Guido Stockhausen

Combined PIV and DGV applied to a pressurized gas turbine combustion facility

This paper provides an overview of flow field measurements on a pressurized generic combustor that shares typical features of realistic gas turbine combustors. Both Doppler global velocimetry (DGV) and particle image velocimetry (PIV) were applied in parallel to achieve volumetric, three-component velocity data sets of the reacting flow field at pressures of 2 and 10 bar with 700 K pre-heating. Limited optical access to the mixing zone required a combination of PIV and DGV to obtain averaged three-component velocity data from a single viewing direction. The acquired volume data sets of the time-averaged flow in the mixing zone contain about 40 parallel planes spaced at 2 mm with a spatial resolution of 1.2 × 1.2 mm2 each. Difficulties encountered in the application of stereoscopic PIV to a simple atmospheric generic combustor illustrate the advantage of the combined PIV–DGV technique.

Performance and accuracy investigations of two Doppler global velocimetry systems applied in parallel

Two Doppler global velocimetry systems were applied in parallel to assess their performance in wind tunnel environments. Both DGV systems were mounted on a common traverse surrounding the glass- walled 1.4×1.8 m 2 test section of the wind tunnel. The traverse normally supports a three-component forward-scatter laser Doppler velocimetry system. The reproducible vortical flow field generated by the blunt tip of an airfoil was chosen for this investigation and was precisely surveyed by LDA just prior to the DGV measurements. Both DGV systems shared the same continuous wave laser light source, laser frequency stabilization and fiber optic light sheet delivery system. The principle differences between the DGV implementations are with regard to the imaging configuration. One configuration relied on a single camera that observed three successively operated light sheets. In the second configuration, three camera views simultaneously observed a single light sheet using a four-branch fiber imaging bundle. The imaging bundle system had all three view points in a forward scattering arrangement which increased the scattering efficiency but reduced the frequency shift sensitivity. Since all three light sheet observation components were acquired onto the same image frame, acquisition times could be reduced to a minimum. On the other hand, the triple light sheet − single camera system observed two light sheets in forward scatter and one light sheet in backscatter. Although three separate images had to be recorded in succession, the image quality, spatial resolution and signal-to-noise ratio was superior to the imaging bundle system. Comparison of the DGV data with LDV measurements shows very good agreement to within 1-2 m/s. The remaining discrepancy has a variety of causes, some are related to the reduced resolving power of the fiber imaging bundle system (graininess, smoothing), exact localization of the receiver head with respect to the scene, laser frequency drift or background influences. The extensive data base available allows a more detailed study of the influences of each of these factors.

Selected applications of planar imaging velocimetry in combustion test facilities

This chapter provides an overview on the application of particle image velocimetry (PIV) and Doppler global velocimetry (DGV) in combustion test facilities that are operated at pressures of up to 10 bar. Emphasis is placed on the experimental aspects of each application rather than the interpretation of the acquired flow-field data because many of the encountered problems and chosen solution strategies are unique to this area of velocimetry application. In particular, imaging configurations, seeding techniques, data-acquisition strategies as well as pre- and postprocessing methodologies are outlined.

On the development of Doppler global velocimetry for cryogenic wind tunnels

A specially designed Doppler global velocimetry system (DGV, planar Doppler velocimetry) was tested in a high-speed cryogenic facility at Mach 0.3 to Mach 0.8 and pressures between 1.2 and 2.5 bar. The necessary seeding was achieved by injecting a mixture of gaseous nitrogen and water vapor into the dry and cold tunnel flow which then immediately formed a large amount of small ice crystals. As operational and access conditions are quite restrictive with respect to other facilities, DGV is currently considered the best choice for the non-intrusive measurement of flow fields. A comparison of DGV to the more wide-spread particle image velocimetry technique (PIV) is also given.

