Unsteady Flow and Aeroelasticity Behavior of Aeroengine Core Compressors During Rotating Stall and Surge

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
M. Vahdati ◽  
G. Simpson ◽  
M. Imregun
Keyword(s):  
Experimental Data ◽  
Unsteady Flow ◽  
Mass Flow ◽  
Rotor Blade ◽  
Low Pressure ◽  
Rotating Stall ◽  
Flow Reversal ◽  
The Core ◽  
Single Passage ◽  
Operating Points

This paper will focus on two core-compressor instabilities, namely, rotating stall and surge. Using a 3D viscous time-accurate flow representation, the front bladerows of a core compressor were modeled in a whole-annulus fashion whereas the rest of bladerows were represented in single-passage fashion. The rotating stall behavior at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. Using a model with nine whole bladerows, the unsteady flow calculations were conducted on 32 CPUs of a parallel cluster, typical run times being around 3–4 weeks for a grid with about 60×106 points. The simulations were conducted over several engine rotations. As observed on the actual development engine, there was no rotating stall for the first scheduling condition while malscheduling of the stator vanes created a 12-band rotating stall which excited the rotor blade first flap mode. In a separate set of calculations, the surge behavior was modeled using a time-accurate single-passage representation of the core compressor. It was possible to predict not only flow reversal into the low pressure compression domain but also the expected hysteresis pattern of the surge loop in terms of its mass flow versus pressure characteristic.

Unsteady Flow and Aeroelasticity Behaviour of Aero-Engine Core Compressors During Rotating Stall and Surge

2006 ◽  
Author(s):  
M. Vahdati ◽  
G. Simpson ◽  
M. Imregun
Keyword(s):  
Experimental Data ◽  
Unsteady Flow ◽  
Mass Flow ◽  
Rotor Blade ◽  
Rotating Stall ◽  
Flow Reversal ◽  
The Core ◽  
Single Passage ◽  
Aero Engine ◽  
Operating Points

The paper will focus on two core-compressor instabilities, namely rotating stall and surge. Using a 3D viscous time-accurate flow representation, the front bladerows of a core-compressor were modelled in a whole-annulus fashion whereas the rest of bladerows were represented in single passage fashion. The rotating stall behaviour at two different compressor operating points was studied by considering two different variable-vane scheduling conditions for which experimental data were available. Using a model with 9 whole bladerows, the unsteady flow calculations were conducted on 32-CPUs of a parallel cluster, typical run times being around 3–4 weeks for a grid with about 60 million points. The simulations were conducted over several engine rotations. As observed on the actual development engine, there was no rotating stall for the first scheduling condition while mal-scheduling of the stator vanes created a 12 band rotating stall which excited the rotor blade 1st flap mode. In a separate set of calculations, the surge behaviour was modelled using a time-accurate single-passage representation of the core compressor. It was possible to predict not only flow reversal into the low pressure compression domain, but also the expected hysteresis pattern of the surge loop in terms of its mass flow vs pressure characteristic.

Unsteady Aerodynamics of Low-Pressure Steam Turbines Operating Under Low Volume Flow

2013 ◽  
Author(s):  
Benjamin Megerle ◽  
Timothy Stephen Rice ◽  
Ivan McBean ◽  
Peter Ott
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Measurement Data ◽  
Unsteady Aerodynamics ◽  
Low Pressure ◽  
Rotating Stall ◽  
Stage Model ◽  
Steam Turbines ◽  
Multi Stage ◽  
Low Volume

Non-synchronous excitation under low volume operation is a major risk to the mechanical integrity of last stage moving blades (LSMBs) in low-pressure (LP) steam turbines. These vibrations are often induced by a rotating aerodynamic instability similar to rotating stall in compressors. Currently extensive validation of new blade designs is required to clarify whether they are subjected to the risk of not admissible blade vibration. Such tests are usually performed at the end of a blade development project. If resonance occurs a costly redesign is required, which may also lead to a reduction of performance. It is therefore of great interest to be able to predict correctly the unsteady flow phenomena and their effects. Detailed unsteady pressure measurements have been performed in a single stage model steam turbine operated with air under ventilation conditions. 3D CFD has been applied to simulate the unsteady flow in the air model turbine. It has been shown that the simulation reproduces well the characteristics of the phenomena observed in the tests. This methodology has been transferred to more realistic steam turbine multi stage environment. The numerical results have been validated with measurement data from a multi stage model LP steam turbine operated with steam. Measurement and numerical simulation show agreement with respect to the global flow field, the number of stall cells and the intensity of the rotating excitation mechanism. Furthermore, the air model turbine and model steam turbine numerical and measurement results are compared. It is demonstrated that the air model turbine is a suitable vehicle to investigate the unsteady effects found in a steam turbine.

