Numerical Evaluation of Losses in Shrouded and Cantilevered Stators of a Multi-Stage Axial Compressor

2021 ◽  
Author(s):  
Ilaria De Dominicis ◽  
Sebastian Robens ◽  
Volker Gümmer
Keyword(s):  
Numerical Evaluation ◽  
Axial Compressor ◽  
Entropy Change ◽  
Stagnation Pressure ◽  
Loss Coefficient ◽  
Stagnation Temperature ◽  
Axial Compressors ◽  
Multi Stage ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

Abstract The loss coefficient based only on the stagnation pressure has traditionally been used in the analysis of axial compressors for the comparison between shrouded and cantilevered stator configurations. In recent years, engineers have been able to perform more detailed Computational Fluid Dynamics simulations, allowing them to resolve the flow field in the leakage paths. The two stator hub designs are, however, affected by the rotating surfaces in a different way: in cantilevered stators, the relative rotation between the stator and the hub imparts energy to the hub flow, whereas in shrouded stators, the rotating inner leakage surface imparts energy to the seal cavity leakage flow. The aim of this work is to analyze the performance of a multi-stage axial compressor featuring a change of stator hub configuration, by employing both the conventional loss coefficient based on the stagnation pressure and the loss coefficient based on the entropy change. It is shown, that in the evaluation of the losses of a multi-stage axial machine, it is essential to consider the different 3D distributions of stagnation temperature resulting from the two stator hub configurations, which are transferred to the downstream rows.

Reducing Instrumentation Errors Caused by Circumferential Flow-Field Variations in Multistage Axial Compressors

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
M. Chilla ◽  
G. Pullan ◽  
S. Gallimore
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Sampling Error ◽  
Leading Edge ◽  
Stagnation Pressure ◽  
Wave Number ◽  
Stagnation Temperature ◽  
Sampling Errors ◽  
Mean Flow ◽  
Axial Compressors

Abstract The effects of blade row interactions on stator-mounted instrumentation in axial compressors are investigated using unsteady numerical calculations. The test compressor is an eight-stage machine representative of an aero-engine core compressor. For the unsteady calculations, a 180-deg sector (half-annulus) model of the compressor is used. It is shown that the time-mean flow field in the stator leading edge planes is circumferentially nonuniform. The circumferential variations in stagnation pressure and stagnation temperature, respectively, reach 4.2% and 1.1% of the local mean. Using spatial wave number analysis, the incoming wakes from the upstream stator rows are identified as the dominant source of the circumferential variations in the front and middle of the compressor, while toward the rear of the compressor, the upstream influence of the eight struts in the exit duct becomes dominant. Based on three circumferential probes, the sampling errors for stagnation pressure and stagnation temperature are calculated as a function of the probe locations. Optimization of the probe locations shows that the sampling error can be reduced by up to 77% by circumferentially redistributing the individual probes. The reductions in the sampling errors translate to reductions in the uncertainties of the overall compressor efficiency and inlet flow capacity by up to 50%. Recognizing that data from large-scale unsteady calculations are rarely available in the instrumentation phase for a new test rig or engine, a method for approximating the circumferential variations with single harmonics is presented. The construction of the harmonics is based solely on the knowledge of the number of stators in each row and a small number of equispaced probes. It is shown how excursions in the sampling error are reduced by increasing the number of circumferential probes.

scholarly journals Computational fluid dynamics simulations of blade damage effect on the performance of a transonic axial compressor near stall

2014 ◽  
Vol 229 (12) ◽  
pp. 2242-2260 ◽  
Author(s):  
Yan-Ling Li ◽  
Abdulnaser I Sayma
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Damage Effect ◽  
Computational Fluid Dynamics Simulations ◽  
Compressor Performance ◽  
Transonic Axial Compressor ◽  
Dynamics Simulations ◽  
Rotor Assembly

