Numerical Investigation of Vaneless Diffuser by Pinching and Rotation

Abstract

Non-conventional diffuser designs are introduced to minimize the energy losses associated with diffusion and to enhance stable operating range of the diffusion system. This is achieved by reducing width of the diffuser by modifying a hub or shroud curves by keeping the diffuser diameter ratio constant which is often known as pinch. The comparison of modified compressor with base model is accomplished by using performance characteristics such as static pressure recovery coefficient, stagnation pressure loss coefficient, energy coefficient and isentropic efficiency. Simulations are performed at various hub pinch (5%–20%), shroud pinch (5%–20%) and combined hub and shroud pinch (5%–20%). Among all the cases shroud pinch of 10% shows best results in terms of stagnation pressure loss coefficient, static pressure recovery coefficient and energy coefficient. Further, simulations are carried out with forced rotating vaneless diffuser. It gives better results in terms of pressure rise with lower stagnation pressure losses. But there is a moderate decrement in isentropic efficiency of compressor when compared to the base model.

Numerical investigation on the combined effects of pinching and rotation on the performance of a high-speed centrifugal compressor with a vaneless diffuser

“…The k-ɷ based SST turbulent model is used with high-resolution turbulence numeric and advection scheme. The authors concluded in ref 18 and koumoutsos et al 19 that this method gives the best results for the current class of problems. Steady state simulations are carried out by setting the time scale factor to one second.…”

“…In the rotating pinched diffuser with a diameter ratio of 1.375, diffuser effectiveness is higher for the entire operating than base model (SVD) and stationary pinch diffusers. 18 The rate of increase of the static pressure in rotating pinched diffusers is higher due to the transformation of energy in the diffuser flow domain. Shroud pinch (5%-20%) with diffuser diameter ratio 1.375, 5% pinch has given lower performance, and 10% and 15% pinch has shown better performance.…”

“…However, most of the recent centrifugal compressors used in aircraft engines are of exceptionally high speed, more than 40, 000 rpm, and the Mach number at the entry of the diffuser is more than 0.45–0.7. The authors in 18 present the lone work with very high-speed centrifugal compressor with a stationary diffuser with shroud pinching.…”

Computational Analysis on the Performance of Centrifugal Compressor with Tapered Wall and Rotating Tapered Wall Vaneless Diffuser

“…Better output out of all cases was demonstrated in TaperedSVD1 and TaperedSVD3. Due to the secondary flows in the diffuser which are caused by higher pressure gradients and additional energy transfer, the isentropic efficiency of the compressor is lower in the case of rotating diffuser Niveditha et al (2019). Figure 22 displays isentropic efficiency curves which are comparable to the tapered rotating diffuser.…”

“…Following parameters, expressed in Eqs. (8) -(12), taken from previous research (Niveditha et al 2019) and (Seralathan et al 2017), are used to compare the performance of various configurations of the compressor with the base model.…”