Methods to improve pressure, temperature and velocity accuracies of filtered Rayleigh scattering measurements in gaseous flows

Frequency scanning filtered Rayleigh scattering is able to simultaneously provide time-averaged measurements of pressure, temperature and velocity in gaseous flows. By extending the underlying mathematical model, a robust alternative to existing approaches is introduced. Present and proposed model functions are then characterized during a detailed uncertainty analysis. Deviations between the analytical solution of a jet flow experiment and measured results could be related to laser-induced background radiation as well as the Rayleigh scattering’s spectral distribution. In applying a background correction method and by replacing the standard lineshape model by an empirical formulation, detrimental effects on pressure, temperature and velocity accuracies could be reduced below 15 hPa, 2.5 K and 2.7 m/s.

Nonintrusive Flowfield, Temperature and Species Measurements on a Generic Aeroengine Combustor at Elevated Pressures

A generic combustor was built, that gives wide optical access at higher pressure and shares typical features with aero engine combustors. A comprehensive data set for validation of RANS and LES codes was generated at isothermal as well as combusting conditions at 2 and 10 bars with 650 K preheat using natural gas as fuel. The velocity field was measured using LDA (Laser Doppler Anemometry) and DGV (Doppler Global Velocimetry) as well as PIV (Particle Image Velocimetry). Temperature data were acquired using CARS (Coherent Anti stokes Raman Scattering) and SRS (Spontaneous Raman Scattering). Major species concentrations as well as the mixture fraction in the primary zone of the combustor were also measured using SRS. Mean and RMS values of the temperature measured by CARS in the secondary zone illustrate the influence of the jet impingement on the unsteady mixing of the jets with the swirling primary air. [Keywords: non intrusive measurements, aero engine combustion, elevated pressure]

Temperature Measurements at the Outlet of a Lean Burn Single Sector Combustor by Laser-Optical Methods

High OPR engine cycles for reduced NOx emissions will generate new aggravated requirements and boundary conditions by implementing low emission combustion technologies into advanced engine architectures. Lean burn combustion systems will have a significant impact on the temperature and velocity traverse at the combustor exit. The highly swirling flow from the lean burn fuel injector interacts with the combustor wall cooling before exiting the combustor. As a large portion (up to 80%) of the total flow passes through the fuel injector, the combustor exit flow and temperature field is dominated by the fuel injector. With the transition to high pressure engines it is essential to fully understand and determine the high energetic interface between combustor and turbine to avoid excessive cooling with detrimental impacts to turbine and overall engine efficiency. In this context the knowledge of temperature distributions at the combustor exit is of special importance. A lean burn single sector combustor was designed and built at DLR, providing optical access to the exit section. The sector was operated with a staged lean burn injector from Rolls-Royce Deutschland. Spatially resolved temperatures were measured at different operating conditions using planar laser-induced fluorescence of OH (OH-PLIF) and Filtered Rayleigh Scattering (FRS), the latter being used in a combustor environment for the first time. Apart from a conventional signal detection arrangement, FRS was also applied with an endoscope for signal collection, to assess its feasibility for future application in a full annular combustor with restricted optical access. Both techniques are complementary in several respects, which justified their combined application and comparative assessment in this specific environment. OH-PLIF allows instantaneous measurements and therefore enables local temperature statistics, but is limited to relatively high temperatures. On the other hand FRS can also be applied at low temperatures, which makes it particularly attractive for measurements in cooling layers. However, due to the weak physical process of Rayleigh scattering, FRS requires long sampling times and therefore can only provide temporal averages. When applied in combination, the accuracy of both techniques could be improved by each method helping to overcome the other’s shortcomings. In an accompanying paper, additional experiments are described which characterize the flow field at the combustor exit; the combined data provide comprehensive information on combustor exit conditions.

