists a non-ignorable time lag of the injection effects between the passage inlet and outlet, and blade tip loading will not decline until the injected flow reaches the passage outlet. Stability improves sharply with the increasing circumferential coverage when the coverage is less than 27%, but increases flatly for the rest. It is proven that the injection efficiency which is a measurement of averaged blockage decrement in the injected region is an effective guideline to predict the stability improvement.

Experimental Investigation of Aspiration in a Multi-Stage High-Speed Axial-Compressor

2016 ◽  
Author(s):  
Jan Siemann ◽  
Ingolf Krenz ◽  
Joerg R. Seume
Keyword(s):  
Flow Field ◽  
Total Pressure ◽  
High Speed ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Reference Configuration ◽  
Corner Separation ◽  
Part Load ◽  
Total Pressure Ratio ◽  
Isentropic Efficiency

Reducing the fuel consumption is a main objective in the development of modern aircraft engines. Focusing on aircraft for mid-range flight distances, a significant potential to increase the engines overall efficiency at off-design conditions exists in reducing secondary flow losses of the compressor. For this purpose, Active Flow Control (AFC) by aspiration or injection of fluid at near wall regions is a promising approach. To experimentally investigate the aerodynamic benefits of AFC by aspiration, a 4½-stage high-speed axial-compressor at the Leibniz Universitaet Hannover was equipped with one AFC stator row. The numerical design of the AFC-stator showed significant hub corner separations in the first and second stator for the reference configuration at the 80% part-load speed-line near stall. Through the application of aspiration at the first stator, the numerical simulations predict the complete suppression of the corner separation not only in the first, but also in the second stator. This leads to a relative increase in overall isentropic efficiency of 1.47% and in overall total pressure ratio of 4.16% compared to the reference configuration. To put aspiration into practice, the high-speed axial-compressor was then equipped with a secondary air system and the AFC stator row in the first stage. All experiments with AFC were performed for a relative aspiration mass flow of less than 0.5% of the main flow. Besides the part-load speed-lines of 55% and 80%, the flow field downstream of each blade row was measured at the AFC design point. Experimental results are in good agreement with the numerical predictions. The use of AFC leads to an increase in operating range at the 55% part-load speed-line of at least 19%, whereas at the 80% part-load speed-line no extension of operating range occurs. Both speed-lines, however, do show a gain in total pressure ratio and isentropic efficiency for the AFC configuration compared to the reference configuration. Compared to the AFC design point, the isentropic efficiency ηis rises by 1.45%, whereas the total pressure ratio Πtot increases by 1.47%. The analysis of local flow field data shows that the hub corner separation in the first stator is reduced by aspiration, whereas in the second stator the hub corner separation slightly increases. The application of AFC in the first stage further changes the stage loading in all downstream stages. While the first and third stage become unloaded by application of AFC, the loading in terms of the De-Haller number increases in the second and especially in the fourth stage. Furthermore, in the reference as well as in the AFC configuration, the fourth stator performs significantly better than predicted by numerical results.

Aerodynamic Design and Analysis of a High Pressure Ratio Aspirated Compressor Stage

2000 ◽  
Author(s):  
Ali A. Merchant ◽  
Mark Drela ◽  
Jack L. Kerrebrock ◽  
John J. Adamczyk ◽  
Mark Celestina
Keyword(s):  
Boundary Layer ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Adverse Pressure Gradient ◽  
Compressor Stage ◽  
High Pressure Ratio ◽  
Total Pressure Ratio ◽  
Isentropic Efficiency

The pressure ratio of axial compressor stages can be significantly increased by controlling the development of blade and endwall boundary layers in regions of adverse pressure gradient by means of boundary layer suction. This concept is validated and demonstrated through the design and analysis of a unique aspirated compressor stage which achieves a total pressure ratio of 3.5 at a tip speed of 1500 ft/s. The aspirated stage was designed using an axisymmetric through-flow code coupled with a quasi three-dimensional cascade plane code with inverse design capability. Validation of the completed design was carried out with three-dimensional Navier-Stokes calculations. Spanwise slots were used on the rotor and stator suction surfaces to bleed the boundary layer with a total suction requirement of 4% of the inlet mass flow. Additional bleed of 3% was also required on the hub and shroud near shock impingement locations. A three-dimensional viscous evaluation of the design showed good agreement with the quasi three-dimensional design intent, except in the endwall regions. The three-dimensional viscous analysis predicted a mass averaged total pressure ratio of 3.7 at an isentropic efficiency of 93% for the rotor, and a mass averaged total pressure ratio of 3.4 at an isentropic efficiency of 86% for the stage.

