PSI - Issue 17

Shahnawaz Ahmad et al. / Procedia Structural Integrity 17 (2019) 758–765 Shahnawaz Ahmad/ Structural Integrity Procedia 00 (2019) 000 – 000

760

3

in Figure 4. Time has been normalized as 100 s s tn   = where s  is the rotational frequency of the rotor in rev/sec. Forcing frequency, for this simulation is taken as 100 Hz. The maximum pressure on the blade’s pressure surface was observed to be approximately 1.8 MPa, and the minimum was 1.2 MPa

Table 1Flow Conditions Parameters Value Design mass flow rate 105 kg/s Ambient temperature 288.15 K T inlet 1348 K T outlet 1144 K P inlet 12.06 bar P outlet 5.49 bar Number of nozzles 53

Figure 3Pressure distribution of air around the blade profile

Figure 2Flow across a blade passing through 2 nozzles

The periodic nozzle forces F ( t ) on the blade can be expressed in terms of pressure in Fourier form as:     0 6 { }cos { }sin aerodynamic m m m m F F F mvt F mvt + = + +   …

(1)

The Fourier components are listed in Table 2.

Table 2Fourier components of forcing function

m

F m (bars) 15.410

F m+6 (bars)

0 1 2 3 4 5 6

0

1.306 0.144 -0.192 0.071 0.340 0.059

2.996 -0.833 0.288 0.491 0.270 -0.025

Figure 4Maximum pressure variation on the blade surface

2.2. Transient and steady state stress analysis A gas turbine engine undergoes both -constant rotor speed operation and variable rotor speed operation as in the case of starting up or shutting down or while performing other maneuvers. The equation of motion for the forced vibration can be rewritten as: (2) The gas turbine engine generally operate at two speeds; (i) the idle speed, and (ii) the cruising speed, which for the engine in analysis are10400 rpm and 12300 rpm respectively. A typical transport aircraft AMT (Accelerated Mission Test) cycle has been utilized for getting operating parameters. The operating cycle with initial takeoff conditions in focus, are shown in Figure 5 and Figure 6, respectively. Stress computation, under flow path excitation forces is carried out for resonance conditions. Damping was calculated as 2% i.e. 0.02, by the half power bandwidth rule from the frequency response curve obtained by the experiments. These centrifugal force caused due to rotation of the bladed disc, is determined as 2 ( ) centrifugal F m R z  = + (3) where  is rotational speed of the shaft (in rad/s), m is the mass of the element, R radius of the rotor disc and z distance from the root to the center of gravity of element. The variation of centrifugal stresses with the rotational speed is quadratic. This force adds to the mean stress load carried by blade, which are computed at rotating speeds of 10400 rpm (idle speed) and 12300 rpm (max. cruising speed). All material data was taken from tests conducted on