The Impact of Rotor Inlet Cavity Volume and Length Scale on Efficiency

2012 ◽  
Author(s):  
Konstantinos G. Barmpalias ◽  
Reza S. Abhari ◽  
Anestis I. Kalfas ◽  
Naoki Shibukawa ◽  
Takashi Sasaki
Keyword(s):  
Experimental Work ◽  
Computational Analysis ◽  
Cavity Length ◽  
Cavity Wall ◽  
Length Scale ◽  
Cavity Volume ◽  
Turbine Stage ◽  
Flow Interactions ◽  
The Impact ◽  
Stage Efficiency

The interaction between the cavity and the main flows accounts for a considerable amount of the overall aerodynamic losses in axial turbomachinery. Experimental work supplemented by a computational analysis is presented in this paper on the impact of rotor inlet cavity volume and length scale on turbine stage efficiency. Inlet cavity volume and geometry have been systematically varied. The flow interactions occurring at the cavity inlet between the cavity and main flows and their subsequent impact on efficiency were studied. Five different configurations have been examined within this study. The radial cavity wall has been shortened by 13% and 25% compared to the initial cavity length. Cavity volume has been reduced by 14% and 28% respectively. An additional rounding introduced at the upper right corner of the cavity generated two more variations. Efficiency was increased by 1.1% and 1.6% for the 14% and 28% cavity volume reductions, respectively. The rounding introduced led only to efficiency deficits as the strengthening of the cavity vortex caused increased interaction at the cavity inlet area.

Experimental Investigation of Purge Flow Effects on a High Pressure Turbine Stage

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
K. Regina ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Experimental Investigation ◽  
High Pressure ◽  
Gas Turbines ◽  
Radial Displacement ◽  
Secondary Flows ◽  
Turbine Stage ◽  
Flow Factor ◽  
Purge Flow ◽  
The Impact ◽  
Stage Efficiency

In the present paper, an experimental investigation of the effects of rim seal purge flow on the performance of a highly loaded axial turbine stage is presented. The test configuration consists of a one-and-a-half stage, unshrouded, turbine, with a blading representative of high pressure (HP) gas turbines. Efficiency measurements for various purge flow injection levels have been carried out with pneumatic probes at the exit of the rotor and show a reduction of isentropic total-to-total efficiency of 0.8% per percent of injected mass flow. For three purge flow conditions, the unsteady aerodynamic flow field at rotor inlet and rotor exit has been measured with the in-house developed fast response aerodynamic probe (FRAP). The time-resolved data show the unsteady interaction of the purge flow with the secondary flows of the main flow and the impact on the radial displacement of the rotor hub passage vortex (HPV). Steady measurements at off-design conditions show the impact of the rotor incidence and of the stage flow factor on the resulting stage efficiency and the radial displacement of the rotor HPV. A comparison of the effect of purge flow and of the off-design conditions on the rotor incidence and stage flow factor shows that the detrimental effect of the purge flow on the stage efficiency caused by the radial displacement of the rotor HPV is dominated by the increase of stage flow factor in the hub region rather than by the increase of negative rotor incidence.

Design Considerations for Axial Steam Turbine Rotor Inlet Cavity Volume and Length Scale

2011 ◽  
Author(s):  
Konstantinos G. Barmpalias ◽  
Anestis I. Kalfas ◽  
Reza S. Abhari ◽  
Toshio Hirano ◽  
Naoki Shibukawa ◽  
...  
Keyword(s):  
Computational Analysis ◽  
Turbine Rotor ◽  
Volume Reduction ◽  
Length Scale ◽  
Toroidal Vortex ◽  
Cavity Volume ◽  
Design Considerations ◽  
Baseline Case ◽  
Design Perspective ◽  
Reduction Case

In this paper we examine the interaction between the cavity and main flows of three different rotor cavities. For each of the three rotor cavities, the cavity inlets differ in their axial cavity lengths, which are modified by extending the upper casing stator platform. The three cavity volumes are comprised of a baseline case, along with a 14% and a 28% volume reduction relative to the baseline case. Measurements show that there is an increase in efficiency of 0.3% for the 14% cavity volume reduction case (relative to the baseline case), whereas a further volume reduction of 28% (relative to the baseline case) decreases the efficiency. Computational analysis highlights the break-up of a toroidal vortex within the cavity as the primary factor explaining the changes in efficiency. The dominant cavity vortex originally present in the baseline case firstly broken up into two smaller vortices for the 14% cavity volume reduction case and secondly, completely replaced with a strong radial jet for the 28% volume reduction case. From a design perspective, reducing the cavity volume by extending the upper casing stator platform yields improvements in efficiency provided that the cavity vortex is still present. The design considerations, analysis and the associated aerodynamics are discussed in detail within this paper.