Use of Inlet Guide Vanes for a Miniature Centrifugal Compressor

2005 ◽  
Author(s):  
Xiaoyi Li ◽  
Lei Zhou ◽  
Jay Kapat ◽  
Louis C. Chow
Keyword(s):  
Centrifugal Compressor ◽  
Total Pressure ◽  
High Speed ◽  
Cooling System ◽  
Pressure Ratio ◽  
Working Fluid ◽  
Guide Vanes ◽  
Inlet Guide Vanes ◽  
Total Pressure Ratio ◽  
Isentropic Efficiency

A novel design for a high-speed, miniature centrifugal compressor for a miniature RTBC (reverse turbo Brayton cycle) cryogenic cooling system is the focus of this paper. Due to the geometrical restriction imposed by the cryocooling system, the outer radius of the compressor is limited to 2.5 cm. Such a small compressor must rotate at a high speed in order to provide an acceptable pressure ratio. Miniature design precludes the use of inducers with large angles. In order to compensate for the absence of conventional inducers, the proposed design uses inlet guide vanes (IGV) that produce preswirl at the impeller inlet. IGV is followed by a radial impeller and an axial diffuser. The design speed for this compressor is 313,000 rpm for an overall static-to-total pressure ratio of 1.7 with helium as the working fluid for the compressor and the cryocooling system. The analysis undertaken in this paper is for an aerodynamically similar design with air as the working fluid. The rotational speed is 108,000 rpm and the overall static-to-total pressure ratio of 1.55. This paper concentrates on computational prediction of the performance of the compressor. The three-dimensional transient simulation is performed by using sliding mesh model (SMM). Blade tip leakage is not considered in the computation presented here. The unsteady solution predicts the interaction between IGV and the impeller, and between the impeller and the diffuser. The isentropic efficiency of impeller is found to be 81% at the design point. Based on the results obtained in this study, the inlet angle of diffuser vanes is modified to match the gas flow at the impeller exit, resulting in an increase of the isentropic efficiency of diffuser from 8.6% to 74.8%. It is also found that the performance of upstream components — IGV and impeller, are not affected by the performance of the diffuser.

Non-Axisymmetric End Wall Profiling in Transonic Compressors—Part I: Improving the Static Pressure Recovery at Off-Design Conditions by Sequential Hub and Shroud End Wall Profiling

2009 ◽  
Author(s):  
Steffen Reising ◽  
Heinz-Peter Schiffer
Keyword(s):  
Numerical Study ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Cross Flow ◽  
Axial Compressor ◽  
Secondary Flows ◽  
Flow Solver ◽  
Axial Compressors ◽  
Transonic Compressor ◽  
End Wall

Secondary flows involving cross flow and three-dimensional separation phenomena in modern axial compressors at high stage loading contribute significantly to a reduction in overall efficiency. This two-part paper presents a numerical study on the potential aerodynamic benefits of using non-axisymmetric end walls in an axial compressor, involving both the rotor and the stator row. This first paper describes the sequential profiling of stator end walls in a transonic compressor at several operating points to suppress separation. An automated multi-objective optimizer connected to a 3-D RANS flow solver was used to find the optimal end wall geometries. As a design exercise, the stator hub end wall of Configuration I of the Darmstadt Transonic Compressor was first optimized at design conditions, keeping the shroud end wall constant. This led to an increase in efficiency of 1.8% due to the suppression of the hub-corner stall. However, this was accompanied by an increased area of reverse flow at the casing, which was even more distinct at off-design conditions near stall. The numerical surge limit of the datum axisymmetric design could no longer be reached and was then determined by the new separation close to the stator casing. A subsequent optimization of the shroud end wall was carried out using the improved profiled hub as the initial design. An operating point near stall with a strongly developed separation was chosen for this purpose. The second optimization resulted in a further improvement in the characteristic speed line over the entire off-design region. Although the shroud contour was designed at off-design conditions, the optimization gained an additional 0.03% in efficiency for the design point. The lower surge limit of the datum design could also be reached again, even at higher efficiency and pressure ratios. The investigations showed that end wall profiling in high loaded compressor stators can be considered as a good supplement to 3-D blading to control separation areas and improve the entire component’s characteristics.