scholarly journals Consistent Posttest Calculations for LOCA Scenarios in LOBI Integral Facility

2012 ◽  
Vol 2012 ◽  
pp. 1-16 ◽  
Author(s):  
F. Reventós ◽  
P. Pla ◽  
C. Matteoli ◽  
G. Nacci ◽  
M. Cherubini ◽  
...  
Keyword(s):  
Experimental Data ◽  
Mass Flow ◽  
Scaling Factor ◽  
Test Facility ◽  
Data Bases ◽  
Integral Test ◽  
The Core ◽  
Active Elements ◽  
Accuracy Data

Integral test facilities (ITFs) are one of the main tools for the validation of best estimate thermalhydraulic system codes. The experimental data are also of great value when compared to the experiment-scaled conditions in a full NPP. The LOBI was a single plus a triple-loop (simulated by one loop) test facility electrically heated to simulate a 1300 MWe PWR. The scaling factor was 712 for the core power, volume, and mass flow. Primary and secondary sides contained all main active elements. Tests were performed for the characterization of phenomenologies relevant to large and small break LOCAs and special transients in PWRs. The paper presents the results of three posttest calculations of LOBI experiments. The selected experiments are BL-30, BL-44, and A1-84. They are LOCA scenarios of different break sizes and with different availability of safety injection components. The goal of the analysis is to improve the knowledge of the phenomena occurred in the facility in order to use it in further studies related to qualifying nodalizations of actual plants or to establish accuracy data bases for uncertainty methodologies. An example of procedure of implementing changes in a common nodalization valid for simulating tests occurred in a specific ITF is presented along with its confirmation based on posttests results.

Geometric considerations in the capture of localized flow reversal in centrifugal compressor vaneless diffusers using steady state simulations

2016 ◽  
Vol 231 (21) ◽  
pp. 3959-3973
Author(s):  
Chris Clarke ◽  
Russell Marechale ◽  
Abraham Engeda ◽  
Michael Cave
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Centrifugal Compressor ◽  
Flow Characteristics ◽  
Rotating Stall ◽  
Flow Reversal ◽  
Contour Plot ◽  
Vaneless Diffuser ◽  
Impeller Blade ◽  
Steady State Simulation

A steady state simulation procedure is proposed to capture localized flow reversal inside of a centrifugal compressor vaneless diffuser. The procedure was performed on 12 compressor stages of varying geometry for speed lines of 13,100, 19,240, and 21,870 r/min. The simulations were run for all points from choke to surge including the experimentally determined rotating stall onset point. The experimental data and geometry were provided by Solar Turbines Inc. San Diego, CA. It was found possible to capture localized flow reversal inside of a vaneless diffuser using a steady state simulation. The results showed that using a geometric parameter, comparing the diffuser width, b4, to the impeller blade pitch distance, dpitch, it could be determined whether or not a steady state simulation could capture localized flow reversal. For values of b4/dpitch beneath 0.152 flow reversal could not be captured. But, for values of b4/dpitch above 0.177 localized flow reversal was captured. For values between 0.152 and 0.177, no conclusions could be drawn. Where possible, experimental data were compared against the diffuser inlet and outlet numerical profiles and the meridional contour plot. These comparisons served to validate the approach used in this article. These validations showed that the procedure defined herein is accurate and trustworthy within a specific range of geometric and flow characteristics. There are two other conclusions. First, the b4/dpitch parameter helps to define the type of flow breakdown. For b4/dpitch below 0.152, the flow breaks down in the circumferential direction, but for values of b4/dpitch above 0.177, the flow breaks down in the span-wise direction. Second, the simulations were able to capture instances of localized flow reversal before rotating stall onset. This concludes that localized flow reversal is not the determining factor in rotating stall onset as has been suggested by other investigators.

Unsteady Flow Effect on Nonequilibrium Condensation in 3-D Low Pressure Steam Turbine Stages

2013 ◽  
Author(s):  
Satoshi Miyake ◽  
Satoru Yamamoto ◽  
Yasuhiro Sasao ◽  
Kazuhiro Momma ◽  
Toshihiro Miyawaki ◽  
...  
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Cross Sections ◽  
Rotor Blade ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Low Pressure ◽  
Multi Stage ◽  
Pressure Steam ◽  
Nonequilibrium Condensation

A numerical study simulating unsteady 3-D wet-steam flows through three-stage stator-rotor blade rows in a low-pressure steam turbine model experimentally conducted by Mitsubishi Heavy Industry (MHI) was presented in the last ASME Turbo Expo by our group. In this study, the previous discussion is extended to the discussion how nonequilibrium condensation is influenced by unsteady wakes and corner vortices from prefaced multi-stage blade rows. Unsteady 3-D flows through three-stage stator-rotor blade rows are simulated assuming nonequilibrium condensation. Flows with a different inlet flow condition are calculated and the results are compared with each other. Instantaneous condensate mass fractions are visualized at different spans and cross sections in the three-stage stator and rotor blade rows. Also the time and space dependent values are plotted and the obtained unsteady flow characteristics are explained.