Studies on the Impact of Choice of Gas Models in an Un-Cooled Turbine Stage

2014 ◽  
Author(s):  
Karthik Srinivasan ◽  
David Newman ◽  
Abhilash Patil
Keyword(s):  
Steady State ◽  
Cfd Simulation ◽  
Cfd Analysis ◽  
Turbine Stage ◽  
Perfect Gas ◽  
Lower Efficiency ◽  
Real Gas ◽  
Stage Performance ◽  
The Impact ◽  
Stage Efficiency

CFD analysis has already been established as a preferred way of evaluating turbine stage performance and any incremental increase to it through component design changes. The usually overlooked assumption during a CFD simulation is the choice of gas model. In turbomachinery analysis, for quick assessment of stage performance, modeling the fluid as perfect gas has been yielding fairly reliable results. In general the consideration of real gas effects has been less popular; although they are more realistic. The paper presents the comparison of aero-thermal predictions of an un-cooled turbine stage using ideal and real gas models based on CFD studies only. In addition, the impact of gas models on stage performance predicted using steady state and unsteady CFD analysis is also presented. Based on steady state CFD evaluations, the stage efficiency variation with the change of gas model is less than 0.3% with the real gas effect indicating lower efficiency. However, the unsteady predictions indicate that the time averaged stage efficiency predicted using perfect gas model can be 1% higher than that predicted using real gas model.

Effect of Various Tip Clearance Squealer Design on Turbine Stage Efficiency

2015 ◽  
Author(s):  
Nikolay Lomakin ◽  
Andrey Granovskiy ◽  
Vladimir Shchaulov ◽  
Jaroslaw Szwedowicz
Keyword(s):  
Tip Clearance ◽  
Navier Stokes ◽  
Radial Clearance ◽  
Turbine Stage ◽  
Test Rig ◽  
Numerical Investigations ◽  
Blade Cascade ◽  
The Impact ◽  
Stage Efficiency ◽  
Insight Into

This paper presents investigation of nine tip squealer design variants based on full 3D Navier-Stokes CFD calculations. In particular two main design features have been studied: the impact of relative squealer cavity rim extension and the impact of pressure side squealer cavity rim inclination on stage efficiency. All these cases have been compared for two values of relative radial gaps 0.6% and 1.36%. Obtained numerical results were validated against the experimental data measured on the E3 blade cascade test rig given in the open literature. As the overall outcome for these numerical investigations two zones with different vortex structures and different sealing features have been found. Moreover the size of these zones determines the level of the tip clearance leakage and losses for various tip squealer designs. The obtained loss values and corresponding change of the stage efficiency level as well as flow structure details were compared for all studied cases, providing insight into turbine stage aerodynamics with respect to minimal and maximal radial clearance.

Design Considerations for Axial Steam Turbine Rotor Inlet Cavity Volume and Length Scale

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Konstantinos G. Barmpalias ◽  
Reza S. Abhari ◽  
Anestis I. Kalfas ◽  
Toshio Hirano ◽  
Naoki Shibukawa ◽  
...  
Keyword(s):  
Computational Analysis ◽  
Turbine Rotor ◽  
Volume Reduction ◽  
Length Scale ◽  
Toroidal Vortex ◽  
Cavity Volume ◽  
Design Considerations ◽  
Baseline Case ◽  
Design Perspective ◽  
Reduction Case

In this paper we examine the interaction between the cavity and main flows of three different rotor cavities. For each of the three rotor cavities, the cavity inlets differ in their axial cavity lengths, which are modified by extending the upper casing stator platform. The three cavity volumes are comprised of a baseline case, along with a 14% and a 28% volume reduction relative to the baseline case. Measurements show that there is an increase in efficiency of 0.3% for the 14% cavity volume reduction case (relative to the baseline case), whereas a further volume reduction of 28% (relative to the baseline case) decreases the efficiency. Computational analysis highlights the breakup of a toroidal vortex within the cavity as the primary factor explaining the changes in efficiency. The dominant cavity vortex originally present in the baseline case firstly broken up into two smaller vortices for the 14% cavity volume reduction case and secondly, completely replaced with a strong radial jet for the 28% volume reduction case. From a design perspective, reducing the cavity volume by extending the upper casing stator platform yields improvements in efficiency provided that the cavity vortex is still present. The design considerations, analysis and the associated aerodynamics are discussed in detail within this paper.