scholarly journals Research on the Influence of Axisymmetric Endwall on EAT Performance

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2215
Author(s):  
Han Teng ◽  
Wanyang Wu ◽  
Jingjun Zhong
Keyword(s):  
Total Pressure ◽  
Optimization Design ◽  
Pressure Ratio ◽  
Maximum Efficiency ◽  
Leakage Flow ◽  
Separation Flow ◽  
Suction Surface ◽  
Region Flow ◽  
Total Pressure Ratio ◽  
Isentropic Efficiency

To improve the performance of electrically assisted turbochargers (EATs), the influences of the hub profile and the casing profile on EAT performance were numerically studied by controlling the upper and lower endwall profiles. An artificial neural network and a genetic algorithm were used to optimize the endwall profile, considering the total pressure ratio and the isentropic efficiency at the peak efficiency point. Different performances of the prototype EAT and the optimized EAT under variable clearance sizes were discussed. The endwall profile affects an EAT by making the main flow structure in the endwall area decelerate and then accelerate due to the expansion and contraction of the meridional surface, which weakens the secondary leakage flow of the prototype EAT and changes the momentum ratio of the clearance leakage flow and the separation flow in the suction surface corner area. Because the tip region flow has a more significant influence on EAT performance, the optimal casing scheme has a better effect than the hub scheme. The optimization design can increase the isentropic efficiency of the maximum efficiency point by 1.5%, the total pressure ratio by 0.67%, the mass flow rate by 1.2%, and the general margin by 6.4%.

Time Resolved Simulation and Experimental Validation of the Flow in Axial Slot Casing Treatments for Transonic Axial Compressors

2008 ◽  
Author(s):  
Giovanni A. Brignole ◽  
Florian C. T. Danner ◽  
Hans-Peter Kau
Keyword(s):  
Mass Flow ◽  
Total Pressure ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Compressor Stage ◽  
Time Resolved ◽  
Transonic Compressor ◽  
Design Speed ◽  
Casing Treatments ◽  
Total Pressure Ratio

Building on the experience of previous investigations, a casing treatment was developed and applied to an axial transonic compressor stage, in literature referred to as Darmstadt Rotor 1. The aerodynamics of the experimental compressor stage was improved by applying axially orientated semicircular slots to the original plain casing, which both enhanced the operating range and design point efficiency. A gain in total pressure ratio along the entire design speed line was also observed. Within the scope of this study four different axial casing treatments were designed. Their effect on the flow in a transonic axial compressor stage was investigated parametrically using time-resolved 3D-FANS simulations with a mesh of approximately 4.8 · 106 grid points. This research aims to identify correlations between the geometrical cavity design and the changed channel flow. The findings help to formulate parameters for evaluating the performance of casing treatments. These criteria can further be used as target functions in the design optimisation process. The predicted behaviour of the transonic compressor was validated against experiments as well as an alternative numerical model, the non-linear harmonic method. Both confirmed the effect of the slots in raising efficiency as well as moving the design speed line towards higher pressure ratios. In the experiments, the addition of the slots increased the total pressure ratio at stall conditions by more than 5% and reduced mass flow from 87.5% of the design mass flow to less than 77.5% compared to the original geometry.

Non-Deterministic CFD Simulation of a Transonic Compressor Rotor

2009 ◽  
Author(s):  
Naveen Prasad Gopinathrao ◽  
David Bagshaw ◽  
Christophe Mabilat ◽  
Sohail Alizadeh
Keyword(s):  
Gas Turbine ◽  
Total Pressure ◽  
Polynomial Chaos ◽  
Cfd Simulation ◽  
Pressure Ratio ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Stochastic Methods ◽  
Transonic Compressor ◽  
Compressor Rotor

