Numerical investigation on body-wake flow interaction over rod–airfoil configuration

Abstract

Numerical investigations of body-wake interactions were carried out by simulating the flow over a rod-airfoil configuration using high-order implicit large eddy simulation (HILES) for the incoming velocity U ∞ = 72 m s −1 and a Reynolds number based on the airfoil chord 4.8 × 10 5 . The flow over five different rod-airfoil configurations with different distances of L/d = 2, 4, 6, 8 and 10, respectively, were calculated for the analysis of body-wake interaction phenomena. Various fundamental mechanisms dictating the intricate flow phenomena including force varying regulation, flow structures and flow patterns in the interaction region, turbulent fluctuations and their suppression, noise radiation and fluid resonant oscillation, have been studied systematically. Due to the airfoil downstream, a relatively higher base pressure is exerted on the surface of the cylinder upstream, and the pressure fluctuation on the surface of the rod-airfoil configuration with L/d = 2 is significantly suppressed, resulting in a reduction of the fluctuating lift. Following the distance between the cylinder and airfoil strongly decreases, Kármán-street shedding is suppressed due to the blocking effect. The flow in this interaction region has two opposite tendencies: the influence of the airfoil on the steady flow is to accelerate it and the counter-rotating vortices connecting with the leading edge of the airfoil tend to slow the flow down. There may be two flow patterns associated with the interference region, i.e. the Kármán-street suppressing mode and the Kármán-street shedding mode. The primary vortex shedding behind the cylinder upstream, and the shedding wake impingement onto the airfoil downstream, play a dominant role in the production of turbulent fluctuations. When primary vortex shedding is suppressed, the intensity of impingement is weakened, resulting in a significant suppression of the turbulent fluctuations. Due to these factors, a special broadband noise without a manifestly distinguishable peak is radiated by the rod-airfoil configuration with L/d = 2. The fluid resonant oscillation within the flow interaction between the turbulent wake and the bodies was further investigated by adopting a feedback model, which confirmed that the effect of fluid resonant oscillation becomes stronger when L/d = 6 and 10.The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the body-wake interaction.

A rod-linear cascade model for emulating rotor-stator interaction noise in turbofans: A numerical study

“…6, in which the spanwise coordinate has been non-dimensionalized with rod diameter D. The fine case is shown to produce good agreement against other experimental measurements on isolated rod at subcritical Reynolds number range [42,47]. The discrepancies that are present might be attributed to the weak feedback from the airfoil downstream as observed by Jiang et al [15].…”

“…The forces are expressed as lift and drag coefficients with respect to the local coordinate system. The rod C D,mean is within the expectation of an isolated rod [41,47] and the rod in the RAC [15]. The mean lift and drag on all blades are almost identical, except for the central blade that is under the rod wake influence.…”

“…18 (i) since the rod-central blade separation is 8D in present case. The rod of the RLC also show very similar pressure distribution compared to that of the RAC [15,54], which may imply that the cascade of the RLC does not affect the rod differently than that of the RAC.…”

“…18. Jiang et al [15] has previously observed that as the separation between the rod and the downstream body becomes larger than 6D, the rod pressure distribution approaches that of an isolated rod. This is consistent with the present result in Fig.…”

“…The rod-airfoil configuration (RAC) has been quoted to be suitable for emulating the rotor-stator interaction mechanism due to the quasi-tonal and broadband excitation induced by the rod wake onto the airfoil [7,8,[10][11][12]. The classical RAC consists of a rod positioned upstream of an airfoil, and it was introduced as a benchmark configuration for computational aeroacoustics (CAA) studies on turbulent wake-body interaction [7,[13][14][15][16]. However, there are various features inherent of the rotor-stator aeroacoustics which are absent in the RAC due to the usage of the isolated, symmetrical airfoil; two among which will be addressed in this manuscript.…”