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

2016 ◽  
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.

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

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Johan Dahlqvist ◽  
Jens Fridh
Keyword(s):  
Mach Number ◽  
Flow Field ◽  
High Speed ◽  
Negative Impact ◽  
Spatial Average ◽  
Turbine Stage ◽  
Flow Angle ◽  
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 cavities below the hub level from the hot main annulus flow. 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 design case, and two high-speed points encompassing the peak efficiency. At each of these operating speeds, the amount of purge flow was varied from 0% to 2%. Observing the effect of the purge rate on measurement plane averaged parameters, a minor flow angle decrease and Mach number increase is seen for the low speed case, while maintaining near constant values for the higher operating speeds. The prominent effect due to purge is seen in the efficiency, showing a linear sensitivity to purge of 1.3%-points for every 1% of added purge flow for the investigated speeds. While spatial average values of flow angle 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 at higher span, with associated decreased turning. A radial efficiency distribution is utilized, showing negative impact through span heights from 15% to 70%. Pitchwise variation of investigated flow parameters is significantly influenced by purge flow, making this a parameter to include for instance when evaluating benefits of stator clocking positions.

Seedgas Investigation of Turbine Stage and Seal Performance at Varying Cavity Purge Rates and Operating Speeds

2017 ◽  
Author(s):  
Johan Dahlqvist ◽  
Jens Fridh
Keyword(s):  
Boundary Layers ◽  
High Speed ◽  
Side Wall ◽  
Turbine Stage ◽  
Performance Impact ◽  
Cooling Performance ◽  
Wide Range ◽  
Loading Case ◽  
Purge Flow ◽  
Flow Through

The topic of hub cavity purge is investigated in a high-pressure axial low-reaction turbine stage. Both the sealing ability of the purge flow and the performance impact associated with its injection into the main flow are studied. Three operating speeds are investigated, namely a high loading case, the peak efficiency, and a high speed case, and purge flow rates across a wide range. The operating points coincide with investigations previously reported, where the flow field and stage efficiency was quantified using pneumatic probes. Comparative measurements are also performed, varying a leakage flow through the rotor below the hub platform. The purge flow is now seeded with CO2 in order to measure its distribution throughout the stage, as it is injected into the wheelspace upstream of the rotor, allowing for quantification of the sealing effectiveness. This is done at a number of defined locations along the stator-side wall in the wheel space, resolving the radial variation through the cavity. Important radial variations of effectiveness are observed, confirming that the flow is in the regime of merged boundary layers, due to the narrow cavity, as compared to typical gas turbine operation with separated boundary layers. The trends are found to be related to operating speed and platform leakage. With known sealing effectiveness, industry correlations may be adapted to make use of the variation of necessary purge rate to obtain a certain degree of sealing at a given operating point, and thereby optimize the efficiency. In addition to quantification of potential hot-gas ingestion, the paper initiates an investigation of the transport of the purge flow in the main annulus, through sampling on the hub, as well as area traverse downstream of the rotor. The amount of sealing gas leads to opportunity to quantify the cooling performance of the purge flow in the main annulus. Both the cooling performance in the main annulus and cavity are shown to be significantly influenced by the rotor leakage, while its effect on efficiency is minor.

scholarly journals Characterization of Periodic Incoming Wakes in a Low-Pressure Turbine Cascade Test Section by Means of a Fast-Response Single Sensor Virtual Three-Hole Probe

2019 ◽  
Vol 4 (3) ◽  
pp. 26
Author(s):  
Julien Clinckemaillie ◽  
Tony Arts
Keyword(s):  
Total Pressure ◽  
High Speed ◽  
Control Volume ◽  
Low Pressure ◽  
Fast Response ◽  
Pressure Probe ◽  
Flow Angle ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Good Agreement

This paper aims at evaluating the characteristics of the wakes periodically shed by the rotating bars of a spoked-wheel type wake generator installed upstream of a high-speed low Reynolds linear low-pressure turbine blade cascade. Due to the very high bar passing frequency obtained with the rotating wake generator (fbar = 2.4−5.6 kHz), a fast-response pressure probe equipped with a single 350 mbar absolute Kulite sensor has been used. In order to measure the inlet flow angle fluctuations, an angular aerodynamic calibration of the probe allowed the use of the virtual three-hole mode; additionally, yielding yaw corrected periodic total pressure, static pressure and Mach number fluctuations. The results are presented for four bar passing frequencies (fbar = 2.4/3.2/4.6/5.6 kHz), each tested at three isentropic inlet Mach numbers M1,is = 0.26/0.34/0.41 and for Reynolds numbers varying between Re1,is = 40,000 and 58,000, thus covering a wide range of engine representative flow coefficients (ϕ = 0.44−1.60). The measured wake characteristics show fairly good agreement with the theory of fixed cylinders in a cross-flow and the evaluated total pressure losses and flow angle variations generated by the rotating bars show fairly good agreement with theoretical results obtained from a control volume analysis.

