A numerical investigation of moment coefficient and flow structure in a rotor–stator cavity with rotor-mounted bolts

Abstract

The torque associated with overcoming the losses on a rotating disc is of particular importance to the designers of gas turbine engines. Not only does this represent a reduction in useful work, but it also gives rise to unwanted heating of metal surfaces and the adjacent fluid. This article presents a numerical study on the effect of rotor-mounted bolts on the moment coefficient and velocity distributions within a rotor–stator cavity under conditions representative of modern gas turbine engine design. Steady-state, two-dimensional and three-dimensional, computational fluid dynamics simulations are obtained using the FLUENT commercial code with a standard k–ɛ turbulence model. The model is validated against experimental data and then used to investigate the effects of varying the number of bolts and also a continuous ring. Two test cases are investigated: one corresponds to where the flow structure is dominated by the superimposed flow (λT = 0.35); and the other, where rotation is expected to govern the flow structure (λT = 0.35). The principal flow phenomena in the vicinity of the bolts were described using the simulation results. Increasing the number of bolts will decrease the relative total pressure difference around bolts and increase the tangential velocity of the core of fluid between the rotor and stator. It was also found out that the free-stream Reynolds number of the flow approaching the bolts decreases and angle of attack increases with increasing number of bolts. As a consequence, the bolts’ wake character changes leading to a situation where the wake of one bolt is not fully collapsed in advance of the following bolt. The occurrence of Taylor columns were also investigated in the rotor–stator system with rotor-mounted bolts. It was found that while increasing the number of bolts can decrease the Rossby number to produce an intermediate rotation in the system, the Taylor columns will not be produced even for 60 bolts under the both flow conditions. The contribution of skin friction to the overall moment coefficient reduces as the number of bolts increases and the pressure-related losses increase. Increasing the number of bolts will decrease the moment produced by each individual bolt. However, since there are more bolts in the system the total moment of all bolts will increase by increasing their number. There also appears to be a point where increasing the number of bolts does not bring about an increase in the overall moment coefficient. It is also interesting to report that the moment coefficient associated with a continuous ring is similar to that for a plain disc.

Windage Measurements in a Rotor-Stator System With Superimposed Cooling and Rotor-Mounted Protrusions

“…Figure 17 shows a comparison between the measured values of moment coefficient of all six configurations and those predicted by Eq. (20). There is a good agreement, generally within 6%, between the measured and the correlated data.…”

“…Coren et al, (2007) [18] and Miles (2012) [19] carried out an experimental study on windage effects in rotor-stator cavities for both plain disk and the rotor with protruding bolts. Moghaddam et al (2013) [20] conducted a numerical study that showed that the moment coefficient increased significantly with an increasing, yet limited, number of bolts. Long et al (2012) [21] carried out experiments with hexagonal and bihexagonal rotor bolts and a single design of rotor pocket.…”

“…0.02 (20) This new correlation primarily focuses on the turbulent flow parameter for analyzing the moment coefficient in a rotor-stator system. Meanwhile, the influence of geometry is taken into account for the correlation to extend the range.…”

Flow and windage due to bolts on a rotating disc

“…Moghaddam et al. 20 investigated the effect of bolts on the rotor surface, on moment coefficient, and the flow structure, in a shrouded rotor–stator system with superimposed throughflow. The steady CFD simulations were carried out using periodic sector models varying the number of bolts in the range 0 ≤ n ≤ 60.…”

“…The CFD studies on disc cavities with bolts or protrusions have focused primarily on the validation of predicted disc torque by comparison with measured values, assuming that the flow is steady and periodic. Moghaddam et al 20 investigated the effect of bolts on the rotor surface, on moment coefficient, and the flow structure, in a shrouded rotor-stator system with superimposed throughflow. The steady CFD simulations were carried out using periodic sector models varying the number of bolts in the range 0 4 n 4 60.…”