The compressor is one of the most sensitive components in a gas turbine. Small variations in geometry or operating conditions can have a detrimental effect on component performance, efficiency and life. During the past few years, significant effort has been invested in modelling the propagation of input uncertainties for CFD simulations using stochastic methods. Due to the large number of variables involved in typical industrial applications, problems often involve intensive computations, making the use of stochastic methods impractical. Therefore in addition to accuracy issues, the desire to reduce the computational overhead is also a key consideration in industrial applications. This work investigates the propagation of uncertainty within a transonic compressor rotor (NASA Rotor-37), using a Non Intrusive Polynomial Chaos methodology. Extensive computational research of this geometry has previously been undertaken and provides comparative data sets. The Non Intrusive Polynomial Chaos methodology is an inexpensive approach based on the spectral representation of the uncertainty parameters. The polynomial coefficients are evaluated using the Probabilistic Collocation method providing an exponential convergence for arbitrary probability distributions. Results will be shown for variations in inlet total pressure. The resulting performance parameters, including total pressure ratio and adiabatic efficiency, are presented along with their uncertainties. The paper serves as a description of the application of the Polynomial Chaos methodology, within a general purpose CFD software, to a gas turbine aerodynamics problem.

Research on Metamodel-Based Global Design Optimization and Data Mining Methods

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Liming Song ◽  
Zhendong Guo ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Data Mining ◽  
Performance Indicators ◽  
Total Pressure ◽  
Rotor Blade ◽  
Pressure Ratio ◽  
Optimal Solution ◽  
Parallel Axis ◽  
Transonic Rotor ◽  
Total Pressure Ratio ◽  
Isentropic Efficiency

The turbomachinery cascades design is a typical high dimensional computationally expensive and black box problem, thus a metamodel-based design optimization and data mining method is proposed and programed in this work, which is intended to gain knowledge of design space except for optimal solutions. The method combines a Kriging-based global algorithm with data mining techniques of self-organizing map (SOM), analysis of variance (ANOVA), and parallel axis. NACA Rotor 37, a typical axial transonic rotor blade, is selected for the research. Through SOM analysis, the overall changing trend of performance indicators like isentropic efficiency, total pressure ratio, and so on for the rotor blade is nearly consistent; therefore, a single-objective design for maximizing isentropic efficiency of the rotor blade with constraints prescribed on total pressure ratio and mass flow rate is carried out. The computational fluid dynamics (CFD) evaluations needed for the Kriging-based optimization process amount to only 1/5 of that required when employing a modified differential evolution (DE) algorithm as the optimizer. The isentropic efficiency of related optimal solution is 1.74% higher than the reference design. Then, the interactions among design variables and critical performance indicators as well as common features of better solutions are analyzed via ANOVA and parallel axis. Particularly, an ANOVA-based optimization is tried, which can validate the detected significant variables and gain knowledge of subspace with minimum cost. By integrating data mining results with practical knowledge of aerodynamics, it is confirmed that the shock wave has the most significant influence on the aerodynamic performance of transonic rotor blades. The sweep in tip section is found to be responsible for slight tradeoff relation between isentropic efficiency and total pressure ratio. The combinations of forward lean, thinner section profile near the blade leading edge, and compound sweep are favorable to get better aerodynamic performance, which is validated by the configuration of optimal solution obtained by MBGO algorithm.

Experimental and Numerical Analysis of Axial Skewed Slot Casing Treatments for a Transonic Compressor Stage

2009 ◽  
Author(s):  
Florian C. T. Danner ◽  
Hans-Peter Kau ◽  
Martin M. Mu¨ller ◽  
Heinz-Peter Schiffer ◽  
Giovanni A. Brignole
Keyword(s):  
Total Pressure ◽  
Pressure Ratio ◽  
Computational Domain ◽  
Compressor Stage ◽  
Time Resolved ◽  
Transonic Compressor ◽  
Computational Fluid Dynamics Analysis ◽  
Grid Points ◽  
Casing Treatments ◽  
Total Pressure Ratio

An investigation of a single-stage transonic compressor with axial skewed slot casing treatments is presented. The studied compressor stage is characterised by a design mass flow rate of 16 kg/s at a total pressure ratio of 1.5 and a rotor tip speed of 400m/s. The research comprises experimental measurements as well as time-resolved simulations at full and part speed. Total pressure ratio measurements and efficiency speedlines are complemented by traversing downstream of the stator and static pressure measurements at the rotor end wall. The experimental work is supported by unsteady computational fluid dynamics analysis to provide further insight into the ruling flow phenomena. The simulations were carried out fully three-dimensionally in a computational domain with approximately 4.8 million grid points including the cavity mesh. The application of the axial skewed slots led to both, an enhanced operating range and an increased design point efficiency. Rises in total pressure ratio along the entire speed lines were observed.

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