Experiments on Thermal Fluid-Structure Interaction of a Cooling Channel Configuration

Transcription

1 Sonderforschungsbereich/Transregio 40 Annual Report Experiments on Thermal Fluid-Structure Interaction of a Cooling Channel Configuration By D. Daub, S. Willems, B. Esser AND A. Gülhan German Aerospace Center (DLR), Institute of Aerodynamics and Flow Technology, Supersonic and Hypersonic Technology Department, Linder Höhe, Köln Rocket engine components like combustion chambers and nozzles have to withstand severe aerothermal loads. Any failure will most likely cause the loss of the mission. To date the mechanisms leading to the failure of cooling channels in these components are not sufficiently understood. To contribute to the study of this fluid-structure coupled problem, a generic experimental setup with several cooling channels was designed and tested in the arc-heated wind tunnel L3K at DLR, Cologne. The model was instrumented with thermocouples to measure the internal temperature distribution. An infrared camera was used to monitor the surface temperature. After the wind tunnel runs, the hot gas wall of the cooling channels was checked for deformation. 1. Preliminary Remarks on Aeroelastic Fluid-Structure Interaction In addition to the thermal fluid-structure interaction experiments, further work was conducted regarding the study of aeroelastic fluid-structure interaction. It was shown in [1], that the structural model of the elastic panel used by D4 for the coupled simulation did not reproduce the behavior of the panel with the desired accuracy. Work regarding the modeling of the elastic panel is presented together with D4 in the report by Hammerl et al. [2] including reference experiments and a discussion of their implications for the modeling of the boundary conditions of the elastic panel. 2. Introduction 2.1. Relevance of Thermal Fluid-Structure Interaction for Future Launchers Rocket engine components have to withstand severe aerothermal loads caused by the hot combustion gases with temperatures up to 3500K, heat fluxes of 80MW/m 2 can be reached. A structural failure will most likely cause the loss of the mission [3]. To date the mechanisms leading to the failure of cooling channels in these components are not sufficiently understood, but understanding and correctly modeling such coupled problems is crucial for the design of future launchers. Therefore such problems are treated numerically [4], [5] and experimentally ( [6] and present study) within SBF/TRR Experiment Design For the present experimental study, the arc-heated wind tunnel L3K (Fig.1) [7] at DLR, Cologne was used. To obtain the maximum heat load and a homogeneous heat flux distribution on the cooled surface, the model is inserted perpendicularly into the flow

2 264 D. Daub, S. Willems, A. Gülhan & B. Esser FIGURE 1. Arc-heated wind tunnel L3K at DLR, Cologne FIGURE 2. Model in L3K test section (Fig.2). Therefore, the test article has to be sufficiently small posing several challenges for construction and instrumentation for the model. The model is only accessible from the back side and has to be supplied with coolant as well as instrumented with thermocouples.

3 Thermal Fluid-Structure Interaction of a Cooling Channel Configuration 265 (a) Cooling channel cross section (b) Access for thermocouples FIGURE 3. CT images Y Z X FIGURE 4. Thermocouple positions 3. Experimental Setup 3.1. Cooling System The model (Fig. 3) is supplied with water cooling for the frame and gaseous nitrogen for the central cooling channels. The water cooling channels are used to ensure the integrity of the frame surrounding the nitrogen cooling channels by keeping the frame area at low temperature while still allowing to reach high temperatures in the center of the front surface. Thus, known mechanical and thermal lateral boundary conditions are established. The nitrogen cooling channels are the subject of the investigation. There are five channels with a cross section of 14.5 Ü5.3mm, the thickness of the hot wall towards the oncoming flow is0.5mm.the thickness of the sidewalls between the cooling channels is 1mm. The cooling channels are machined from a block of CuCr1Zr (hot wall and side walls). The back side is closed by a galvanic process using Copper. The nitrogen mass flow was set to 7g/s using a Bronkhorst Coriflow mass flow controller.