An Enhanced Off-Design Performance Model for Single Stage Fans

2014 ◽  
Author(s):  
Joachim Kurzke
Keyword(s):  
Flow Field ◽  
Mass Flow ◽  
Rotor Blade ◽  
Total Mass ◽  
Pressure Ratio ◽  
Fan Performance ◽  
The Core ◽  
Velocity Triangle ◽  
Tip Radius ◽  
Bypass Ratio

Modern high bypass turbofan engines have single stage fans with a low hub-tip radius ratio. The fan map is a very important element for off-design performance simulations. Such a map consists of tables with corrected mass flow, pressure ratio and efficiency for a range of corrected spool speeds. Applying the data read from a fan map to both the core and the bypass stream is inaccurate because the transonic flow field of the bypass stream is very different to the subsonic flow field of the core stream. A better approximation of reality is to use a hybrid map with total mass flow, bypass pressure ratio and efficiency. Constant factors are employed to derive the core stream pressure ratio and efficiency. For more accurate simulations two maps may be employed, one for the core and another one for the bypass stream. The total mass flow of the fan is the same in these two maps while pressure ratio and efficiency are different for the two streams. The data for each point in this so-called “Split Map” are valid for a pre-defined bypass ratio. This paper describes an alternative to the split map methodology which takes the variability of the bypass ratio into account in a different way. The hypothesis is that the overall fan performance is not affected by variations in bypass ratio. The fan performance map is completed by an additional table with core stream efficiency. This enhanced map is used as follows. When scaling the map, the bypass ratio as well as the pressure ratio and efficiencies for the core and bypass streams are known. Assumed values for fan tip speed, hub-tip radius ratio and fan inlet Mach number yield the core stream velocity triangle. The rotor blade exit flow angle from this triangle remains the same in all other operating conditions. The core flow velocity triangle analysis with known rotor blade exit angle yields the work done on the core stream during off-design. The pressure ratio is calculated from this work and the efficiency read from the core stream efficiency table mentioned above. Finally, the bypass stream pressure ratio and efficiency are calculated from the overall map and the core stream data applying the actual bypass ratio.

scholarly journals Experimental Investigation of Steady and Unsteady Flow Field Downstream of an Automotive Torque Converter Turbine and Stator

1995 ◽  
Vol 2 (2) ◽  
pp. 67-84 ◽  
Author(s):  
B. V. Marathe ◽  
B. Lakshminarayana
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Unsteady Flow ◽  
Torque Converter ◽  
Mean Value ◽  
Frame Of Reference ◽  
Secondary Flows ◽  
Flow Properties ◽  
The Core ◽  
Stationary Frame

The objective of this investigation is to understand the steady and the unsteady flow field at the exit of an automotive torque converter turbine and stator with a view towards improving it's performance. A high frequency response five-hole probe was designed and built to measure the three-dimensional steady and unsteady flow fields. The measurements were conducted in a stationary frame of reference and the data were processed to derive the flow properties in the relative (turbine) frame of reference. The experimental data were processed in the frequency domain by spectrum analysis and in temporal-spatial domain by ensemble averaging technique. The data show that the flow field is highly unsteady with high unresolved unsteadiness (approx. 17-21% of mean value) and significant blade-to-blade periodic component approx. 6% of mean value). The unresolved unsteadiness and periodic unsteadiness increase with an increase in the radius from the shell to the core whereas the aperiodic unsteadiness does not show any systematic variation with the radius. The experimental data reveal the presence of a low momentum region near the core due to possible flow separation and reattachment inside the turbine passage. Data also show the presence of strong secondary flow near the core and weak secondary flow near the shell at the exit of the turbine. These secondary flows generate high levels of turbulence. A comparison of the flow properties upstream and downstream of the stator in the stationary frame of reference indicate the presence of high losses near the core due to high turbulence levels and large secondary flows, and high losses near the shell due to possible corner separation near the shell suction surface inside the stator blade passage. The unsteadiness in the flow properties upstream of the stator is high. The rms value of the unsteady total velocity is approx. 20% of the steady state value. Periodic and aperiodic unsteadiness were also found significant.