Gas turbine axial compressor blades may encounter damage during service for various reasons such as damage by debris from casing or foreign objects impacting the blades, typically near the rotor’s tip. This may lead to deterioration of performance and reduction in the surge margin. The damage breaks the cyclic symmetry of the rotor assembly; thus, computational fluid dynamics simulations have to be performed using full annulus compressor assembly. Moreover, downstream boundary conditions are unknown during rotating stall or surge, and simulations become difficult. This paper presents unsteady computational fluid dynamics analyses of compressor performance with tip curl damage. Computations were performed near the stall boundary. The primary objectives are to understand the effect of the damage on the flow behaviour and compressor stability. Computations for the undamaged rotor assembly were also performed as a reference case. A transonic axial compressor rotor was used for the time-accurate numerical unsteady flow simulations, with a variable area nozzle downstream simulating an experimental throttle. Computations were performed at 60% of the rotor design speed. Two different degrees of damage for one blade and multiple damaged blades were investigated. Rotating stall characteristics differ including the number of stall cells, propagation speed and rotating stall cell characteristics. Contrary to expectations, damaged blades with typical degrees of damage do not show noticeable effects on the global compressor performance near stall.

Investigations on Impulse Blade Cascades with Medium Deflection

1978 ◽  
Vol 100 (3) ◽  
pp. 432-438
Author(s):  
K. Bammert ◽  
B. Ahmadi
Keyword(s):  
Wind Tunnel ◽  
Axial Compressor ◽  
Two Dimensional ◽  
Axial Compressors ◽  
High Reaction ◽  
Multi Stage ◽  
Tandem Cascades

The transformation of energy in the stages of high-reaction axial compressors can be considerably increased if the rotor blading consists of tandem cascades. This also involves aerodynamically higher loading of the stator cascades deflecting the flow. The behavior of the base, mean, and tip sections impulse cascades of the stator of a multi-stage axial compressor designed on this basis was examined in a two-dimensional cascade wind tunnel. The results of these investigations are reported and discussed.

Study of Tip Flows in High Hub-to-Tip Ratio Axial Compressors at Low Speed With Varying Tip Gaps, Inflow Conditions and Tip Shapes

2010 ◽  
Author(s):  
Bhaskar Roy ◽  
A. M. Pradeep ◽  
A. Suzith ◽  
Dinesh Bhatia ◽  
Aditya Mulmule
Keyword(s):  
Axial Compressor ◽  
Tip Vortex ◽  
Low Flow ◽  
Tip Leakage Flow ◽  
Design Point ◽  
Axial Compressors ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Multi Stage ◽  
Performance Deterioration

The present study involves simulation of a single compressor rotor with a high hub-to-tip ratio blade. The study includes the effect of variation of tip gap, of tip shapes and of inlet axial velocity profiles, with inflows simulated similar to that of a typical rear stage environment of a multi-stage axial compressor. Numerical studies were carried out on a baseline rotor blade (without sweep or dihedral) and then on blades with sweep and dihedral applied at the tip region of the rotor. Simulation of these part-span sweep and dihedral shapes are done to study their effects on blade tip leakage flow. Results show that sweep and dihedral, in some cases, produce favorable tip flows, improving blade aerodynamics. Positive dihedral caused weakening of tip leakage vortex at design point as well as at peak pressure point. Negative dihedral may help postpone stall at the high pressure, low flow operation. Backward sweep weakened tip vortex at the design point. Contrary to some of the studies reported earlier forward sweep, when applied at the tip region, showed performance deterioration over the most of the operating range of the high hub-to-tip rotor.

Viscous Throughflow Modelling for Multi-Stage Compressor Design

1992 ◽  
Author(s):  
M. A. Howard ◽  
S. J. Gallimore
Keyword(s):  
Shear Force ◽  
High Speed ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Design System ◽  
Flow Angle ◽  
Axial Compressors ◽  
Multi Stage ◽  
Viscous Shear ◽  
Compressor Design

An existing throughflow method for axial compressors, which accounts for the effects of spanwise mixing using a turbulent diffusion model, has been extended to include the viscous shear force on the endwall. The use of a shear force, consistent with a no-slip condition, on the annulus walls in the throughflow calculations allows realistic predictions of the velocity and flow angle profiles near the endwalls. The annulus wall boundary layers are therefore incorporated directly in the throughflow prediction. This eliminates the need for empirical blockage factors or independent annulus boundary layer calculations. The axisymmetric prediction can be further refined by specifying realistic spanwise variations of loss coefficient and deviation to model the three-dimensional endwall effects. The resulting throughflow calculation gives realistic predictions of flow properties across the whole span of a compressor. This is confirmed by comparison with measured data from both low and high speed multi-stage machines. The viscous throughflow method has been incorporated into an axial compressor design system. The method predicts the meridional velocity defects in the endwall region and consequently blading can be designed which allows for the increased incidence, and low dynamic head, near to the annulus walls.

