The effect of density differences on the path of jets

1961 ◽  
Vol 263 (1314) ◽  
pp. 340-352 ◽  
Keyword(s):  
Density Ratio ◽  
Operating Conditions ◽  
Turbulent Jet ◽  
Water Model ◽  
Hot Gas ◽  
Gas Jets ◽  
Air Jets ◽  
Buoyancy Forces ◽  
Secondary Air ◽  
Model Technique

A turbulent jet of fluid injected into surroundings of different density, soon diverges from its axis of projection as a result of gravitational or buoyancy forces. This feature is exhibited by hot gas jets, in particular by flames, preheated secondary air jets, and effluent plumes. In this paper a water-model technique is described which has been devised to represent the path taken by such jets. This consists of a large transparent box through which a slow stream of water flows and into which a jet of magnetite slurry is injected, to be photographed against an illuminated background. In the model the jet density is greater than that of the surroundings, but the results apply equally to the case where the density ratio is reversed, by considering the trajectory to be inverted. A method of predicting the axes of the heterogeneous jet systems in terms of the initial velocity, the density ratio, the nozzle diameter and the angle of inclination of the axis of projection, is presented. Predicted axes for a variety of operating conditions are shown to compare favourably with observed values obtained in the water model.

Experimental and Numerical Investigation of a Planar Combustor Sector at Realistic Operating Conditions

2000 ◽  
Vol 123 (4) ◽  
pp. 810-816 ◽  
Author(s):  
M. Carl ◽  
T. Behrendt ◽  
C. Fleing ◽  
M. Frodermann ◽  
J. Heinze ◽  
...  
Keyword(s):  
Reduction Potential ◽  
Measurement Techniques ◽  
Nox Reduction ◽  
Mie Scattering ◽  
Isothermal Flow ◽  
Operating Conditions ◽  
Aerospace Research ◽  
Air Jets ◽  
Secondary Air ◽  
German Aerospace

Results of an ongoing collaboration between the engine manufacturer MTU and the German aerospace research center DLR on the NOx reduction potential of conventional combustors are reported. A program comprising optical sector combustor measurements at 1, 6, and 15 bars and CFD calculations is carried out. The aims are to gather information in the combustor at realistic operating conditions, to understand the differences between the sector flow field and data from tubular combustors, to verify the used CFD, and to discover the benefits and limitations of the applied optical diagnostics. Selected results of measurements and calculations of the isothermal flow and of measurements at 6 bars and 700 K at a rich-lean and overall lean AFR are reported. The used measurement techniques were LDA, PDA, Mie scattering on kerosene, quantitative light scattering, OH* chemiluminescence, and LIF on OH. The measurements were able to confirm the intended quick and homogeneous mixing of the three staggered rows of secondary air jets.

1D Tool for Stator-Rotor Cavities Integrated Into a Fluid Network Solver of Heavy-Duty Gas Turbine Secondary Air System

2010 ◽  
Author(s):  
F. Bonzani ◽  
L. Bozzi ◽  
M. Mantero ◽  
A. Vinci ◽  
L. Innocenti ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Heavy Duty ◽  
Ambient Conditions ◽  
Hot Gas ◽  
Fluid Network ◽  
Air System ◽  
Air Flows ◽  
Secondary Air

In order to improve performance of heavy-duty gas turbines, in terms of efficiency and reliability, accurate calculation tools are required to simulate the SAS (Secondary Air System) and estimate the minimum amount of cooling and sealing air to ensure the integrity of hot gas path components. A critical component of this system is the cavity formed between coaxial rotating and stationary discs, that needs a sealing flow to prevent the hot gas ingestion. This paper gives a general overview of a 1D tool for the analysis of stator-rotor cavities and its integration into an “in-house” developed fluid network solver to analyse the behaviour of the secondary air system over different operating conditions. The 1D cavity solver calculates swirl, pressure and temperature profiles along the cavity radius. Thanks to its integration into the SAS code, the cavity solver allows estimation of sealing air flows, taking into account directly of the interaction between inner and outer extraction lines of blades and vanes. This procedure has been applied to the AE94.3A secondary air system and the results are presented in terms of sealing flows variation for the cavities of second and third vane on gas turbine load and ambient conditions. In some different load conditions, calculated secondary air flows are compared to experimental data coming from the AE94.3A Ansaldo fleet.

Experimental and Numerical Investigation of a Planar Combustor Sector at Realistic Operating Conditions

2000 ◽  
Author(s):  
Thomas Behrendt ◽  
Martin Carl ◽  
Christian Fleing ◽  
Matthias Frodermann ◽  
Johannes Heinze ◽  
...  
Keyword(s):  
Reduction Potential ◽  
Measurement Techniques ◽  
Nox Reduction ◽  
Mie Scattering ◽  
Isothermal Flow ◽  
Operating Conditions ◽  
Aerospace Research ◽  
Air Jets ◽  
Secondary Air ◽  
German Aerospace

Results of an ongoing collaboration between the engine manufacturer MTU and the German aerospace research center DLR on the NOx reduction potential of conventional combustors are reported. A program comprising optical sector combustor measurements at 1, 6 and 15 bars and CFD calculations is carried out. The aims are to gather information in the combustor at realistic operating conditions, to understand the differences between the sector flow field and data from tubular combustors, to verify the used CFD and to discover the benefits and limitations of the applied optical diagnostics. Selected results of measurement and calculation of the isothermal flow and of measurements at 6 bars and 700 K at a rich-lean and overall lean AFR are reported. The used measurement techniques were LDA, PDA, Mie scattering on kerosene, Quantitative Light Scattering, OH* Chemiluminescence and LIF on OH. The measurements were able to confirm the intended quick and homogeneous mixing of the three staggered rows of secondary air jets.