Prediction of Unsteady Rotor-Surface Pressure and Heat Transfer From Wake Passings

1992 ◽  
Vol 114 (4) ◽  
pp. 807-817 ◽  
Author(s):  
L. T. Tran ◽  
D. B. Taulbee
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Heat Flux ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Numerical Solutions ◽  
Inviscid Flow ◽  
Blade Surface ◽  
Blade Passage

The research described in this paper is a numerical investigation of the effects of unsteady flow on gas turbine heat transfer, particularly on a rotor blade surface. The unsteady flow in a rotor blade passage and the unsteady heat transfer on the blade surface as a result of wake/blade interaction are modeled by the inviscid flow/boundary layer approach. The Euler equations that govern the inviscid flow are solved using a time-accurate marching scheme. The unsteady flow in the blade passage is induced by periodically moving a wake model across the passage inlet. Unsteady flow solutions in the passage provide pressure gradients and boundary conditions for the boundary-layer equations that govern the viscous flow adjacent to the blade surface. Numerical solutions of the unsteady turbulent boundary layer yield surface heat flux values that can then be compared to experimental data. Comparisons with experimental data show that unsteady heat flux on the blade suction surface is well predicted, but the predictions of unsteady heat flux on the blade pressure surface do not agree.

A Dangerous Blade Vibration Phenomenon due to Unsteady Flow in Centrifugal Compressors

1993 ◽  
Author(s):  
D. Jin ◽  
H. Hasemann ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Unsteady Flow ◽  
Mass Flow ◽  
Reverse Flow ◽  
Broad Band ◽  
Rotating Stall ◽  
High Mass ◽  
Resonance Excitation ◽  
Blade Vibration ◽  
Unsteady Pressure ◽  
Vane Diffuser

Dangerous blade excitation caused by unsteady flow in a high pressure/high mass flow compressor running in a low mass flow region has been investigated. Experiments were carried out for compressors with two different types of vaned diffusers. Blade vibration was measured with strain gages while simultaneous unsteady pressure was measured with fast response dynamic transducers. All measured results were analysed in detail so that an in-depth understanding of blade excitation mechanism can be obtained. Firstly, the compressor with a straight-channel vane diffuser at reduced rotational speed of 12,300 rpm in an unstable operation region was considered. The analysis of blade vibration and unsteady pressure showed an unusual excitation phenomenon. Besides a strong blade vibration frequency component near the first blade mode frequency excited by the rotating stall cells existed another dangerous resonance excitation with first blade mode component which dominated the blade vibration spectrum. A detailed pressure signal analysis indicated that this blade vibration was excited by a broad band pressure fluctuation due to a strong reverse flow occurring simultaneously with the rotating stall. Further reducing the compressor mass flow to the operation point shortly before surge, the rotating stall was significantly weakened while the reverse flow kept its intensity until surge occurred. In this operation region blades suffered throughout a violent excitation of resonance because of the strong reverse flow. These blade excitation phenomena were also found in the next experiment for the compressor with a cambered vane diffuser at higher rotational speeds of nred = 13,500 and 14,000 rpm. The maximum strain values of blade vibration were obtained to quantitavely estimate the danger of blade vibration caused by this excitation.

Unsteady Aerodynamics of Low-Pressure Steam Turbines Operating Under Low Volume Flow

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Benjamin Megerle ◽  
Ivan McBean ◽  
Timothy Stephen Rice ◽  
Peter Ott
Keyword(s):  
Unsteady Flow ◽  
Steam Turbine ◽  
Measurement Data ◽  
Unsteady Aerodynamics ◽  
Low Pressure ◽  
Development Project ◽  
Rotating Stall ◽  
Steam Turbines ◽  
Blade Vibration ◽  
Low Volume

Nonsynchronous excitation under low volume operation is a major risk to the mechanical integrity of last stage moving blades (LSMBs) in low-pressure (LP) steam turbines. These vibrations are often induced by a rotating aerodynamic instability similar to rotating stall in compressors. Currently extensive validation of new blade designs is required to clarify whether they are subjected to the risk of not admissible blade vibration. Such tests are usually performed at the end of a blade development project. If resonance occurs a costly redesign is required, which may also lead to a reduction of performance. It is therefore of great interest to be able to predict correctly the unsteady flow phenomena and their effects. Detailed unsteady pressure measurements have been performed in a single stage model steam turbine operated with air under ventilation conditions. 3D computational fluid dynamics (CFD) has been applied to simulate the unsteady flow in the air model turbine. It has been shown that the simulation reproduces well the characteristics of the phenomena observed in the tests. This methodology has been transferred to more realistic steam turbine multistage environment. The numerical results have been validated with measurement data from a multistage model LP steam turbine operated with steam. Measurement and numerical simulation show agreement with respect to the global flow field, the number of stall cells and the intensity of the rotating excitation mechanism. Furthermore, the air model turbine and model steam turbine numerical and measurement results are compared. It is demonstrated that the air model turbine is a suitable vehicle to investigate the unsteady effects found in a steam turbine.

Sign in / Sign up

Export Citation Format

Share Document