scholarly journals Physics of Airfoil Clocking in a High-Speed Axial Compressor

1998 ◽  
Author(s):  
Daniel J. Dorney ◽  
Om P. Sharma ◽  
Karen L. Gundy-Burlet
Keyword(s):  
Relative Motion ◽  
High Speed ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Unsteady Aerodynamics ◽  
Navier Stokes ◽  
Jet Engines ◽  
Axial Compressors ◽  
Multi Stage ◽  
Significant Performance

Axial compressors have inherently unsteady flow fields because of relative motion between rotor and stator airfoils. This relative motion leads to viscous and inviscid (potential) interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of convected wakes can lead to progressively more complex wake/wake and wake/airfoil interactions. Variations in the relative circumferential positions of stators or rotors can change these interactions, leading to different unsteady forcing functions on airfoils and different compressor efficiencies. In addition, as the Mach number increases the interaction between blade rows can be intensified due to potential effects. In the current study an unsteady, quasi-three-dimensional Navier-Stokes analysis has been used to investigate the unsteady aerodynamics of stator clocking in a 1-1/2 stage compressor, typical of back stages used in high-pressure compressors of advanced commercial jet engines. The effects of turbulence have been modeled with both algebraic and two-equation models. The results presented include steady and unsteady surface pressures, efficiencies, boundary layer quantities and turbulence quantities. The main contribution of the current work has been to show that airfoil clocking can produce significant performance variations at the Mach numbers associated with an engine operating environment. In addition, the growth of turbulence has been quantified to aid in the development of models for the multi-stage steady analyses used in design systems.

scholarly journals Analytical model for the power-yaw sensitivity of wind turbines operating in full wake

2019 ◽  
Author(s):  
Jaime Liew ◽  
Albert M. Urbán ◽  
Søren Juhl Andersen
Keyword(s):  
Wind Turbines ◽  
Wind Field ◽  
Wind Farm ◽  
Power Production ◽  
Loss Coefficient ◽  
Wake Flow ◽  
Wind Farm Optimization ◽  
Wake Effects ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

Abstract. Wind turbines are designed to align themselves with the incoming wind direction. However, turbines often experience unintentional yaw misalignment, which can significantly reduce the power production. The unintentional yaw misalignment increase for turbines operating in wake of upstream turbines. Here, the combined effects of wakes and yaw misalignment are investigated with the resulting reduction in power production. A model is developed, which considers the trajectory of each turbine blade element as it passes through the waked wind field in order to determine a power-yaw loss coefficient. The simple model is verified using the HAWC2 aeroelastic code, where wake flow fields have been generated using both medium and high-fidelity computational fluid dynamics simulations. It is demonstrated that the spatial variation of the incoming wind field, due to the presence of wake(s), plays a significant role in the power loss due to yaw misalignment. Results show that disregarding these effects on the power-yaw loss coefficient can yield a 3.5 % overestimation in the power production of a turbine misaligned by 30°. The presented analysis and model is relevant to low-fidelity wind farm optimization tools, which aim to capture the effects of wake effects and yaw misalignment as well as uncertainty on power output.

scholarly journals Design optimization of a multi-stage axial compressor using throughflow and a database of optimal airfoils

2018 ◽  
Vol 2 ◽  
pp. W5N91I ◽  
Author(s):  
Markus Schnoes ◽  
Christian Voß ◽  
Eberhard Nicke
Keyword(s):  
Axial Compressor ◽  
Axial Compressors ◽  
New Class ◽  
Multi Stage ◽  
Blade Row ◽  
Wall Flow ◽  
Tool Set ◽  
And Performance ◽  
Gas Turbine Compressor ◽  
End Wall

The basic tool set to design multi-stage axial compressors consists of fast codes for throughflow and blade-to-blade analysis. Detailed blade row design is conducted with 3D CFD, mainly to control the end wall flow. This work focuses on the interaction between throughflow and blade-to-blade design and the transition to 3D CFD. A design strategy is presented that is based on a versatile airfoil family. The new class of airfoils is generated by optimizing a large number of airfoil shapes for varying design requirements. Each airfoil geometry satisfies the need for a wide working range as well as low losses. Based on this data, machine learning is applied to estimate optimal airfoil shape and performance. The performance prediction is incorporated into the throughflow code. Based on a throughflow design, the airfoils can be stacked automatically to generate 3D blades. On this basis, a 3D CFD setup can be derived. This strategy is applied to study upgrade options for a 15-stage stationary gas turbine compressor test rig. At first, the behavior of the new airfoils is studied in detail. Afterwards, the design is optimized for mass flow rate as well as efficiency. Selected configurations from the Pareto-front are evaluated with 3D CFD.

