Recommendations for Achieving Accurate Numerical Simulation of Tip Clearance Flows in Transonic Compressor Rotors

Abstract

The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. While numerical simulations of these flows are quite sophisticated, they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip-clearance flow details (e.g. trajectory and radial extent) with corresponding data obtained from a numerical simulation. Recommendations for achieving accurate numerical simulation of tip clearance flows are presented based on this comparison. Laser Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor was simulated using a Navier-Stokes turbomachinery solver that incorporates an advanced k-ε turbulence model derived for flows that are not in local equilibrium. Comparison between measured and simulated results indicates that simulation accuracy is primarily dependent upon the ability of the numerical code to resolve important details of a wall-bounded shear layer formed by the relative motion between the over-tip leakage flow and the shroud wall. A simple method is presented for determining the strength of this shear layer.

Low-Cost Rotating Experimentation in Compressor Aerodynamics Using Rapid Prototyping

“…hub clearance of 1.62% hub chord), and mixed flow rotor (max. tip clearance of 1.28% tip chord) were, respectively, 24, 38, and 96, all of which surpass the criterion proposed by Van Zante et al [4] for adequate capture of tip clearance flow. + value at the solid surfaces goes from below 1 up to 6.…”

“…On the other hand, one may choose to use an existing in-house compressor rig to perform new specific tests for code assessment. Van Zante et al [4] performed tip clearance flow LDV measurements on an existing NASA Rotor 35 to assess the accuracy of numerical tip clearance flow predictions. To validate numerical simulations of more complex compressors, Mansour et al [5] and Cornelius et al [6] validated their computational solutions with measurements obtained from their multistage transonic compressor rig.…”

The choice of key geometric parameters in the numerical optimization of centrifugal compressor impellers

“…It should be noted that, in addition to the analysis of geometric parameters, the selection of parameters of the calculation model, such as: the computational domain, grid parameters, boundary conditions, solver settings, etc., is of great importance in solving the optimization problem [15][16][17][18][19][20].…”

Impact of the tip vortex on the passage flow structures of a jet fan with symmetric blades

“…Recently, computational fluid dynamic (CFD) techniques have been also introduced as a powerful tool to characterize the impact of tip leakage structures onto the passage-averaged flow. Some strategies assume that there is flow periodicity across a non-gridded region above the blade tip, whereas others consists in fully gridding the gap with a separate grid block [15,16]. In case of gridding the gap, the model requires intensive computational resources due to the near-wall grid spacing recommended for the tip gap.…”

“…In case of gridding the gap, the model requires intensive computational resources due to the near-wall grid spacing recommended for the tip gap. It has been demonstrated that such a grid distribution has a significant impact on accurate prediction of the clearance flow [16].…”