Experimental and Computational Investigation of Flow Structure in Buoyancy Dominated Rotating Cavities

Abstract

The flow and heat transfer inside HP compressor rotating cavities are buoyancy driven and are known to be extremely difficult to predict. The experimental data of Laser-Doppler Anemometry (LDA) measurements inside an engine representative cavity rig is presented in this paper. Traverses using a two component LDA system have been carried out in the shaft bore and the cavity regions in order to map the axial and tangential velocity components. The velocity data is collected for a range of Rossby, Rotational and Axial Reynolds numbers, Ro, Reθ and Rez: 0.08 < Ro < 0.64, 7 × 105 < Reθ < 2.83 × 106, 1.2 × 104 < Rez < 4.8 × 104 and for values of the buoyancy parameter βΔT, 0.284 < βΔT < 0.55. Numerical study using unsteady Reynolds Averaged Navier-Stokes (URANS) simulations have been carried out to elucidate flow details for a few selected cases. The experimental results revealed that the Swirl number (Xk) varies from a value < 1 near the bore to near solid body rotation at increased radii within the cavity. The analysis of frequency spectrum of the tangential velocity inside the cavities has also shown the existence of pairs of rotating and contra-rotating vortices. There is generally satisfactory agreement between measurements and CFD simulations. There is also convincing evidence of two or more separate regions in the flow dominated by the bore flow and rotation.

Unsteady Pressure Measurements in a Heated Rotating Cavity

“…0) covers a smaller angle, but with a greater pressure magnitude than that of the cyclonic vortex (Cp < 0). This finding is consistent with those of other experimental and computational researchers [5,10,13]. The second frequency mode in Fig.…”

“…They calculated the slip of the core to be around 6% using the measurements from unsteady pressure sensors on the stationary shaft. Simulations produced by Fazeli et al [5] demonstrate the instability of the flow field, showing a vortex structure which changes between one and two pairs over time; they validated the number of structures using spectral analysis techniques on LDA velocity measurements.…”

“…It may be possible that a second, smaller vortex pair does exist, but at a radius lower than that of the sensor location. Smaller, secondary cyclonic vortices are shown in the results of some numerical simulations [5,13]. Figure 7 also shows that the vortices can deviate from the dominant rotational frequency, highlighting their unsteadiness.…”

“…The frequency spectra from the Fourier transform of the pressure measurements are shown in Fig. 6 for an example case where Reϕ = 8x10 5 , βΔT = 0.28, Gr = 1.9x10 11 and Ro = 0.2. The frequency is normalized with respect to the rotational frequency of the discs (fd).…”

“…GTP-21-1401 Jackson 4 vortex forms in the inner (low radius) region, as the throughflow impinges on the downstream disc and recirculates. The existence of the toroidal vortex in a heated cavity has been demonstrated using velocity measurements [4,5], heat transfer measurements [6 -8] and computations [9].…”