Experimental Study of Ingestion in the Rotor-Stator Disk Cavity of a Subscale Axial Turbine Stage

While it is widely recognized that ingestion of hot gas from the main annulus of axial gas turbine stages into rotor-stator disk cavities depend strongly on the unsteadiness of the prevailing flow field, the large computational effort needed to simulate the flow field renders its use in the design of turbine internal air system and seals difficult. As an alternative, considerable effort has been devoted in recent years to develop simple orifice models of disk cavity rim seals based on time-averaged flow information; these models contain empirical discharge coefficients for ingestion into and egress from the cavities. The present experimental work in a subscale axial turbine stage reports a simple orifice model of an axially-overlapping radial-clearance seal at the disk cavity rim and values of the discharge coefficients over a range of purge flow rate supplied to the cavity. In the experiments, the ingestion process was dominated by the main gas annulus flow. Time-averaged static pressure distribution was measured in the main annulus and in the disk cavity; the driving force for ingestion and egress was taken to be the pressure differential between the main annulus and the rim cavity at prescribed locations. Time-averaged ingestion was measured using the tracer gas technique; the pressure and ingestion data were combined to obtain the ingestion and egress discharge coefficients at several purge flow rates. The location on the vane platform 1mm upstream of its lip represented the main gas annulus pressure in the calculation of discharge coefficients. In the rim cavity, two locations on the stator, one in the ‘seal region’ and the other slightly inward radially, were prescribed to represent the rim cavity pressure as well as the sealing effectiveness. Two corresponding sets of ingestion and egress discharge coefficients are reported for the various purge flow rates. The ingestion discharge coefficient obtained using the seal region location in the rim cavity decreased as the purge flow rate increased; the corresponding egress discharge coefficient increased with purge flow rate. For the rim cavity location slightly inward radially from the seal region, the egress discharge coefficient maintained the same trend; however, the ingestion discharge coefficient decreased only slightly as the purge flow rate increased. It is suggested that the seal region location in the rim cavity is the more appropriate location in calculating the rim seal discharge coefficients. The ratio of ingestion to egress discharge coefficients exhibited considerable variation with purge flow rate.

Download Full-text

Experimental Study of Ingestion in the Rotor–Stator Disk Cavity of a Subscale Axial Turbine Stage

Journal of Turbomachinery ◽

10.1115/1.4030099 ◽

2015 ◽

Vol 137 (9) ◽

Cited By ~ 8

Author(s):

J. Balasubramanian ◽

P. S. Pathak ◽

J. K. Thiagarajan ◽

P. Singh ◽

R. P. Roy ◽

...

Keyword(s):

Flow Rate ◽

Discharge Coefficient ◽

Labyrinth Seal ◽

The Other ◽

Radial Clearance ◽

Cavity Pressure ◽

Turbine Stage ◽

Axial Turbine ◽

Discharge Coefficients ◽

Purge Flow

This paper describes experiments in a subscale axial turbine stage equipped with an axially overlapping radial-clearance seal at the disk cavity rim and a labyrinth seal radially inboard which divides the disk cavity into a rim cavity and an inner cavity. An orifice model of the rim seal is presented; values of ingestion and egress discharge coefficients based on the model and experimental data are reported for a range of cavity purge flow rate. In the experiments, time-averaged pressure distribution was measured in the main gas annulus and in the disk cavity; also measured was the time-averaged ingestion into the cavity. The pressure and ingestion data were combined to obtain the discharge coefficients. Locations on the vane platform 1 mm upstream of its lip over two vane pitches circumferentially defined the main gas annulus pressure; in the rim cavity, locations at the stator surface in the radially inner part of the “seal region” over one vane pitch defined the cavity pressure. For the sealing effectiveness, two locations in the rim cavity at the stator surface, one in the “mixing region” and the other radially further inward at the beginning of the stator boundary layer were considered. Two corresponding sets of ingestion and egress discharge coefficients are reported. The ingestion discharge coefficient was found to decrease in magnitude as the purge flow rate increased; the egress discharge coefficient increased with purge flow rate. The discharge coefficients embody fluid-mechanical effects in the ingestion and egress flows. Additionally, the minimum purge flow rate required to prevent ingestion was estimated for each experiment set and is reported. It is suggested that the experiments were in the combined ingestion (CI) region with externally induced (EI) ingestion being the dominant contributor.