The Effect of Secondary Air Injection on the Performance of a Transonic Turbine Stage

2002 ◽  
Author(s):  
S. Girgis ◽  
E. Vlasic ◽  
J.-P. Lavoie ◽  
S. H. Moustapha
Keyword(s):  
Turbine Stage ◽  
Cfd Simulations ◽  
Secondary Air Injection ◽  
Flow Test ◽  
Mainstream Flow ◽  
Purge Flow ◽  
Simulated Test ◽  
Transonic Turbine ◽  
Secondary Air ◽  
Stage Efficiency

This paper presents results of rig testing of a transonic, single stage turbine with various modifications made to the injection of secondary air into the mainstream. Results show that significant improvements in stage efficiency can be realized by optimizing the injection of upstream disk purge and rotor upstream shroud leakage flow into the mainstream flow. Results of CFD simulations of the rotor upstream disk purge flow test conditions and closely simulated test geometry agree well with test data.

scholarly journals Test Facility for High-Speed Probe Calibration

2019 ◽  
Vol 213 ◽  
pp. 02033
Author(s):  
Tomáš Jelínek ◽  
Erik Flídr ◽  
Martin Němec ◽  
Jan Šimák
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Total Pressure ◽  
High Speed ◽  
Test Facility ◽  
Nozzle Outlet ◽  
Wide Range ◽  
Mach Numbers ◽  
Probe Calibration ◽  
Subsonic Nozzle

A new test facility was built up as a part of a closed-loop transonic wind tunnel in VZLU´s High-speed Aerodynamics Department. The wind tunnel is driven by a twelve stage radial compressor and Mach and Reynolds numbers can be changed by the compressor speed and by the total pressure in the wind tunnel loop by a set of vacuum pumps, respectively. The facility consists of an axisymmetric subsonic nozzle with an exit diameter de = 100 mm. The subsonic nozzle is designed for regimes up to M = 1 at the nozzle outlet. At the nozzle inlet there is a set of a honeycomb and screens to ensure the flow stream laminar at the outlet of the nozzle. The subsonic nozzle can be supplemented with a transonic slotted nozzle or a supersonic rigid nozzle for transonic and supersonic outlet Mach numbers. The probe is fixed in a probe manipulator situated downstream of the nozzle and it ensures a set of two perpendicular angles in a wide range (±90°). The outlet flow field was measured through in several axial distances downstream the subsonic nozzle outlet. The total pressure and static pressure was measured in the centreline and the total pressure distribution in the vertical and horizontal plane was measured as well. Total pressure fluctuations in the nozzle centreline were detected by a FRAP probe. From the initial flow measurement in a wide range of Mach numbers the best location for probe calibration was chosen. The flow field was found to be suitable for probe calibration.

Theoretical Distributions of Heat Transfer Downstream of a Backstep in Supersonic Turbulent Flow

1972 ◽  
Vol 94 (1) ◽  
pp. 87-94 ◽  
Author(s):  
J. P. Lamb ◽  
C. G. Hood
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulent Flow ◽  
Wall Temperature ◽  
Control Volume ◽  
Convective Transport ◽  
Transport Processes ◽  
Independent Variables ◽  
Test Conditions ◽  
Wide Range

A physically perceptive model is presented for the flow field and convective transport processes in the vicinity of reattachment of a planar, supersonic, turbulent flow. Control volume methods are utilized extensively in the analysis and the restating integral equations are solved by various numerical search techniques. The analysis enables one to determine significant parameters in the flow field as well as the heat transfer distribution and associated wall temperature of the reattachment surface. Also presented is a general correlation of predicted results for the convection process in terms of pertinent independent variables. The correlated results are shown to agree with measurements for a wide range of test conditions.

