Comparison of Discharge Coefficient Measurements and Correlations for Orifices With Cross-Flow and Rotation

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Marcus Hüning
Keyword(s):  
Gas Turbines ◽  
Discharge Coefficient ◽  
Computer Network ◽  
Cross Flow ◽  
Angular Speed ◽  
Component Design ◽  
Contour Plots ◽  
Secondary Air ◽  
Temperature Levels ◽  
Asme Paper

Gas turbines and jet engines consist of a network of connected cavities beside the main gas path called the secondary air system. These cavities, which are often surrounded by stationary and high angular speed rotating walls are exposed to varying pressure and temperature levels of air or oil contaminated air and are connected to each other by orifices or restrictors. It is vital to control the secondary flow to enable a reliable and efficient engine design, which meets component durability with a minimum of parasitic air consumption. It is essential to understand the flow physics as well as network interdependency in order to minimize the flow consumption and yet meeting engine operating requirements, as well as practical parts component design or manufacturing needs. In this connection, computer network codes containing model conceptions, which can accurately predict orifice flows, are essential. In an effort to provide usable further insight into flows across restrictors, such as orifices, this publication compares test results and orifice loss calculation models from the open literature with the aid of transformation laws and contour plots. The influence of different geometric features is incorporated into a model for the calculation of discharge coefficients. This publication is an extract of the underlying widespread and more detailed ASME paper (Huening, 2008, “Comparison of Discharge Coefficient Measurements and Correlations for Several Orifice Designs With Cross-Flow and Rotation Around Several Axes,” ASME Paper No. GT2008-50976). Minor errors, noticed during adapting, are corrected.

Comparison of Discharge Coefficient Measurements and Correlations for Several Orifice Designs With Cross-Flow and Rotation Around Several Axes

2008 ◽  
Author(s):  
M. Hu¨ning
Keyword(s):  
Gas Turbines ◽  
Computer Network ◽  
Cross Flow ◽  
Angular Speed ◽  
Jet Engines ◽  
Component Design ◽  
Engine Design ◽  
Contour Plots ◽  
Secondary Air ◽  
Temperature Levels

Gas turbines and jet engines consist of a network of connected cavities beside the main gas path, called secondary air system. These cavities, which are often surrounded by stationary and high angular speed rotating walls are exposed to varying pressure and temperature levels of air or oil contaminated air and are connected to each other by orifices or restrictors. It is vital to control the secondary flow, to enable a reliable and efficient engine design, which meets component durability with a minimum of parasitic air consumption. It is essential to understand the flow physics as well as network inter-dependency in order to minimise the flow consumption and yet, meeting engine operating requirements, as well as practical parts component design or manufacturing needs. In this connexion computer network codes containing model conceptions, which can accurately predict orifice flows, are essential. In an effort to provide usable further insight into flows across restrictors such as orifices this publication compares test results, CFD calculations and orifice loss calculation models from the open literature with the aid of transformation laws and contour plots. The influence of different geometric features is incorporated into a model for the calculation of discharge coefficients.

Experimental Study on Pressure Losses in Circular Orifices With Inlet Cross Flow

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Daniel Feseker ◽  
Mats Kinell ◽  
Matthias Neef
Keyword(s):  
Experimental Study ◽  
Film Cooling ◽  
Gas Turbines ◽  
Discharge Coefficient ◽  
Pressure Ratio ◽  
Cross Flow ◽  
Pressure Losses ◽  
Wide Range ◽  
Cooling Hole ◽  
Secondary Air

The ability to understand and predict the pressure losses of orifices is important in order to improve the air flow within the secondary air system. This experimental study investigates the behavior of the discharge coefficient for circular orifices with inlet cross flow which is a common flow case in gas turbines. Examples of this are at the inlet of a film cooling hole or the feeding of air to a blade through an orifice in a rotor disk. Measurements were conducted for a total number of 38 orifices, covering a wide range of length-to-diameter ratios, including short and long orifices with varying inlet geometries. Up to five different chamfer-to-diameter and radius-to-diameter ratios were tested per orifice length. Furthermore, the static pressure ratio across the orifice was varied between 1.05 and 1.6 for all examined orifices. The results of this comprehensive investigation demonstrate the beneficial influence of rounded inlet geometries and the ability to decrease pressure losses, which is especially true for higher cross flow ratios where the reduction of the pressure loss in comparison to sharp-edged holes can be as high as 54%. With some exceptions, the chamfered orifices show a similar behavior as the rounded ones but with generally lower discharge coefficients. Nevertheless, a chamfered inlet yields lower pressure losses than a sharp-edged inlet. The obtained experimental data were used to develop two correlations for the discharge coefficient as a function of geometrical as well as flow properties.