Flow Field Characterization at the Outlet of a Lean Burn Single Sector Combustor by Laser-Optical Methods

High OPR engine cycles for reduced NOx emissions will generate new aggravated requirements and boundary conditions by implementing low emission combustion technologies into advanced engine architectures. Lean burn combustion systems will have a significant impact on the temperature and velocity traverse at the combustor exit. Lean burn fuel injectors dominate the combustor exit conditions. This is due to the fact that they pass a majority of the total combustor flow, and to the lack of mixing jets like in a conventional combustor. With the transition to high pressure engines it is essential to fully understand and determine the high energetic interface between combustor and turbine to avoid excessive cooling, which has a detrimental impact on turbine and overall engine efficiency. Velocity distributions and their fluctuations at the combustor exit for lean burn are of special interest as they can influence the efficiency and capacity of the turbine. Within the EU project LEMCOTEC, a lean burn single sector combustor was designed and built at DLR, providing optical access to its rectangular exit section. The sector was operated with a fuel staged lean burn injector from Rolls-Royce Deutschland. Measurements were performed under various operating conditions, covering idle and cruise operation. Two techniques were used to perform velocity measurements at the combustor exit in the demanding environment of highly luminous flames under elevated pressures: Particle Image Velocimetry (PIV) and Filtered Rayleigh Scattering (FRS).The latter was used for the first time in an aero-engine combustor environment. In addition to a conventional signal detection arrangement, FRS was also applied with an endoscope for signal collection, to assess its practicality for a potential future application in a full annular combustor with restricted optical access. Both measurement techniques are complementary in several respects, which justified their respective application and comparative assessment. PIV is able to record instantaneous velocity distributions and is therefore capable to deliver higher velocity moments, in addition to temporal averages. Applied in two orthogonal traversable light sheet arrangements, it could be used to map all three velocity components across the entire combustor cross section, and obtain data on velocity variances, cross-correlations and turbulence intensities. FRS is limited to measurements of average velocities, as long sampling times are required due to the weak physical process of Rayleigh scattering. However, FRS has two advantages: It requires no particle seeding, because it is based on the measurement of a molecular Doppler shift, and it can provide temperature information simultaneously. This contribution complements a second paper (GT2016-56370) focusing on the measurement of temperature distributions at the same combustor exit section by laser-based optical methods.

Pressure, temperature and three-component-velocity fields by filtered Rayleigh scattering velocimetry

The filtered Rayleigh scattering (FRS) technique, extended by the method of frequency scanning, is a powerful tool to characterize thermodynamic, as well as aerodynamic, properties of technical flows. In this Letter, we report on the first application of an FRS velocimeter, which is capable of acquiring time-averaged planar pressure, temperature, and three-component velocity distributions simultaneously. The method is validated by characterizing the near-field, as well as the far-field, of a turbulent jet.

Application of Endoscopic OH*-Chemiluminescence Measurements at a Full-Scale High-Pressure Gas Turbine Combustion Test Rig

Single burner combustion tests play a key role in the Siemens gas turbine combustion system development process. The main scope of these tests is to assess the performance of combustor design variants in terms emissions or combustion stability at gas turbine relevant operation conditions. Both emissions and combustion stability strongly depend on the flame front and flame position. A pragmatic approach to investigate the flame is to detect the chemiluminescence signal of the combustion intermediate species OH*. Thus, the OH*-chemiluminescence signal was recorded at high-pressure combustion tests to get more insight in the complex interactions between combustor design, operation conditions and combustion performance.To minimize the impact of the measurement system on the combustion behavior, the optical access to the test rig was realized by using a water-cooled probe with an UV-transparent endoscope. The probe was located in the test rig side-wall, downstream of the burner outlet, viewing towards the burner with a 90° angle relative to the endoscope orientation. The experimental setup was completed by a combination of bandpass filters and an ICCD camera.During the experiments acoustic pressure oscillations inside the combustion chamber were recorded simultaneously to the chemiluminescence images to allow for phase-sorting of the recorded images during the image post-processing. The post-processed images then were correlated with the pressure oscillations to investigate the relationship of the heat release to the pressure oscillations.The measurements were carried out during single burner gas turbine combustion tests at realistic gas turbine operation conditions at a scaled pressure of 9 bar.This paper presents selected test results and discusses how they give new insight in the complex combustion processes at full-scale high-pressure gas turbine combustion tests.Copyright