Effect of Periodic Wake Passing on Film Effectiveness of Discrete Cooling Holes Around the Leading Edge of a Blunt Body

1997 ◽  
Vol 119 (2) ◽  
pp. 292-301 ◽  
Author(s):  
K. Funazaki ◽  
M. Yokota ◽  
S. Yamawaki
Keyword(s):  
Blunt Body ◽  
Free Stream ◽  
Turbine Blades ◽  
Density Ratio ◽  
Leading Edge ◽  
Test Model ◽  
Free Stream Turbulence ◽  
Aero Engine ◽  
Secondary Air ◽  
Wake Passing

Detailed studies are conducted on film effectiveness of discrete cooling holes around the leading edge of a blunt body that is subjected to periodically incoming wakes as well as free-stream turbulence with various levels of intensity. The cooling holes have a configuration similar to that of typical turbine blades except for the spanwise inclination angle. Secondary air is heated so that the temperature difference between the mainstream and secondary air is about 20 K. In this case, the air density ratio of the mainstream and secondary air becomes less than unity, therefore the flow condition encountered in an actual aero-engine cannot be simulated in terms of the density ratio. A spoke-wheel type wake generator is used in this study. In addition, three types of turbulence grids are used to elevate the free-stream turbulence intensity. We adopt three blowing ratios of the secondary air to the mainstream. For each of the blowing ratios, wall temperatures around the surface of the test model are measured by thermocouples situated inside the model. The temperature is visualized using liquid crystals in order to obtain qualitative information of film effectiveness distribution.

The Effect of Periodic Wake Passing on Film Effectiveness of Discrete Cooling Holes Around the Leading Edge of a Blunt Body

1995 ◽  
Author(s):  
K. Funazaki ◽  
M. Yokota ◽  
S. Yamawaki
Keyword(s):  
Blunt Body ◽  
Free Stream ◽  
Turbine Blades ◽  
Density Ratio ◽  
Leading Edge ◽  
Test Model ◽  
Free Stream Turbulence ◽  
Aero Engine ◽  
Secondary Air ◽  
Wake Passing

Detailed studies are conducted on film effectiveness of discrete cooling holes around the leading edge of a blunt body that is subjected to periodically incoming wakes as well as free-stream turbulence with various levels of intensity. The cooling holes have a configuration similar to that of typical turbine blades except for the spanwise inclination angle. Secondary air is heated so that the temperature difference between the mainstream and secondary air is about 20K. In this case, air density ratio of the mainstream and secondary air becomes less than unity, therefore the flow condition encountered in an actual aero-engine can not be simulated in terms of the density ratio. A spoke-wheel type wake generator is used in this study. In addition, three types of turbulence grids are used to elevate the free-stream turbulence intensity. We adopt three blowing ratios of the secondary air to the mainstream. For each of the blowing ratios, wall temperature around the surface of the test model are measured by thermocouples situated inside the model. The temperature is visualized using liquid crystals in order to obtain qualitative information of film effectiveness distribution.

Secondary Air Systems in Aeroengines Employing Vortex Reducers

2001 ◽  
Author(s):  
Dimitrie Negulescu ◽  
Michael Pfitzner
Keyword(s):  
Flow Path ◽  
Supporting Evidence ◽  
Excessive Pressure ◽  
Pressure Losses ◽  
Low Pressure Turbine ◽  
Hot Gas ◽  
Air System ◽  
High Integrity ◽  
Secondary Air ◽  
Aero Engines

A secondary air system in modern aero engines is required to cool the compressor and turbine discs and make sure that no hot gas ingestion occurs into the cavities between the turbine discs, which could cause an inadvertent reduction of disc life. A high integrity solution for guiding the air from the compressor to the turbine is through an inner bleed from the compressor platform and through the space between the disc bores and the shaft connecting the fan with the low pressure turbine. Since strongly swirling air is taken from the compressor platforms to a much lower radius, a means of deswirling the air has to be used to avoid excessive pressure losses along the flow path. The paper describes a system utilizing tubeless vortex reducers to accomplish this deswirl, which are compared to a more conventional air system utilizing tubes. The working principles of both types of vortex reducer and guidelines for the design of a secondary air system using vortex reducers are explained with supporting evidence from rig tests and CFD calculations. Opportunities for the aerodynamic optimisation of the tubeless vortex reducer are elaborated and the experience gained using the system during the development of the BR700 engine is described.

