So for the blades you are constrained to have casted materials that have directionally oriented grains parallel to airfoil axis (aka DS or SC) - but that's not all, due to high-temp operating env, it needs to have a good ability to accept TBC as well (plus higher oxidation resistance properties - again more on this on a later day). So for the disk you would ideally be looking for some material with very good tensile ductility, high tensile yield and ultimate strength (and LCF too - more on this on some other day) - while the temp operating environment gives you a lot of leeway (compared to blades), so much so you can get away with even equiaxed-casted materials.īut for the blades the requirements are high Thermal Mechanical Fatigue (TMF) resistance (aka higher melting points), Creep-rupture strength and HCF - while lot of leeway on mechanical strength aspects like tensile yield/strength and ductility. So the mechanical pressure due to good-old centrifugal force on a disk is multiple times more than that of the blades - but the operating temp regime is also very different. Mass - easily 10-12 times of Blades (cumulative)Ĭycle Fatigue - Low - High(will explain this in a later post) So between the disk and the blades of the same HPT stage, you have the following:įactors - Disk - Blade Now if you compare the mass of the disk and that of the blades, it's obvious that the mass of disk is many order-of-magnitude more than that of the blades. Look at the picture of an military turbojet/fan HPT, for example that of a F-110 as shown below: But what about the disk - the temp there seldom will reach beyond 800-900 deg C and speed maybe 0.9M.īig difference, isn't it? But that's not all.
Let's look at a HPT stage of a Turbine - now the blades will be required to withstand 1600-1700deg C temp and tip-rotor speed of about 1.5M. I'll not go into too much detail (will reserve that for Material write-up, if it ever gets finished - most likely it won't, just like my engine-design related write-ups - all lying around at 50-60% completion level ), let me try to bring out a small dichotomy (in context of blisk manufacturing usage). What never gets discussed or thought thru is what it really means in terms of constraints that are being tried to overcome. How many times here in BR we have heard that if only we could have mastered Blisk-manufacturing technology, most (if not all) issues of Kaveri would be sorted. There's simply no other choice - 2nd (1a-2b) and 3rd (1b-2a) quadrant choices couldn't have been taken, as in the late 80s (when this decision was being taken) the status of,ġ) Prevalent Materials R&D and, more importantly, indigenously available manufacturing and engineering base to translate these designs to manufactured parts/products etc.Ģ) Low experience on the mechanical and CFD (from non-flying testbeds like GTX-37U and UB etc.) aspects of an aero-engine design Given that the Kaveri is to be used in IUSAV (the unmanned strike platform), do you think that the conservative design choice was the right one? After all, because GTRE went with the conservative choice, at least India will soon have an engine it can use for other purposes, apart from the Tejas.Īvarachanji, reg the conservative engine technology roadmap for Kaveri, selected by the GTRE folks, well, let me put it this way. Avarachan wrote:Maitya, thank you for these very informative posts.
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