4 266 D. Daub, S. Willems, A. Gülhan & B. Esser Ì ÖÑÓÓÙÔÐ ÔØ ÖÓÑ ÓØ Û ÐÐ mm Ì ½ 0.5 Ì ¾ 0.5 Ì 7.8 Ì 0.5 Ì 15.0 Ì 0.5 Ì 0.5 Ì 4.1 Ì 11.4 Ì ½¼ 0.5 TABLE 1. Installation depths of the thermocouples (a) Before mounting (b) Mounted FIGURE 5. Spring-mounted thermocouples Thermocouples 3.2. Instrumentation Type K class 1 thermocouples with a diameter of 0.25mm are used and mounted at various depths and locations. In the center of the test article, the thermocouples are mounted such that the extraction of a temperature profile in Z-direction (normal to the surface) is possible (Fig.4). Installation depths of the thermocouples are given in Table 1. The coolant supply and return at the model are also equipped with thermocouples. The thermocouples are mounted using springs to ensure good thermal contact with the model (Fig.5) Infrared Camera The infrared camera used is a Flir Thermavision 570 working at µm and a sensor resolution of 320 Ü 240 pixel Deformation Measurements Deformation is measured using a coordinate measuring machine Zeiss Prismo MP5 with a uncertainty smaller than 3µm. For the measurement, the model has to be removed from the wind tunnel.

5 Thermal Fluid-Structure Interaction of a Cooling Channel Configuration 267 ÐÓÛ È Ö Ñ Ø Ö Î Ö Ð Î ÐÙ ÐÓÛ ÓÑÔÓ Ø ÓÒ ËÔ Å Ö Ø ÓÒ Ma 7.6 N p 49Pa O T 541K NO v 3976m/s N O TABLE 2. Flow conditions Run 1 Run 2 Run TC 10 TC 6 TC 4 TC 7 TC 2 TC 1 Temperature 1/ C Temperature 1/ C Time 1/s (a) TC 4 at 0.5mm from hot surface Time 1/s (b) 0.5mm from hot surface - run mm 4.1 mm TC 4 TC 8 TC 3 TC 9 TC Temperature 1/ C mm 11.4 mm 15.0 mm Temperature 1/ C Time 1/s (c) Model temperature - run Z 1/mm (d) Temperature profile at center - run 3 FIGURE 6. Temperature distribution inside the model 3.3. Flow Conditions The flow conditions are given in table 2. They are similar to the flow conditions used for the experiments on flat and curved CMC plates in the previous funding period [8] and were obtained from a computation with the DLR TAU-code assuming laminar, non-

6 268 D. Daub, S. Willems, A. Gülhan & B. Esser FIGURE 7. Damaged nitrogen supply equilibrium air flow with 5 species. For the experiments presented here, the model was positioned 350mm downstream of the nozzle exit to obtain low heat loads for the first runs. 4. Experimental Results 4.1. Internal Temperature Figure 6(a) shows the temperature reading from three wind tunnel runs in the center of the model at a distance of 0.5mm from the hot surface. During run 2, an anomaly occurred. The heating process was slower and a higher temperature was reached. A failure of the nitrogen supply was found after the test (see Fig 7) caused by the hot flow surrounding the model. The temperature close to the surface was about 20 K higher at the locations of the thermocouples 4,6 and 10 compared to the thermocouples 2 and 7. Thermocouples 2 and 7 are located on the inlet side of the nitrogen channels resulting at the lower temperature at this location. Figure 6(d) shows the temperature profile measured in the center of the model during run 3 in the side walls of the central cooling channel. From this, a heat flux estimate can be calculated neglecting heat fluxes in X and Y direction on the surface as the temperature gradients in the center of the surface are significantly lower than the gradients in Z direction (see Fig. 6(b) and Fig. 6(d)). The resulting heat flux is approximately 3MW/m 2. The nearly linear temperature decrease in the cooling channel wall indicates a very small cooling effect of the gaseous nitrogen cooling channels Infrared Images The emissivity of the model was not known and the emissivity of cooper strongly depends on the state of the surface of the model. A surface temperature estimate was calculated from the temperature profile shown in Fig. 6(d) also neglecting heat fluxes in X and Y direction. The estimated surface temperature of 225 C leads to an emissivity of about Before run 2, the model was sandblasted to improve emissivity and avoid reflections. The measured temperatures for run 3 are shown in Fig. 8. It can be seen that the center of the model surface heated up during the wind tunnel run while the frame remained cold. After shut-down of the flow, the model cooled down quickly Deformation A test run with a prototype showed promising deformation results (Fig. 9(a)), but the geometry before the test had not been measured. After run 1 with the nominal model, no