Interactions of Film Cooling Rows: Effects of Hole Geometry and Row Spacing on the Cooling Performance Downstream of the Second Row of Holes

2003 ◽  
Author(s):  
Christian Saumweber ◽  
Achmed Schulz
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Large Scale ◽  
Density Ratio ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Staggered Arrangement ◽  
Film Cooling Holes

A comprehensive set of generic experiments is conducted to investigate the interaction of film cooling rows. Five different film cooling configurations are considered on a large scale basis each consisting of two rows of film cooling holes in staggered arrangement. The hole pitch to diameter ratio within each row is kept constant at P/D = 4. The spacing between the rows is either x/D = 10, 20, or 30. Fanshaped holes or simple cylindrical holes with an inclination angle of 30 deg. and a hole length of 6 hole diameters are used. With a hot gas Mach number of Mam = 0.3, an engine like density ratio of ρc/ρm = 1.75, and a freestream turbulence intensity of Tu = 5.1% are established. Operating conditions are varied in terms of blowing ratio for the upstream and, independently, the downstream row in the range 0.5<M<2.0. The results illustrate the importance of considering ejection into an already film cooled boundary layer. Adiabatic film cooling effectiveness and heat transfer coefficients are significantly increased. The decay of effectiveness with streamwise distance is much less pronounced downstream of the second row primarily due to pre-cooling of the boundary layer by the first row of holes. Additionally, a comparison of measured effectiveness data with predictions according to the widely used superposition model of Sellers [11] is given for two rows of fanshaped holes.

Influence of Flow Structure on Shaped Hole Film Cooling Performance

2010 ◽  
Author(s):  
Benoit Laveau ◽  
Reza S. Abhari
Keyword(s):  
Flow Structure ◽  
Thermal Performance ◽  
Turbine Blades ◽  
Density Ratio ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Infrared Measurements ◽  
Cylindrical Holes ◽  
Shaped Hole ◽  
Adiabatic Effectiveness

Shaped holes are used on modern turbine blades for their higher performance and greater lateral coolant spreading compared to classic streamwise angled holes. This study incorporates measurements and observations from a shaped hole geometry undertaken at ETH Zurich in which a row of laterally expanded diffusely shaped holes is compared to the classic row of streamwise round holes. Infrared measurements provide high-resolution data of the adiabatic effectiveness and three dimensional velocity measurements are carried out through stereoscopic Particle Image Velocimetry. Both experiments are run for similar operating conditions allowing a comparison to be made between the flow structure and the thermal performance. The adiabatic effectiveness is seen to be higher for shaped holes compared to cylindrical holes: in particular the laterally averaged values are higher due to a larger lateral spreading of the coolant. The work presented here shows the first results on the limited influence of the density ratio on the thermal performance. The performance is also influenced by the vortical structure. The typical counter-rotating vortex pair which is completed by another pair of anti-kidney vortices is observed with their strength being clearly reduced compared to the example with cylindrical holes. The doubled structure and the reduced strength change the behavior of the jet, explaining the higher performance of a jet with shaped holes. The vertical motion leading to lift-off is reduced, so the jet remains close to the surface even at high blowing rates. The goal of this article is to present data for the thermal performance and flow field of shaped holes and then explain the relationship between the two.

Modelling of Thermoacoustic Combustion Instabilities Phenomena: Application to an Experimental Rig for Testing Full Scale Burners

2014 ◽  
Author(s):  
Davide Laera ◽  
Giovanni Campa ◽  
Sergio M. Camporeale ◽  
Edoardo Bertolotto ◽  
Sergio Rizzo ◽  
...  
Keyword(s):  
Acoustic Analysis ◽  
Fem Analysis ◽  
Full Scale ◽  
Operating Conditions ◽  
System Modelling ◽  
Combustion Instabilities ◽  
Test Rig ◽  
Pressure Oscillations ◽  
Secondary Air ◽  
Actual Geometry

This paper concerns the acoustic analysis of self–sustained thermoacoustic pressure oscillations that occur in a test rig equipped with full scale lean premixed burner. The experimental work is conducted by Ansaldo Energia and CCA (Centro Combustione Ambiente) at the Ansaldo Caldaie facility in Gioia del Colle (Italy), in cooperation with Politecnico di Bari. The test rig is characterized by a longitudinal development with two acoustic volumes, plenum and combustion chamber, coupled by the burner. The length of both chambers can be varied with continuity in order to obtain instability at different frequencies. A previously developed three dimensional finite element code has been applied to carry out the linear stability analysis of the system, modelling the thermoacoustic combustion instabilities through the Helmholtz equation under the hypothesis of low Mach approximation. The heat release fluctuations are modelled according to the κ-τ approach. The burner, characterized by two conduits for primary and secondary air, is simulated by means of both a FEM analysis and a Burner Transfer Matrix (BTM) method in order to examine the influence of details of its actual geometry. Different operating conditions, in which self–sustained pressure oscillations have been observed, are examined. Frequencies and growth rates of unstable modes are identified, with good agreement with experimental data in terms of frequencies and acoustics pressure wave profiles.

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