Experimental Investigation of Purge Flow Effects on a High Pressure Turbine Stage

2012 ◽  
Author(s):  
K. Regina ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
High Pressure ◽  
Mass Flow ◽  
Radial Displacement ◽  
Turbine Stage ◽  
Test Configuration ◽  
Flow Factor ◽  
Passage Vortex ◽  
Purge Flow ◽  
The Impact ◽  
Stage Efficiency

In the present paper an experimental investigation of the effects of hub purge flow on the performance of a high pressure axial turbine stage is presented. The test configuration consists of a one-and-a-half stage, unshrouded, highly loaded axial turbine, with a blading representative of high pressure gas turbines. The test configuration has the capability of integrating purge flow from the cavity under the rotor/stator platform. Efficiency measurements for various purge flow injection levels have been carried out with pneumatic probes at the exit of the rotor and show a reduction of isentropic total-to-total efficiency of 0.8 % per percent of injected mass flow. For three purge flow conditions the unsteady aerodynamic flow field at rotor inlet and rotor exit has been measured with the in-house developed Fast Response Aerodynamic Probe (FRAP): one condition is with sucking at a mass flow fraction of −0.1 % and two conditions are with injection at a mass flow fraction of 0.8 % and 1.2 %. The time-resolved data shows the unsteady interaction of the purge flow with the secondary flows of the main flow and the impact on the radial displacement of the rotor hub passage vortex. Steady measurements at off-design conditions show the impact of the rotor incidence and of the stage flow factor on the resulting stage efficiency and the radial displacement of the rotor HPV. A comparison of the effect of purge flow and of the off-design conditions on the rotor incidence and stage flow factor shows that the detrimental effect of the purge flow on the stage efficiency caused by the radial displacement of the rotor hub passage vortex is dominated by the increase of stage flow factor in the hub region rather than by the increase of negative rotor incidence.

Computational Analysis of Olfactory Airspace in Patients With Unilateral Cleft Lip Nasal Deformity

2020 ◽  
pp. 105566562098275
Author(s):  
Reanna Shah ◽  
Jeffrey R. Marcus ◽  
Dennis O. Frank-Ito
Keyword(s):  
Cleft Lip ◽  
Computational Analysis ◽  
Normal Subjects ◽  
Nasal Deformity ◽  
Normal Anatomy ◽  
3 Dimensional ◽  
Computed Tomography Images ◽  
High Prevalence ◽  
Dimensional Reconstruction ◽  
The Impact

Objectives: To evaluate the magnitude of olfactory recess opacity in patients with unilateral cleft lip nasal deformity (uCLND). Design: Subject-specific 3-dimensional reconstruction of the nasal airway anatomy was created from computed tomography images in 11 (4 males and 7 females) subjects with uCLND and 7 (3 males, and 4 females) normal subjects. The volume and surface area of each subject’s unilateral and bilateral olfactory airspace was quantified to assess the impact of opacification. Qualitatively speaking, patients with 75% to 100% olfactory recess opacification were classified as extreme, 50% to 75% as severe, 25% to 50% as moderate, and 0% to 25% as mild. Results: Of the 11 subjects with uCLND, 5 (45%) were classified as having extreme olfactory recess opacification, 3 (27%) subjects had severe opacification, and 3 (27%) subjects had moderate opacification. Mean (±SD) bilateral olfactory recess volume was significantly greater in normal subjects than in subjects with uCLND (0.9668 cm3 ± 0.4061 cm3 vs 0.3426 cm3 ± 0.1316 cm3; P < .001). Furthermore, unilateral olfactory airspace volumes for the cleft and non-cleft sides in subjects with uCLND were considerably less than unilateral olfactory volume in subjects with normal anatomy (uCLND cleft side = 0.1623 cm3 ± 0.0933 cm3; uCLND non-cleft side = 0.1803 cm3 ± 0.0938 cm3; normal = 0.4834 cm3 ± 0.2328 cm3; P < .001). Conclusions: Our findings indicate a high prevalence of olfactory recess opacification among subjects with uCLND when compared to subjects with normal anatomy. The majority of subjects with uCLND had extreme olfactory recess opacity, which will likely influence their sense of smell.

