Institut für Thermische Strömungsmaschinen. PDA Measurements of the Stationary Reacting Flow

Transcription

1 Institut für Thermische Strömungsmaschinen Dr.-Ing. Rainer Koch Dipl.-Ing. Tamas Laza DELIVERABLE D2.2 PDA Measurements of the Stationary Reacting Flow CONTRACT N : PROJECT N : ACRONYM: TITLE: TASK 2.1: SUBTASK 2.1.1: GR4D-CT GRD MUSCLES Modelling of Unsteady Combustion in Low Emssion Systems Prediction of lean blowout in liquid fueled combustion Investigation of the non-stationary two-phase flow at lean blowout University Karlsruhe (TH)

2 i Contents 1 Introduction Objectives of this subtask Focus of this deliverable report Test-Rig and Operating Conditions Atomizer Combustor Test Rig Operating Conditions Fuel Characteristics PDA Setup 5 4 PDA Results Measurement Locations PDA Data Sample Plots of the PDA Data Droplet Size Distribution Droplet Velocities Data Base File Organization

3 1 1 Introduction 1.1 Objectives of this subtask Goal of subtask Prediction of lean blowout in liquid fueled combustion is the experimental investigation of the unsteady two-phase flow in the presence of combustion oscillations. The experimental data will be used by other subtasks within work-package 2 Prediction of unsteady reacting flow and validation to verify and validate numerical methods for predicting two-phase flows under unsteady flow situations. This sub task is subdivided into two steps: 1. Investigation of the two-phase flow at lean blow off with stable flow 2. Investigation of the two-phase flow at lean blow off with unsteady flow For both operating conditions, the flow field as well as the two-phase flow are to be studied by LDA and PDPA. In case of unsteady flow, the analysis will also comprise phase-locked measurements. 1.2 Focus of this deliverable report The present deliverable report comprises the study of the stable reacting flow. Detailed data of the two-phase flow have been recorded by PDA. These data serve for validation of numerical codes. As prerequisite to the present deliverable, the the characteristics of the atomizer have been studied under non-reacting conditions and documented in deliverable report D2.1. The results of the experimental investigation of the unsteady reacting flow will be presented in a later deliverable report D2.3.

4 2 2 Test-Rig and Operating Conditions For the present subtask, an atomizer was selected which has been studied at the Institut für Thermische Strömungsmaschinen previously. Therefore, extensive knowledge of the atomizer characteristics under non-reacting and reacting conditions is available. The atomizer which will be described subsequently is to be used throughout the course of the project. 2.1 Atomizer A schematic of the atomizer is depicted in Fig.2.1. The atomizer is a pre-filmer design. It Primary air Secondary air 8 Atomizing edge Swirl generator Fig. 2.1: Schematic of the Atomizer consists of an hollow cone pressure atomizer located at the center. The cone angle of the spray is 8. The air is fed into the nozzle through 2 passages, both equipped with swirling vanes. The droplets produced by the hollow cone pressure atomizer are deposited on the pre-filming lip leading a build-up of liquid film. This film is driven by the primary air flow to the atomizing edge, where the final break up into droplet takes place. The secondary air flow is contra-rotating to the primary one, and assists the atomization of the liquid sheet. The swirl number the primary air is.45 and that of the secondary air.84.

5 Test-Rig and Operating Conditions Combustor The atomizer was mounted into a combustor with a cylindrical cross section. The inner diameter of the combustor is 5 mm. For optical access, the first section of the combustor consists either of a quartz glass tube or an metallic housing with plane windows (LDA, PDA). In Fig. 2.2 the combustor is shown with mounted quartz glass tube. A sketch of the combustor with the metallic housing with plane windows is shown in Fig Downstream the measurement section, the walls of the combustor are cooled by water. Fig. 2.2: Combustor with Quartz Glass Tube 2.3 Test Rig The combustor was integrated in an atmospheric test rig. The compressed air can be preheated by an electrical heater. A schematic of the rig is shown in Fig Fig. 2.3: Schematic of the Test Rig

6 4 Test-Rig and Operating Conditions 2.4 Operating Conditions The operating conditions for the present study have been set to an air mass flow which ensures proper stable operation under reacting conditions. An equivalence ratio of 2 was selected which is typical for the operation of modern lean premixed combustion systems. The air was preheated to 6 K. The air flow split between the two air passages of the nozzle was adjusted so that the pressure loss through the primary as well as the secondary air passage was 3 %. For this operating point, the ratio of the primary to the secondary air mass flow is 45/55. The details of the operating condition are listed in Tab Air Fuel! "#! $&%(')*+,.-/) 1 [g/s] [g/s] - - [K] [K] - [g/s] [K] / Table 2.1: Operating Conditions of the Atomizer 2.5 Fuel Characteristics For all runs of the present investigation Kerosine JET A-1 fuel from the same batch was used. The physical properties of the fuel have been determined by a detailed analysis. The data are summarized in Tab Density [kg/m2 ] Kin. Viskosity [mm3 /s] 1.7 Surface Tension [N/m].225 Net Calorific Value [MJ/kg] Table 2.2: Physical Properties of the Fuel From the data of the fuel the stochiometric air-fuel ratio was determined to be 4 45 )H,76 879;:=<?>;@A+BDC EGF 5 'IKJ (2.1) EGF