Download Full-text

Deterministic Decomposition of the Unsteady Flow in a Unidirectional Axial Turbine for OWC Plant

Volume 10: Ocean Renewable Energy ◽

10.1115/omae2018-78650 ◽

2018 ◽

Author(s):

Nuria Alvarez Bertrand ◽

Jesús Manuel Fernández Oro ◽

Bruno Pereiras García ◽

Manuel García Díaz

Keyword(s):

Flow Rate ◽

High Efficiency ◽

Low Flow ◽

Oscillating Water Column ◽

Turbine Stage ◽

Flow Rates ◽

Aerodynamic Efficiency ◽

Axial Turbine ◽

Deterministic Framework ◽

Energy Plants

The “twin-turbine” configuration has recently emerged as a feasible possibility for unidirectional turbines to be introduced in Oscillating Water Column wave energy plants without requiring auxiliary rectifying systems. Previous investigations by the authors have been focused on the development of a numerical CFD model to analyze the performance of a unidirectional axial turbine for twin turbine configuration in an OWC system. In this paper, all these numerical databases are further post-processed using a deterministic framework to give more insight about the flow patterns within the turbine. The final objective is the analysis of the unsteady features of the flow and the stator-rotor interactions using a deterministic decomposition. The present study reveals that levels of deterministic unsteadiness in the inter-row region are moderate, being more intense as the flow rate is decreased. Turbulence intensities are also observed to be clearly prominent in case of lower flow rates. Although these findings appear to be contradictory with the high-efficiency low flow rates of the turbine, the major levels of stator-rotor unsteadiness at higher flow rates (shown by the deterministic decomposition) justify the serious penalty in the aerodynamic efficiency as the turbine flow rate is increased. Finally, some advices with respect the design of the vane row in the turbine stage are given to control the generation of turbulence and stator-rotor interaction.

Download Full-text

Experimental Study on Discharge Coefficients of Windward Window in Buildings with Wind-Driven Cross Ventilation

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1008-1009.1061 ◽

2014 ◽

Vol 1008-1009 ◽

pp. 1061-1067

Author(s):

Qiao Ning Wang ◽

Yan Ling Guan ◽

Qi Hai Liao

Keyword(s):

Flow Rate ◽

Natural Ventilation ◽

Discharge Coefficient ◽

Static Pressure ◽

Flow Rates ◽

Discharge Coefficients ◽

Window Opening ◽

Static Pressure Difference ◽

Window Area ◽

The Impact

Focus on the prediction of flow rates in buildings under natural ventilation, the investigation conducted a series of model rooms with cross ventilation. The impact of window-wall ratios, windows configurations as well as corresponding flow rates was investigated. The object of this investigation is to analyze characteristics of windward window opening discharge coefficient by measuring static pressure difference and the flow rate through windows. The conclusion are as follows: For large openings, the discharge coefficient of windward window opening increases as the window-wall ratio grows up; With windward window-wall ratio of 44.4% and 11.1%, the discharge coefficient of windward openings is almost irrelevant to flow rate and less affected by leeward window area; However, with windward window-wall ratio of 2.78%, the discharge coefficient increases slightly as flow rate rises, and the larger the area of leeward opening is, the smaller the discharge coefficient of windward opening becomes.

