Title
Fabrication of Labyrinth seal test rig Ly Additive manufacturing
Field of invention
The present invention aims to find an alternative to the existing high weighing experimental test rig made up of heavy metals for identifying the leakage characteristics of labyrinth seals. A straight through le.byrinth seal is a popular non-contacting sealing tool for high pressure fluids which dissipates the energy of the flowing fluid by turbulent viscosity interaction achieved with a series of Seeth and cavities. The geometric parameters of straight through labyrinth seal directly impacts their leakage control performance. Numerous researches are going on to improve tfe performance of the seals by modifying the geometric parameters. The improvement in the waling performance has to be verified in an experimental test rig before it is incorporated iti the engineering applications. The present invention simplifies the fabrication of test rig through additive manufacturing instead of conventional methods.
Background of invention
The efficiency of the gas turbjie can be increased by decreasing the leakage flow rate. The contact seals which are best in p ^venting the leakage cannot be used in turbomachines as the moving parts will cause damage to the contact seals through friction. Therefore, non-contact sealing is a possible solution which increases the flow resistance for a specified pressure difference and reduces the leakage flew rate. Labyrinth seal, Pocket damper seal and brush seal are the various types of non-contaci seals available. Out of the non-contact seals available, Labyrinth seals is the most preferred "'."Lie to its simplicity in design and manufacture. Labyrinth seal is further classified into three categories - stepped, straight and staggered. Straight through

labyrinth seal is the basic type which is most frequently manufactured. When the fluid flows through the annular clearance region .above the tooth, the high-pressure head of the fluid to be restricted is converted to kinetic energy in the flow and the fluid comes out as a jet from the clearance. Only a portion of the jet enters the next clearance while the remaining part of the jet is dissipated by vortex generation in the cavities. As the fluid jet passes the tooth one by one, the kinetic energy of the jet is dissipated continuously resulting in leakage reduction.
The leakage control characteristics of the straight through labyrinth seal is improved by modifying the geometric parameters. Numerical analysis is used in the initial stage of research to improve the sealing which is to be validated by experiment testing. The test rig consists of a static outer chamber, rotating labyrimi i seal carrier and closing lids with provisions for pressure measurement and air inlet/outlet. The annular region between the seal carrier and the outer chamber forms the seal path which is to be investigated for better leakage control. The conventional manufacturing methods like facing, drilling and grooving is suitable for fabricating basic labyrinth flow path .«. ith perfect rectangular cavities. It is time consuming and expensive to fabricate complex labyihth shapes using conventional methods.
Additive manufacturing is :Ue process of computer-controlled creation of three-dimensional solids by depositing the materials usually in layers. Additive manufacturing also called as 3D printing supports the fabrication of complex labyrinth shapes at reduced time and cost. Polyethylene Terephthalate Gl-'iol (PETG) is the material chosen for fabrication using the Fused Deposition Modelling technique by maintaining the bed temperature as 80°C and the extruder temperature between 220°C and 260°C. Before the fabrication of seal carrier ' component with PETG, the capability of the material to withstand the force of the striking air up to a maximum pressure of 8 bar is tested in the ANSYS software. The maximum deformation of 3.9*10"7m is observeu for a maximum pressure of 8 bar thus making the test rig using PETG suitable for carrying i ait leakage analysis.

Brief description of drawings
Fig. 1 is the.3D model of the Labyrinth seal test setup
Fig. 2 is the cut section view of the Labyrinth seal test setup
Fig. 3 is the deformation plot for the labyrinth carrier using PETG material
Fig. 4 is the stator fabricated by additive manufacturing
Fig. 5 is the closing lids fabricated by additive manufacturing
Fig. 6 is the Labyrinth seal carrier fabricated by additive manufacturing
Detailed description of the invention
The 3D model of the labyrinth seal test setup is shown in Fig. 1. The outer casing encloses the seal carrier inside, the annular gap between both the components provides sealing for the flowing fluid. The seal carrier is locked inside the stator by closing lids on both sides. Fig. 2 is the cut section view of the labyrinth seal test setup which shows the annular flow path created between the labyrinth carrier and casing. With the help of additive manufacturing technique, any complex tooth and cavity geometry can be fabricated without much wastage of material and time.
Fig. 3 is the deformation plot from ANSYS for the seal carrier made up of PETG material which supports the use of 3D fabricated parts for Labyrinth seal testing. The dimension of the model taken for analysis is exactly same as the model used for experimental testing. Fig. 4, 5 and 6 shows the fabricated test rig components by additive manufacturing. The inlet lid consists of air entry points and provision for holding the seal carrier. The outlet lid consists of air exit points and a bearing at the centre to enable the labyrinth carrier to be connected to motor for rotary conditions. The components are assembled and subjected to air flow test up to a maximum pressure of 8 bar successfully. Thus, the present invention suggests a better method for the fabrication of test rig capable of testing highly complex labyrinth profiles.