7 Thermal Fluid-Structure Interaction of a Cooling Channel Configuration 269 (a) Model moved into flow field (b) 10s (c) 20s (d) 30s (e) 60s (f) 120s (g) 240s (h) 260s wind tunnel off FIGURE 8. Infrared measurement of the surface temperature - run 3

8 270 D. Daub, S. Willems, A. Gülhan & B. Esser Before run 1 After run 1 After sandblasting Z 1/ mm (a) Prototype test run Y 1/mm (b) Run 1 FIGURE 9. Deformation measurement significant difference to the state before the test was observed (Fig. 9(b)). The geometry also did not change significantly during the sandblasting. 5. Conclusions An experimental setup for the investigation of heat transfer and mechanical deformation of a generic cooling channel configuration was created and experiments were carried out in an arc-heated wind tunnel L3K. Various difficulties in manufacturing and test preparation were overcome. The cooling system was modified to withstand the high temperature flow field. The thermography setup was improved. The unsteady temperature distribution of the structure at the central cooling channel was measured. The hot gas wall deformation was measured before and after the experiments. The infrared images confirmed that the model design with cold frame and hot center cooling channel wall works as planned. Consequently, the experimental campaign will be concluded by investigating the thermomechanical effects occurring at temperatures above 400 C as well as at higher pressures in the nitrogen channels. For these conditions, structural deformations are expected. Acknowledgments Financial support has been provided by the German Research Foundation (Deutsche Forschungsgemeinschaft DFG) in the framework of the Sonderforschungsbereich Transregio 40. We gratefully acknowledge the help and advice of the technical staff of the Supersonic and Hypersonic Technology Department in Cologne. References [1] PASQUARIELLO, V., HICKEL, S., ADAMS, N., HAMMERL, G., WALL, W. A., DAUB, D., WILLEMS, S., GÜLHAN, A. (2015). Coupled simulation of shock-wave/turbulent boundary-layer interaction over a flexible panel. 6th European Conference for Aerospace Scienes (EUCASS), Krakow. [2] Hammerl, G., Seitz, A., Verdugo, F., Wall, W.A., Daub, D., Willems, S., Gülhan, A. (2016). FSI of rocket nozzles - On the influence of simplified modeling of structural

9 Thermal Fluid-Structure Interaction of a Cooling Channel Configuration 271 boundary conditions for an FSI experiment & scalable solvers for strongly coupled problems. SFB/TRR 40 - Annual Report [3] KOSCHEL, W. (2003). Flight Ariane 5 ECA: Report of the Inquiry Board. ESA Technical Report. [4] FASSIN, M., KOWOLLIK, D.S.C., REESE, S., LINDHORST AND HAUPT, M.C. (2015). Parameter identification and acceleration of fluid structure interaction based lifetime prediction for rocket engine nozzle structures. SFB/TRR 40 - Annual Report [5] TINI, V. (2014). Lifetime prediction of a typical rocket combustion chamber by means of viscoplastic damage modeling. Shaker Verlag. [6] CELANO, M.P., ROCHLITZ, H., HÖTTE, F., HAIDN, O.J., SCHOLZ, P. AND HAUPT, M.C. (2015). Experimental investigation on heat transfer of rocket combustion chambers and cooling channels. SFB/TRR 40 - Annual Report [7] GÜLHAN, A. AND ESSER, B. (2002) Arc-heated facilities as a tool to study aerothermodynamic problems of reentry vehicles. Advanced Hypersonic Test Facilities, Progress in Astronautics and Aeronautics, American Institute of Aeronautics and Astronautics, Reston. 198 (13), [8] WILLEMS, S., ESSER, B. AND GÜLHAN, A. (2015). Experimental and numerical investigation on thermal fluid-structure interaction on ceramic plates in high enthalpy flow. CEAS Space Journal. doi: /s