Download Full-text

Experimental Investigation of Turbine Stage Flow Field and Performance at Varying Cavity Purge Rates and Operating Speeds

Volume 2B: Turbomachinery ◽

10.1115/gt2016-57735 ◽

2016 ◽

Cited By ~ 4

Author(s):

Johan Dahlqvist ◽

Jens Fridh

Keyword(s):

Mach Number ◽

Flow Field ◽

High Speed ◽

Control Volume ◽

Spatial Average ◽

Turbine Stage ◽

Wide Range ◽

Annulus Flow ◽

Purge Flow ◽

Secondary Air

The aspect of hub cavity purge has been investigated in a high-pressure axial low-reaction turbine stage. The cavity purge is an important part of the secondary air system, used to isolate the hot main annulus flow from cavities below the hub level. A full-scale cold-flow experimental rig featuring a rotating stage was used in the investigation, quantifying main annulus flow field impact with respect to purge flow rate as it was injected upstream of the rotor. Five operating speeds were investigated of which three with respect to purge flow, namely a high loading case, the peak efficiency, and a high speed case. At each of these operating speeds, the amount of purge flow was varied across a very wide range of ejection rates. Observing the effect of the purge rate on measurement plane averaged parameters, a minor outlet swirl decrease is seen with increasing purge flow for each of the operating speeds while the Mach number is constant. The prominent effect due to purge is seen in the efficiency, showing a similar linear sensitivity to purge for the investigated speeds. An attempt is made to predict the efficiency loss with control volume analysis and entropy production. While spatial average values of swirl and Mach number are essentially unaffected by purge injection, important spanwise variations are observed and highlighted. The secondary flow structure is strengthened in the hub region, leading to a generally increased over-turning and lowered flow velocity. Meanwhile, the added volume flow through the rotor leads to higher outlet flow velocities visible in the tip region, and an associated decreased turning. A radial efficiency distribution is utilized, showing increased impact with increasing rotor speed.

Download Full-text

Effects of Cavity Purge Flow on Intermediate Turbine Duct Flowfield

Volume 2B: Turbomachinery ◽

10.1115/gt2018-76324 ◽

2018 ◽

Author(s):

Jun Liu ◽

Qiang Du ◽

Guang Liu ◽

Pei Wang ◽

Hongrui Liu ◽

...

Keyword(s):

Flow Field ◽

Flow Rate ◽

Design Criterion ◽

Operating Conditions ◽

Duct Flow ◽

Intermediate Turbine Duct ◽

Low Pressure Turbine ◽

Cavity Structure ◽

Flow Mechanisms ◽

Purge Flow

To increase the power output without adding additional stages, ultra-high bypass ratio engine, which has larger diameter low pressure turbine, attracts more and more attention because of its huge advantage. This tendency will lead to aggressive (high diffusion) intermediate turbine duct design. Much work has been done to investigate flow mechanisms in this kind of duct as well as its design criterion with numerical and experimental methods. Usually intermediate turbine duct simplified from real engine structure was adopted with upstream and downstream blades. However, cavity purge mass flow exists to disturb the duct flow field in real engine to change its performance. Naturally, the wall vortex pairs would develop in different ways. In addition to that, purge flow rate changes at different engine representative operating conditions. This paper deals with the influence of turbine purge flow on the aerodynamic performance of an aggressive intermediate turbine duct. The objective is to reveal the physical mechanism of purge flow ejected from the wheel-space and its effects on the duct flow field. Ten cases with and without cavity are simulated simultaneously. On one hand, the influence of cavity structure without purge flow on the flow field inside duct could be discussed. On the other hand, the effect of purge flow rate on flow field could be analyzed to investigate the mechanisms at different engine operating conditions. According to this paper, cavity structure is beneficial for pressure loss. And the influence concentrates near hub and duct inlet.