Numerical Investigations on the Aerodynamic Performance and Endwall Cooling Characteristics of Turbine During Acceleration Process With Lagging Effects

2021 ◽  
Author(s):  
Qingfeng Cong ◽  
Zhigang Li ◽  
Jun Li
Keyword(s):  
Flow Field ◽  
Rotational Speed ◽  
Aerodynamic Performance ◽  
Acceleration Process ◽  
Two Stage ◽  
Cooling Effectiveness ◽  
Mainstream Flow ◽  
Purge Flow ◽  
Secondary Air ◽  
Endwall Cooling

Abstract In the process of turbine acceleration, due to the influence of compressor and complex secondary air system, the change process of coolant purge flow is relatively lagging behind that of mainstream flow and rotational speed. The lagging egress of coolant flow influence the aerodynamic performance and endwall cooling effectiveness of turbine acceleration process. The flow field and aerothermal performance of two-stage axial turbines combined with rim seal structures and coolant purge flow lagging effects in the turbine acceleration process was numerically investigated using Unsteady Reynolds-Averaged Navier-Stokes (URANS) via SST turbulence model. The effects of lagging coolant purge flow across the rim seal on the turbine aerodynamics and endwall cooling effectiveness were analyzed. The obtained results show that the turbine aerodynamic efficiency obtains the maximum value when the coolant purge flow lagging time equals to half the acceleration time at the same rotational speed after the end of lagging times. The total-to-total efficiency for the second stage is more sensitive to lagging times. The turbine output power is almost un-changed due to combination of additional work capacity and aerodynamic loss with the introduction of coolant. The turbine endwalls have the maximum averaged cooling effectiveness in the turbine acceleration process without consideration of the coolant purge flow lagging time. And endwall cooling effectiveness decreases with the increase of coolant purge flow lagging time at the same rotational speed and mainstream flow conditions. The detailed flow field of two-stage turbine considering interaction between the coolant purge flow and mainstream was also discussed. The present work provides the reference for the match design between the turbine mainstream flow and secondary air flow system.

scholarly journals Heat Transfer Behaviour and Flow Field Characterisation of Impinging Synthetic Jets for a Wide Range of Parameters

2010 ◽  
Author(s):  
Rayhaan Farrelly ◽  
Alan McGuinn ◽  
Tim Persoons ◽  
Darina Murray
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
High Speed ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Local Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Flow Measurements ◽  
Wide Range

Impinging synthetic jets are considered as a potential solution for convective cooling, in applications that match their main characteristics (high local heat transfer rates, zero net mass flux, scalability, active control). Nevertheless the understanding of heat transfer to synthetic jets falls short of that available for steady jets. To address this, this paper uses detailed flow field measurements to help identify the main heat transfer mechanisms in impinging synthetic jets. Local heat transfer measurements have been performed for an impinging round synthetic jet at a range of Reynolds numbers between 1000 and 3000, nozzle to plate spacings between 4D and 16D and stroke lengths (L0) between 2D and 32D. The heat transfer results show evidence of distinct regimes in terms of L0/D and L0/H ratios. Based on appropriate scaling, four heat transfer regimes are identified which justifies a detailed study of the flow field characteristics. High speed particle image velocimetry (PIV) has been employed to measure the time-resolved velocity flow fields of the synthetic jet to identify the flow structures at selected L0/H values corresponding to the identified heat transfer regimes. The flow measurements support the same regimes as identified from the heat transfer measurements and provide physical insight for the heat transfer behaviour.

Experimental and Numerical Investigation of the Flow Field at Radial Holes in High-Speed Rotating Shafts

2012 ◽  
Author(s):  
Jan Sousek ◽  
Daniel Riedmüller ◽  
Michael Pfitzner
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Discharge Coefficient ◽  
Cross Flow ◽  
Test Rig ◽  
Flow Phenomena ◽  
Rotating Shafts ◽  
Secondary Air ◽  
The One ◽  
Discharge Behaviour

Rotating and stationary orifices are used within the secondary air system to transport sealing/ cooling air to its consumers. This paper reports on measurements of the discharge coefficient of rotating radial holes as their aerodynamical behaviour is different from the one of axial or stationary holes due to the presence of centrifugal and Coriolis forces. A test rig containing two independently rotating shafts was designed to investigate the flow phenomena and the discharge behaviour of these orifices. The required air mass flow is delivered by a screw compressor and can be regulated independently to supply the inner and outer annular passages of the test rig. It allows measurements of the discharge coefficient with cross flow and co- and counter-rotating shafts with centrifugal and centripetal flow through the rotating holes. On the outer shaft, absolute and differential pressures and temperatures in the rotating frame of reference are measured via a telemetry system. Measurements of the discharge coefficient for sharp-edged and rounded shaft inserts at a variety of different flow conditions and with swirl added to the air upstream of the orifice are presented. Furthermore experiments were conducted to quantify the influence of the inner shaft (non-rotating and rotating) on the discharge behaviour of orifices in the outer shaft. To complement the data acquired from the experiments and to get a better understanding of the flow field near the rotating holes also numerical flow simulations were performed.

Sign in / Sign up

Export Citation Format

Share Document