Tip clearance

About: Tip clearance is a research topic. Over the lifetime, 2637 publications have been published within this topic receiving 32671 citations.

Deterioration of compressor performance due to tip clearance of centrifugal impellers.

Abstract: The authors' theory on the tip-clearance loss of centrifugal impellers is modified to include variation of gas density in the impeller. Furthermore, a relationship between two empirical parameters in the theory is derived to reduce freedom of adjustment. In order to compare experimental data in the literature with prediction, examination was made regarding accuracy of data and the way to determine the corresponding flow rates at different tip clearances. Fair agreement between data and prediction was observed. These examples demonstrated effect of various parameters on tip clearance loss as follows. The clearance loss of high pressure-ratio compressors is less than that of low pressure-ratio compressors if the tip clearance ratio at the impeller exit is given. The clearance loss becomes smaller as the flow rate is reduced and also at a reduced shaft speed in cases of high pressure-ratio compressors. The equations in the theory clearly show these tendencies.

Unsteady Flow and Shock Motion in a Transonic Compressor Rotor

Abstract: The results of an experimental and numerical comparison of the unsteadiness and shock motion that occurs in the tip region within a modern, low-aspect-ratio, high-through-e ow, axial-e ow transonic fan rotor are presented. The unsteadiness studied here is associated with local phenomena within the blade passage and not related to blade row interaction. Unsteady static pressures were measured at the casing over the rotor that operates at a tip relative Mach number of 1.6. An unsteady three-dimensional Navier ‐ Stokes computational study was performed with tip clearance comparable to the test rotor. The fully three-dimensional, unsteady, Reynolds-averaged Navier ‐ Stokes equations were solved with time steps, each nominally of 2.8 3 10 25 s in duration or approximately e ve times blade pass frequency. The results in the clearance gap were retained from the computational solution and compared with the experimental measurements. Both indicated deterministic unsteadiness near the location of the shock. High levels of unsteadiness were also measured downstream of the shock in the path of the clearance vortex, but this phenomenon was not predicted by the computation. The unsteadiness near the shock was shown to be a result of movement of the shock. The amplitude and frequency of shock position oscillation was estimated from the results to be about 2% chord and 2 kHz, respectively. Analysis of loss caused by the shock unsteadiness suggested that losses because of shock motion were insignie cant relative to the steady shock loss at the relative Mach number studied.

Three-Dimensional Motion in Axial-Flow Impellers

Abstract: Detailed surveys have been made of the flow through a low-pressure-rise axial-flow impeller (hub/tip diameter ratio 0·33), which did not produce ‘free vortex’ whirl distribution.It was found that (1) at all flows, centrifugal forces caused large variations in axial velocity component through the rotor; (2) the angular direction of the flow varied considerably within a short distance of the rotor, and the flow did not stabilize until about two blade chords downstream; (3) as the tip clearance was increased, secondary motion was induced opposite to the motion caused by centrifugal effects and, for clearances greater than 1 per cent of the blade height, seriously restricted the use of radial equilibrium theory.The measured head-flow characteristics for various sections along the impeller blades did not agree well with those calculated by the following two-dimensional design methods: (1) ‘slip’ theory, (2) ‘cascade’ theory, (3) ‘aerofoil’ theory. Better results were given by the use of a new method which cons...

Numerical analysis of the tip leakage flow field in a transonic axial compressor with circumferential casing treatment

Abstract: This paper reports on numerical investigations aimed at understanding the influence of circumferential casing grooves on the tip leakage flow and its resulting vortical structures. The results and conclusions are based on steady state 3D numerical simulations of the well-known transonic axial compressor NASA Rotor 37 near stall operating conditions. The calculations carried out on the casing treatment configuration reveal an important modification of the vortex topology at the rotor tip clearance. Circumferential grooves limit the expansion of the tip leakage vortex in the direction perpendicular to the blade chord, but generate a set of secondary tip leakage vortices due to the interaction with the leakage mass flow. Finally, a deeper investigation of the tip leakage flow is proposed.