Download Full-text

Numerical Studies on the Effect of Tip Clearance and Tip Cooling Flow on Endwall Losses of an Unshrouded Axial Turbine Rotor

ASME 2013 Gas Turbine India Conference ◽

10.1115/gtindia2013-3568 ◽

2013 ◽

Author(s):

K. Asgar Ali ◽

Quamber H. Nagpurwala ◽

Abdul Nassar ◽

S. V. Ramanamurthy

Keyword(s):

Flow Rate ◽

Layer Growth ◽

Coolant Flow ◽

Tip Clearance ◽

Coolant Flow Rate ◽

Total Efficiency ◽

Turbine Stage ◽

Suction Surface ◽

Axial Turbine ◽

Ejection Rate

This paper deals with the numerical investigations on a low pressure axial turbine stage to assess the effect of variation in rotor tip clearance and tip coolant ejection rate on the end wall losses. The rotor, along with the NGV, was modeled to represent the entire turbine stage. The CFX TASCflow software was used to perform steady state analysis for different rotor tip clearances and different tip coolant ejection rates. The locations of the cooling slots were identified on the blade tip and the coolant ejection rate was specified at these areas. The simulations were carried out with tip clearances of 0%, 1% and 2% of blade height and ejection flow rates of 0.5%, 0.75% and 1% of main turbine flow rate. It is shown that the size and strength of the leakage vortex is directly related to the tip clearance. The reduction in efficiency is not in linearity with the tip clearance owing to the effect of boundary layer growth on the end walls. Introduction of the tip coolant flow shows increased total–total efficiency compared to that of the uncooled tip. This is attributed to a reduction in the strength of the leakage vortex due to reduced cross-flow over the tip clearance from pressure surface to suction surface. At a coolant flow rate of 0.75% of the main flow rate, there is significant increase in efficiency of about 0.5%. Optimum tip clearance and coolant flow rate are obtained based on the results of the present analysis.

Download Full-text

Unsteady Turbine Rim Sealing and Vane Trailing Edge Flow Effects

10.1115/gt2021-59273 ◽

2021 ◽

Author(s):

Iván Monge-Concepción ◽

Shawn Siroka ◽

Reid A. Berdanier ◽

Michael D. Barringer ◽

Karen A. Thole ◽

...

Keyword(s):

Flow Field ◽

Unsteady Flow ◽

Rotational Speed ◽

Large Scale ◽

Trailing Edge ◽

Time Resolved ◽

Flow Rates ◽

Large Scale Structures ◽

Purge Flow ◽

Scale Structures

Abstract Hot gas ingestion into the turbine rim seal cavity is an important concern for engine designers. To prevent ingestion, rim seals use high pressure purge flow but excessive use of the purge flow decreases engine thermal efficiency. A single stage test turbine operating at engine-relevant conditions with real engine hardware was used to study time-resolved pressures in the rim seal cavity across a range of sealing purge flow rates. Vane trailing edge (VTE) flow, shown previously to be ingested into the rim seal cavity, was also included to understand its effect on the unsteady flow field. Measurements from high-frequency response pressure sensors in the rim seal and vane platform were used to determine rotational speed and quantity of large-scale structures (cells). In a parallel effort, a computational model using Unsteady Reynolds-averaged Navier-Stokes (URANS) was applied to determine swirl ratio in the rim seal cavity and time-resolved rim sealing effectiveness. The experimental results confirm that at low purge flow rates, the VTE flow influences the unsteady flow field by decreasing pressure unsteadiness in the rim seal cavity. Results show an increase in purge flow increases the number of unsteady large-scale structures in the rim seal and decreases their rotational speed. However, VTE flow was shown to not significantly change the cell speed and count in the rim seal. Simulations point to the importance of the large-scale cell structures in influencing rim sealing unsteadiness, which is not captured in current rim sealing predictive models.

Download Full-text

Aerodynamic Loss Characteristics of a Turbine Blade With Trailing Edge Coolant Ejection: Part 1—Effect of Cut-Back Length, Spanwise Rib Spacing, Free-Stream Reynolds Number, and Chordwise Rib Length on Discharge Coefficients

Journal of Turbomachinery ◽

10.1115/1.1348017 ◽

2000 ◽

Vol 123 (2) ◽

pp. 238-248 ◽

Cited By ~ 20

Author(s):

Oguz Uzol ◽

Cengiz Camci ◽

Boris Glezer

Keyword(s):