7 5 3 PDA Setup For the characterization of the atomizer, the droplet size and the droplet velocity have been measured by Phase Doppler Anemometry. The section of the combustor directly downstream of the nozzle was equipped with two flat quartz windows mounted at an angle of 45. The setup is shown in Fig A two component PDPA system (AEROMETRICS) was used in forward scattering mode. The sender as well as the receiver units of the PDPA have been mounted on a traversing frame, which can be moved in axial as well as in radial direction. Sender Detector Window Scattered light Laser beam Window Atomizer Cooling combuster wall Flow dierction Fig. 3.1: PDPA Setup Based on previous calculations of the gain curves for kerosine (Jet A-1) which has an refractive index of n=1.45 at 3 K and n=1.38 at the boiling point at atmospheric pressure, it was found that a detection angle of would be optimal. This detection angle will give the best dominance of the first order scattering mode. However, in order to have optical access to positions close to the wall of the combustor, large optical windows would be required for this detection angle, and an strong deviation from the round cross-section of the combustor had to be accepted. This would possibly impair the flow inside the combustor. As compromise, an angle of 45 between the windows was chosen.

8 6 4 PDA Results 4.1 Measurement Locations PDA measurements were performed a 9 planes downstream the nozzle. The axial positions are listed in Tab The first axial position was 6 mm, the last mm downstream the nozzle. Within each axial plane the distance between the radial positions was 1 mm or 2 mm. Axial Positions [mm] Table 4.1: Axial Measurement Positions for PDA In addition to the PDA measurements, the gas flow velocities have been studied by LDA at axial planes as shown in Tab The LDA measurements are not a required part of this deliverable report, but they are provided for completeness of the data base, in order to enable a comprehensive validation of two phase codes. For the LDA measurements, the velocities have Axial Positions [mm] Table 4.2: Axial Measurement Positions for LDA been recorded within each axial plane at radial positions starting at -5 mm and ending at 45 mm with a step width of 5 mm. 4.2 PDA Data The data recorded by the PDA have been processed and the characteristic droplet diameters and velocities were extracted for each measurement location. The droplet diameter distribution is characterized by,, and the Sauter mean diameter. From the measured 2 3 droplet velocities, the characteristic values of droplets with a diameter of 3,, have been extracted. 4.3 Sample Plots of the PDA Data In order to illustrate the results of the PDA measurements, subsequently some sample plots of the droplet size distributions and the droplet velocities are shown. At some location there was an insufficient data rate preventing to extract correct values. A typical example is the axial droplet velocity of the 3 droplets 6 mm downstream of the nozzle (Fig. 4.5). In those case the data have been set to zero.

9 PDA Results Droplet Size Distribution 8 Droplet Diameter [µ m] 7 3 z = 6 mm D D D9 D32 3 Fig. 4.1: Droplet size distribution 6 mm downstream the nozzle 8 Droplet Diameter [µ m] 7 3 z = mm D D D9 D32 3 Fig. 4.2: Droplet size distribution mm downstream the nozzle

10 8 PDA Results 8 Droplet Diameter [µ m] 7 3 z = mm D D D9 D32 3 Fig. 4.3: Droplet size distribution mm downstream the nozzle 8 Droplet Diameter [µ m] 7 3 z = mm D D D9 D32 3 Fig. 4.4: Droplet size distribution mm downstream the nozzle

11 PDA Results Droplet Velocities 7 Axial Velocity [m/s] 3 z = 6 mm No sufficient data rate Vaxial-D3 Vaxial-D Vaxial-D 3 Fig. 4.5: Droplet velocities 6 mm downstream the nozzle 7 Axial Velocity [m/s] 3 z = mm Vaxial-D3 Vaxial-D Vaxial-D 3 Fig. 4.6: Droplet velocities mm downstream the nozzle

12 PDA Results 7 Axial Velocity [m/s] 3 z = mm Vaxial-D3 Vaxial-D Vaxial-D 3 Fig. 4.7: Droplet velocities mm downstream the nozzle 7 Axial Velocity [m/s] 3 z = mm Vaxial-D3 Vaxial-D Vaxial-D 3 Fig. 4.8: Droplet velocities mm downstream the nozzle

13 11 5 Data Base 5.1 File Organization The complete data set of the PDA measurements are provided on an attached CD-ROM. The files are organized as follows: Main directory: Deliverable-2.2.pdf: This deliverable report. Directory PDA: pda_diameter.dat: Data file with droplet diameters from PDA measurements. pda_velocities.dat: Data file with droplet velocities from PDA measurements. Directory LDA: lda_velocities.dat: Data file with air flow velocities from LDA measurements. All data files are in plain ASCII and arranged according to the TECPLOT format. The file pda_diameter.dat contains the data for,, and the Sauter mean diameter. The data file is subdivided into 9 zones representing the different axial positions 2 3 (6, 8,, 12.5, 15,, 3,, mm) downstream the nozzle. Within each zone, the data are provided as function of the radial coordinate (in mm), with r= representing the center axis. The file pda_velocities.dat is organized similarly as pda_diameter.dat. It contains also 9 zones representing the same axial positions. Within each zone, there are data of the radial, circumferential and axial velocity of droplets with a characteristic diameter of 3,, as function of the radial coordinate. The file lda_velocities.dat contains the air flow velocities from LDA measurements. It is a 2-D TECPLOT formatted file where the data are given as function of axial (z) and radial (r) coordinate (in mm). Provided are the axial velocity u, its RMS value u and the percentage of its turbulent fluctuation u. Similarly, the value of the circumferential velocity v are given.