Experimental Study on Pressure Losses in Circular Orifices With Inlet Cross Flow

2017 ◽  
Author(s):  
Daniel Feseker ◽  
Mats Kinell ◽  
Matthias Neef
Keyword(s):  
Experimental Study ◽  
Film Cooling ◽  
Gas Turbines ◽  
Discharge Coefficient ◽  
Pressure Ratio ◽  
Cross Flow ◽  
Pressure Losses ◽  
Wide Range ◽  
Air System ◽  
Secondary Air

The cooling air in the secondary air system of gas turbines is controlled and metered by numerous restrictors, mainly in the shape of orifices. The ability to understand and predict the associated pressure losses are important in order to improve the air flow in the secondary air system. This experimental study investigates the behavior of the discharge coefficient for circular orifices with inlet cross flow which is a common flow case in gas turbines. Examples of this are at the inlet of a film cooling hole or the feeding of air to a blade through an orifice in a rotor disc. Measurements were conducted for a total number of 38 orifices, covering a wide range of length-to-diameter ratios, including short and long orifices with varying inlet geometries. Up to five different chamfer-to-diameter and radius-to-diameter ratios were tested per orifice length. Furthermore, the static pressure ratio across the orifice was varied between 1.05 and 1.6 for all examined orifices. The results of this comprehensive investigation demonstrate the beneficial influence of rounded inlet geometries and the ability to decrease pressure losses, which is especially true for higher cross flow ratios where the reduction of the pressure loss in comparison to sharp edged holes can be as high as 54%. With some exceptions, the chamfered orifices show a similar behavior as the rounded ones but with generally lower discharge coefficients. Nevertheless, a chamfered inlet yields lower pressure losses than a sharp edged inlet. The obtained experimental data was used to develop two correlations for the discharge coefficient as a function of geometrical as well as flow properties.

scholarly journals Discharge Coefficients of Ports with Stepped Inlets

Aerospace ◽  
2018 ◽  
Vol 5 (3) ◽  
pp. 97
Author(s):  
Adrian Spencer
Keyword(s):  
Gas Turbines ◽  
Discharge Coefficient ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Empirical Correlations ◽  
Equivalent Radius ◽  
One Dimensional ◽  
Vena Contracta ◽  
Discharge Coefficients ◽  
The Subject

Components of aeronautical gas turbines are increasingly being constructed from two layers, including a pressure containing skin, which is then protected by a thermal tile. Between them, pedestals and/or other heat transfer enhancing features are often employed. This results in air admission ports through the dual skin having a step feature at the inlet. Experimental data have been captured for stepped ports with a cross flow approach, which show a marked increase of 20% to 25% in discharge coefficient due to inlet step sizes typical of combustion chamber configurations. In this respect, the step behaves in a fashion comparable to ports with inlet chamfering or radiusing; the discharge coefficient is increased as a result of a reduction in the size of the vena contracta brought about by changes to the flow at inlet to the port. Radiused and chamfered ports have been the subject of previous studies, and empirical correlations exist to predict their discharge coefficient as used in many one-dimensional flow network tools. A method to predict the discharge coefficient change due to a step is suggested: converting the effect of the step into an equivalent radius to diameter ratio available in existing correlation approaches. An additional factor of eccentricity between the hole in the two skins is also considered. Eccentricity is shown to reduce discharge coefficient by up to 10% for some configurations, which is more pronounced at higher port mass flow ingestion fraction.

Investigation of the Prediction Correlations for the Flow Through Rotating Orifices in the Gas Turbine Secondary Air Flow System

2013 ◽  
Author(s):  
Deoras Prabhudharwadkar ◽  
Zain Dweik ◽  
A. Subramani ◽  
Murali Krishnan R.
Keyword(s):  
Gas Turbine ◽  
Discharge Coefficient ◽  
Flow System ◽  
Air Flow ◽  
Tangential Velocity ◽  
Cross Flow ◽  
Secondary System ◽  
Accurate Analysis ◽  
Secondary Air ◽  
Reliable Design

The secondary air flow system of a gas turbine cools and seals those parts of the turbine which would otherwise be exposed to the high temperatures, resulting in their life reduction or even failures. At the same time, excessive secondary air flow hinders the performance of the engine. Accurate analysis of the secondary system is therefore necessary to safeguard the reliable design of the engine and accurate life predictions. The secondary system is analyzed through the flow network analysis which comprises of chambers or cavities connected through flow passages or restrictions. There are significant number of locations where the air passes through stationary or rotating holes, e.g., the pre-swirl nozzles and the turbine blade receiver holes respectively. The accuracy of the flow prediction depends on the accuracy of the orifice discharge coefficient. This paper provides a detailed assessment of the available discharge coefficient correlations. The discharge coefficient has been found to be dependent on the geometric parameters (viz., length, inlet radius, chamfer), and the amount of cross-flow at the orifice entrance. The cross-flow may result from the relative tangential velocity between the orifice and the air or the inclination of the inlet flow with respect to the orifice axis. In this study, it was found that the discharge coefficient correlations provide similar predictions for flows without any cross-flow. However, significant deviations are seen in the predictions for the cases involving cross-flow. To identify the most accurate correlation for secondary flow application, a thorough assessment was performed using the static and the rotating test data available in the literature. In addition to the comparison using available experimental data, a CFD study was performed to independently assess the correlations. This exercise led to the identification of the most suitable correlation for our application.