Reducing Instrumentation Errors Caused by Circumferential Flow Field Variations in Multi-Stage Axial Compressors

2019 ◽  
Author(s):  
M. Chilla ◽  
G. Pullan ◽  
S. Gallimore
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Sampling Error ◽  
Leading Edge ◽  
Stagnation Pressure ◽  
Wave Number ◽  
Stagnation Temperature ◽  
Sampling Errors ◽  
Mean Flow ◽  
Axial Compressors

Abstract The effects of blade row interactions on stator-mounted instrumentation in axial compressors are investigated using unsteady numerical calculations. The test compressor is an 8-stage machine representative of an aero-engine core compressor. For the unsteady calculations, a 180deg sector (half-annulus) model of the compressor is used. It is shown that the time-mean flow field in the stator leading edge planes is circumferentially non-uniform. The circumferential variations in stagnation pressure and stagnation temperature respectively reach 4.2% and 1.1% of the local mean. Using spatial wave number analysis, the incoming wakes from the upstream stator rows are identified as the dominant source of the circumferential variations in the front and middle of the compressor, while towards the rear of the compressor, the upstream influence of the eight struts in the exit duct becomes dominant. Based on three circumferential probes, the sampling errors for stagnation pressure and stagnation temperature are calculated as a function of the probe locations. Optimization of the probe locations shows that the sampling error can be reduced by up to 77% by circumferentially redistributing the individual probes. The reductions in the sampling errors translate to reductions in the uncertainties of the overall compressor efficiency and inlet flow capacity by up to 50%. Recognizing that data from large-scale unsteady calculations is rarely available in the instrumentation phase for a new test rig or engine, a method for approximating the circumferential variations with single harmonics is presented. The construction of the harmonics is based solely on the knowledge of the number of stators in each row and a small number of equi-spaced probes. It is shown how excursions in the sampling error are reduced by increasing the number of circumferential probes.

Optimization of the Workflow of Multistage Axial Compressors Using Modern Gas Dynamics Computing Systems

2020 ◽  
Author(s):  
Grigorii Popov ◽  
Evgenii Goriachkin ◽  
Oleg Baturin ◽  
Valerii Matveev ◽  
Igor Egorov ◽  
...  
Keyword(s):  
Gas Dynamics ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Calculation Model ◽  
Cfd Modeling ◽  
Compressor Blades ◽  
Stability Margins ◽  
Axial Compressors ◽  
Cfd Models ◽  
Multi Stage

Abstract Current developmental level of computers and numerical methods of gas dynamics makes it possible to optimize compressors using 3D CFD models. Design variants for the compressor can be automatically generated that best suit all the design requirements and limitations. However, the methods and tool for optimizing compressors are not sufficiently developed for the successful application. The problems lie in the large size of the calculation model, the solution time and the requirements for computer resources. In present study, a method for finding the optimal configuration of the blades of multi-stage axial compressors using 3D CFD modeling and commercial optimization programs as the main tools was developed. The basic parameters of the compressor (efficiency, pressure ratio, mass flow rate, etc.) can be improved using the created method correcting the shape of the blade profiles and their relative position. The method considers presence of various constraints. When developing the method, special attention was paid to the creation of an algorithm for parameterizing the blade shape and a program based on it, which can automatically change the shape of the axial compressor blades. They were used by the authors during optimization as a tool that converts variable parameters into the “new” blade geometry. Recommendations were also found on the rational settings for the CFD models used in the optimization of axial compressors. The paper provides a brief overview of several works related to the optimization of multi-stage gas turbine axial compressors for various purposes (number of stages from 3 to 15), successfully performed using the developed method. As a result, an increase was achieved in efficiency, pressure ratio and stability margins.

Sign in / Sign up

Export Citation Format

Share Document