Reynolds Number ◽

Mass Flow Rate ◽

Flow Rate ◽

Discharge Coefficient ◽

Free Stream ◽

Cooling System ◽

Trailing Edge ◽

Discharge Coefficients ◽

Reynolds Number Dependency ◽

Spanwise Rib

The internal fluid mechanics losses generated between the blade plenum chamber and a reference point located just downstream of the trailing edge are investigated for a turbine blade trailing edge cooling system. The discharge coefficient Cd is presented as a function of the free-stream Reynolds number, cut-back length, spanwise rib spacing, and chordwise rib length. The results are presented in a wide range of coolant to free-stream mass flow rate ratios. The losses from the cooling system show strong free-stream Reynolds number dependency, especially at low ejection rates, when they are correlated against the coolant to free-stream pressure ratio. However, when Cd is correlated against a coolant to free-stream mass flow rate ratio, the Reynolds number dependency is eliminated. The current data clearly show that internal viscous losses due to varying rib lengths do not differ significantly. The interaction of the external wall jet in the cutback region with the free-stream fluid is also a strong contributor to the losses. Since the discharge coefficients do not have Reynolds number dependency at high ejection rates, Cd experiments can be performed at a low free-stream Reynolds number. Running a discharge coefficient experiment at low Reynolds number (or even in still air) will sufficiently define the high blowing rate portion of the curve. This approach is extremely time efficient and economical in finding the worst possible Cd value for a given trailing edge coolant system.

Download Full-text

Identification of Wake Convection and Flow Outline in the Interface Region of Blade Rows With Axial Gap in a Counter Rotating Turbine

Volume 1: Compressors, Fans, and Pumps; Turbines; Heat Transfer; Structures and Dynamics ◽

10.1115/gtindia2019-2634 ◽

2019 ◽

Author(s):

Rayapati Subbarao ◽

M. Govardhan

Keyword(s):

Flow Pattern ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Three Dimensional ◽

Interface Region ◽

Turbine Stage ◽

Deviation Angle ◽

Flow Rates ◽

Improved Performance

Abstract In a Counter Rotating Turbine (CRT), the stationary nozzle is trailed by two rotors that rotate in the opposite direction to each other. Flow in a CRT stage is multifaceted and more three dimensional, especially, in the gap between nozzle and rotor 1 as well as rotor 1 and rotor 2. By varying this gap between the blade rows, the flow and wake pattern can be changed favorably and may lead to improved performance. Present work analyzes the aspect of change in flow field through the interface, especially the wake pattern and deviation in flow with change in spacing. The components of turbine stage are modeled for different gaps between the components using ANSYS® ICEM CFD 14.0. Normalized flow rates ranging from 0.091 to 0.137 are used. The 15, 30, 50 and 70% of the average axial chords are taken as axial gaps in the present analysis. CFX 14.0 is used for simulation. At nozzle inlet, stagnation pressure boundary condition is used. At the turbine stage or rotor 2 outlet, mass flow rate is specified. Pressure distribution contours at the outlets of the blade rows describe the flow pattern clearly in the interface region. Wake strength at nozzle outlet is more for the lowest gap. At rotor 1 outlet, it is less for x/a = 0.3 and increases with gap. Incidence angles at the inlets of rotors are less for the smaller gaps. Deviation angle at the outlet of rotor 1 is also considered, as rotor 1-rotor 2 interaction is more significant in CRT. Deviation angle at rotor 1 outlet is minimum for this gap. Also, for the intermediate mass flow rate of 0.108, x/a = 0.3 is giving more stage performance. This suggests that at certain axial gap, there is better wake convection and flow outline, when compared to other gap cases. Further, it is identified that for the axial gap of x/a = 0.3 and the mean mass flow rate of 0.108, the performance of CRT is maximum. It is clear that the flow pattern at the interface is changing the incidence and deviation with change in axial gap and flow rate. This study is useful for the gas turbine community to identify the flow rates and gaps at which any CRT stage would perform better.

Download Full-text