Design and Manufacturing Trials for a Combustor Case with Active Cooling Air Cooling

Transcription

1 Design and Manufacturing Trials for a Combustor Case with Active Cooling Air Cooling Presenter: Gunnar Marke, Volvo Aero Contributor: Göran Johnsson, Volvo Aero Wolfgang Sturm, MTU

2 Introduction Purpose The purpose with the work have been to design and manufacture/modify a combustor case for an Active Cooling Air Cooling (ACAC) system. What is an ACAC-system? An ACAC-system is a system where the cooling air to the turbine is cooled by the by-pass air. The system is active, i.e. the degree of cooling can be adjusted by a valve and a control unit. Bypass Air Heat exchanger Valve Cooled Cooling Air

3 Introduction Design iterations First iteration: Design of a combustor case for a virtual NEWAC -engine in the thrust range of 30klbs. Second iteration: Adoption of the concepts from design iteration one, onto a Volvo engine planned for engine testing. The full ACAC-system was studied in order to perform an engine test financed outside NEWAC. Third iteration: More generic manufacturing approach to find a way of manufacture a competitive combustor case for ACAC.

4 Introduction Partners involved Following partners have been involved in the work: System lead Combustor case design Weight offset Virtual Multi Beam Ultrasonic Shot Heat exchanger Distribution of flow Ti-Al EB Welding Peening Turbine analyses Re-heating of flow Concept Pressure losses Concept System for VAC eng. Manufacturing aspects

5 Concept iteration 1. Several concepts where developed in the first iteration, see deliverable D4.2.3A Selected concept is shown to the right: Early omitted concept.

6 Design iteration 1 To design a combustor case for an ACAC-system, the pressure losses must be minimized. In order to minimize the pressure losses a study was performed on different ways of feeding the cooled air from the heatexchanger to the turbine. The different geometrical restrictions in the system was defined, to obtain the right flow balance. C A B D

7 Design iteration 1 (Diffusor design) In most cases, one of the limiting factors are the cross-sectional area through the diffusor. For the initial work, the design parameters where quite free and the diffusor was designed to accommodate large enough cooling tubes through the diffusor struts. Requirements for the diffusor design where: - Max pressure drop over the diffusor = 2,2 % - Maximum Mach number at diffusor outlet = less than 0,13. - Maximum length of diffusor = 80 mm A diffusor design that could accommodate a tube diameter of mm was developed.

8 Design iteration 1, cont. In order to make the ACAC-system to deliver the required coolingflow without adding an airpump a requirement regarding pressure losses for the cooling air, between heat-exchanger (HX) and entry to turbine of 6% was set. Another requirement was that the cooling should not be allowed to be reheated more that 30 K. Due to the type of flow in the cavities, a test was set up to verify the heat transfer analysis model. Inlet 1 Several design iterations where made with different concepts, The analysis model of selected concept is described to the right: 5 mm radius Outlet 1 Φ 18 mm VAC TBC Outlet 3 Rotating walls Outlet 2

9 Concept iteration 2. During iteration two (VAC engine) the concepts where modified to fit to the VAC engine, see below: Due to the restriction of not affecting the axial balance of the rotor shaft a tube solution was selected.

10 Design iteration 2 (VAC engine for engine test). Now the design was restricted to fit the actual engine. No modification could be made to the diffusor and the risk of affecting the total balance of the rotor should be minimized. 1-D Heat exchanger analysis's shows that the assumed cooling of 200 K can be fulfilled with 3 tubular heat exchanger. Geometrical packing of the heat exchangers in the bypass channel might be a problem, at least for a military engine. Bypass flow Core flow

11 European Workshop on New Aero Engine Concepts Design iteration 2 (VAC engine for engine test). The weight/geometry of the heat exchangers will be a key issue. Modifications to the combustor case was necessary to accommodate the tubing. Holes was introduced and/or increased, bosses where added. The bosses to be added by LMD (Laser Metal Deposition). Stress analyses of introduced bosses showed a significant increase in local stresses, but no showstopper for a test. Original RM12 Combustor case Number of elements: Shell elements: 8223 Tetra elements, original: Tetra elements, with boss: Model with boss

12 Testing Heat transfer testing - VAC have performed heat transfer testing at Lund University to verify the analytical heat transfer results. CFD Product Rig channel Suction fan Metal Deposition - INCO718 material for combustor case. - Initial Metal Deposition was performed with TIG (SMD). - Due to that Metal Deposition on Titanium showed better results with Laser Metal Deposition, the process was changed to LMD. - Initial tests on sheet metal showed promising results. - LMD on actual combustor case was performed. Air intake

13 Results Heat transfer testing Good agreement between heat transfer analyses and testing was obtained. Data and CFD agree reasonable well HTC predictions judged to be within 25 % CFD Product Validation results Nu/Nu_max test Norm alize d Nu ve rs. norm alized x 1,2 1,1 1 0,9 0,8 0,7 0,6 0,5 0,4 0,8 0,9 1 1,1 1,2 1,3 1,4 x / x peak location Resolved realizable k-epsilon Wall function realizable k-epsilon Resolved k-omega SST (UD) TEST DATA

14 Results LMD VAC have experience of adding bosses by Laser Metal Deposition (LMD) on Titanium structures. Applying that experience to a different material, INCO718, showed up to not be as easy as hoped. Initial trials on plates showed promising results. When applying bosses on an actual combustor case (INCO718 material) different types of cracks occurred. One reason for this is that sheet metal is free to deform, while the actual part is restricted to absorbed deformations. Bosses added by LMD on used combustor case Note: This is not a crack!

15 Comparison of achieved results and target objectives. Requirements regarding pressure losses in tubes (Through the combustor case) after the heat-exchanger (6%) can be fulfilled for both design iteration 1 and 2. Requirements regarding Re-heating of cooling flow.(through the combustor case) shall not exceed (30/50 K) can be fulfilled for both design iteration 1 (30K) and 2 (50K). Thermal barriers coating are required for some cases. Heat-exchanger analysis's shows that the assumed cooling of 200 K can be fulfilled with reasonable sized tubular heat-exchangers. Harder than expected to obtain crack free bosses on INCO718 by LMD.

16 Conclusion & outlook The ACAC-system shows promising results. (SFC improvement 1,5 %) The key to achieve a good combustor case design is to be able to manage the large amount of bosses on the casing. Large complicated castings will lead to low flexibility during the designphase and a monopoly situation with very few possible casters. A fabricated structure must incorporate a large number of bosses for the ACAC-system, not to mention fuel nozzles, igniters, boroscope ports, etc... The parameters for the initial LMD tests and CRF bosses have been revised from a crack reduction point of view and a number of new basic test trials have resulted in a new set of parameters for the next LMD boss trials.