Effect of Air-Curtains on Labyrinth Seal Performance

2016 ◽  
Author(s):  
Aakash C. Rai ◽  
Deoras Prabhudharwadkar ◽  
Sunil Murthy ◽  
Andrew Giametta ◽  
David Johns
Keyword(s):  
Gas Turbines ◽  
Cross Flow ◽  
Labyrinth Seal ◽  
Labyrinth Seals ◽  
Air Curtain ◽  
Baseline Design ◽  
Leakage Flows ◽  
Seal Design ◽  
Parametric Studies ◽  
Secondary Air

Labyrinth seals are used in many key sealing locations in gas turbines to control various leakage flows, e.g., to control the secondary air-flow from the compressor (bypassing the combustor), the turbine inter-stage leakages and blade tip leakages. This study was performed to assess the improvement in the performance of a labyrinth seal by using an air-curtain (cross-flow jet(s)) from the stator. Detailed parametric studies were performed to study the effect of the air-curtain jet pressure, location, and the number of jets on the seal performance with respect to the leakage flow. The analysis was done using 2-dimensional axisymmetric CFD simulations. It was found that in the case of a labyrinth seal with a flat stator (without a honeycomb attached to the stator) the air-curtain design can reduce the seal leakage by about 30% over the baseline seal design without air-curtains. This reduction happened because the air-curtain jet deflected the main seal jet away from the seal clearance. A similar conclusion was also obtained in case of a labyrinth seal with a honeycombed stator. Furthermore, our parametric studies with different air-curtain designs parameters implemented over a honeycombed labyrinth seal showed that the air-curtain jet pressure, location, and the number of jets were crucial factors governing the seal leakage. Amongst the air-curtain designs studied, it was found that implementing three air-curtains in the 1st pocket gave the maximum leakage reduction (by about 50%) over the baseline design.

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.

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

2014 ◽  
Vol 136 (8) ◽  
Author(s):  
Jan Sousek ◽  
Daniel Riedmüller ◽  
Michael Pfitzner
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Discharge Coefficient ◽  
Cross Flow ◽  
Test Rig ◽  
Flow Phenomena ◽  
Rotating Shafts ◽  
Discharge Behavior ◽  
Secondary Air ◽  
Cooling Air

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 since their aerodynamical behavior is different from that of axial or stationary holes due to the presence of centrifugal and Coriolis forces. A test rig containing two independently rotating shafts was designed in order to investigate the flow phenomena and the discharge behavior of these orifices. The required air mass flow is delivered by a screw compressor and can be independently regulated to supply the inner and outer annular passages of the test rig. It allows for 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 (nonrotating and rotating) on the discharge behavior of orifices in the outer shaft. To complement the data acquired from the experiments and to obtain a better understanding of the flow field near the rotating holes numerical flow simulations were also performed.

CFD Prediction of Secondary Airflow Through Holes in Rotating Shafts

2003 ◽  
Author(s):  
Colin Young ◽  
Guy D. Snowsill
Keyword(s):  
Gas Turbines ◽  
Flow Characteristics ◽  
Quantitative Information ◽  
Economic Incentives ◽  
Operating Conditions ◽  
System Component ◽  
Detailed Knowledge ◽  
Internal Cooling ◽  
Component Design ◽  
Secondary Air

Internal cooling of gas turbine engines is achieved by bleeding air off from various compressor stages and delivering it, via a complex network of flow passages, to the desired location. In modern gas turbines the air bled off for such purposes may account for up to 20% of the core airflow and is controlled by static and rotating restrictions such as orifices and seals. As this secondary air makes no direct contribution to engine thrust, there are strong economic incentives for acquiring a detailed knowledge of the flow characteristics of such devices under engine operating conditions, so that secondary air consumption can be minimised. In the present work the behaviour of secondary airflow through radial drillings in concentric shaft assemblies undergoing co- and contra-rotation is investigated using CFD techniques. The results of this work compare well with previously published orifice flow data and provide qualitative and quantitative information on these complex flows to support future air system component design.

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