Overview of the Patient Perspective at OMERACT 10 — Conceptualizing Methods for Developing Patient-Reported Outcomes

2011 ◽  
Vol 38 (8) ◽  
pp. 1699-1701 ◽  
Author(s):  
JOHN R. KIRWAN ◽  
PETER S. TUGWELL
Keyword(s):  
Clinical Trials ◽  
Experimental Work ◽  
Patient Reported Outcomes ◽  
Patient Perspective ◽  
Methodological Issues ◽  
Instrument Selection ◽  
Patient Reported ◽  
The Impact ◽  
Choice Of Instruments ◽  
The Way

This overview draws out the main conclusions from the 4 workshops focused on incorporating the patient perspective into outcome assessment at the 10th Outcome Measures in Rheumatology (OMERACT 10) conference. They raised methodological issues about the choice of outcome domains to include in clinical trials, the development or choice of instruments to measure these domains, and the way these instruments might capture the impact of a disease and its treatment. The need to develop a more rigorous conceptual model of quantifying the way conditions affect health, and the need to ensure patients are directly involved in the decisions about domains and instruments, emerged clearly. The OMERACT participants voted to develop guidelines for domain and instrument selection, and conceptual and experimental work will be brought forward to revise and upgrade the OMERACT Filter.

scholarly journals The impact of atmospheric stability and wind shear on vertical cloud overlap over the Tibetan Plateau

2018 ◽  
Vol 18 (10) ◽  
pp. 7329-7343 ◽  
Author(s):  
Jiming Li ◽  
Qiaoyi Lv ◽  
Bida Jian ◽  
Min Zhang ◽  
Chuanfeng Zhao ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Wind Shear ◽  
Cloud Cover ◽  
Atmospheric Stability ◽  
Length Scale ◽  
The Tibetan Plateau ◽  
Total Cloud Cover ◽  
Atmospheric Models ◽  
The Impact ◽  
Overlap Parameter

Abstract. Studies have shown that changes in cloud cover are responsible for the rapid climate warming over the Tibetan Plateau (TP) in the past 3 decades. To simulate the total cloud cover, atmospheric models have to reasonably represent the characteristics of vertical overlap between cloud layers. Until now, however, this subject has received little attention due to the limited availability of observations, especially over the TP. Based on the above information, the main aim of this study is to examine the properties of cloud overlaps over the TP region and to build an empirical relationship between cloud overlap properties and large-scale atmospheric dynamics using 4 years (2007–2010) of data from the CloudSat cloud product and collocated ERA-Interim reanalysis data. To do this, the cloud overlap parameter α, which is an inverse exponential function of the cloud layer separation D and decorrelation length scale L, is calculated using CloudSat and is discussed. The parameters α and L are both widely used to characterize the transition from the maximum to random overlap assumption with increasing layer separations. For those non-adjacent layers without clear sky between them (that is, contiguous cloud layers), it is found that the overlap parameter α is sensitive to the unique thermodynamic and dynamic environment over the TP, i.e., the unstable atmospheric stratification and corresponding weak wind shear, which leads to maximum overlap (that is, greater α values). This finding agrees well with the previous studies. Finally, we parameterize the decorrelation length scale L as a function of the wind shear and atmospheric stability based on a multiple linear regression. Compared with previous parameterizations, this new scheme can improve the simulation of total cloud cover over the TP when the separations between cloud layers are greater than 1 km. This study thus suggests that the effects of both wind shear and atmospheric stability on cloud overlap should be taken into account in the parameterization of decorrelation length scale L in order to further improve the calculation of the radiative budget and the prediction of climate change over the TP in the atmospheric models.

Effect of Wake Passing on Unsteady Aerodynamic Performance in a Turbine Stage

2006 ◽  
Author(s):  
K. Yamada ◽  
K. Funazaki ◽  
K. Hiroma ◽  
M. Tsutsumi ◽  
Y. Hirano ◽  
...  
Keyword(s):  
Secondary Flow ◽  
Three Dimensional ◽  
Suction Side ◽  
Turbine Stage ◽  
Three Dimensional Flow ◽  
Unsteady Aerodynamic ◽  
Unsteady Effect ◽  
Unsteady Rans ◽  
Wake Passing ◽  
Stage Efficiency

In the present work, unsteady RANS simulations were performed to clarify several interesting features of the unsteady three-dimensional flow field in a turbine stage. The unsteady effect was investigated for two cases of axial spacing between stator and rotor, i.e. large and small axial spacing. Simulation results showed that the stator wake was convected from pressure side to suction side in the rotor. As a result, another secondary flow, which counter-rotated against the passage vortices, was periodically generated by the stator wake passing through the rotor passage. It was found that turbine stage efficiency with the small axial spacing was higher than that with the large axial spacing. This was because the stator wake in the small axial spacing case entered the rotor before mixing and induced the stronger counter-rotating vortices to suppress the passage vortices more effectively, while the wake in the large axial spacing case eventually promoted the growth of the secondary flow near the hub due to the migration of the wake towards the hub.

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