Effect of swirl flow on the performance of parallel hub axial annular diffuser

In the present work, the parallel hub axial flow annular diffuser's performance characteristics with divergent casing varying between equivalent cone angle (10°, 15°, and 20°) with area ratio 3 have been evaluated computationally as well as experimentally. The performance of three diffusers were tested at different inlet swirl angles (from 0° to 25°) for swirling and non-swirling flow. Simulations have been carried out on a fully developed flow at Reynolds number 2.5×105. The results were analyzed based on the velocity profiles, static pressure recovery coefficient, and the total pressure loss coefficient. The result analysis shows that the inlet swirl flow improves the recovery of pressure and also delays the flow separation on the casing. Moreover,the findings also show that the best performance was achieved in equivalent cone angle 10° at the inlet swirl angle of 7.5° compared to other diffusers.

Making Better Swirl Brakes Using Computational Fluid Dynamics: Performance Enhancement From Geometry Variation

A fluid with a large swirl (circumferential) velocity entering an annular pressure seal influences the seal cross-coupled dynamic stiffness coefficients and hence it affects system stability. Typically comprising a large number of angled vanes around the seal circumference, a swirl brake (SB) is a mechanical element installed to reduce (even reverse) the swirl velocity entering an annular seal. By using a computational fluid dynamics (CFD) model, the paper details a process to engineer a SB upstream of a sixteen-tooth labyrinth seal (LS) with tip clearance Cr = 0.203 mm. Rather than relying on extensive experiments, the CFD analysis proves effective to quickly engineer a best SB configuration from the quantification of performance while varying the SB geometry and inlet swirl condition.

A Novel Hybrid Seal: Design and Experimental Validation on a High Pressure Rotordynamic Test Rig

The design and experimental activity presented in this paper is related to a novel hybrid seal which is intended to work as a balance piston seal in an AMBs levitated high-pressure (about 300 bar delivery pressure) motor-compressor. The typical solution adopted for balance piston application is a damper seal (e.g. honeycomb seal), as the rotordynamic stability is a primary focus. However, due to interactions between the AMB controller and seal high stiffness level, the aforementioned selection is not so straightforward. After a review of the state of the art it was found that a combination of some conventional geometries (e.g. labyrinth and honeycomb) can be adopted to achieve the desired target. The design was done using a novel tool combining the validated bulk flow codes for each geometry. Moreover, a CFD analysis, based on some literature references, was carried out as a final verification of the design. The experimental activity was then performed at the Authors’ internal seal test rig. As in typical rotordynamic seal testing activity, the operating parameters leveraged to explore performance sensitivity are rotational speed, inlet pressure, pressure ratio and inlet swirl level. The outcome was satisfactory both in terms of leakage and rotordynamic coefficients.

Numerical Investigations on the Aerothermal Performance and Film Cooling Effectiveness of Turbine Vane Endwall at Inlet Swirl Conditions

Lean burn premix technology of gas turbines results in that the turbine combustor outlet has strong swirl flow characteristics which directly influences the inlet flow condition of the first turbine vane downstream from combustor and raise the thermal load of endwall. The aerothermal performance and film cooling effectiveness of first turbine vane endwall at different inlet swirl conditions is numerically investigated in this paper. The flow pattern, Nusselt number distribution and film cooling effectiveness of turbine vane endwall at the uniform and three kinds of swirl numbers (0.6, 0.8, 1.0) inflow conditions with clockwise and anticlockwise swirl orientations are analyzed using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and SST k-ω turbulence model solutions. The obtained results show that the flow field is apparently influenced by inlet swirl conditions. The separation in passage is clearly suppressed at clockwise swirl inflow conditions but anticlockwise make the flow pattern more complex. Inlet swirl can increase the overall Nu on the endwall. Especially in the area upstream of leading edge and area between the first and second row of film holes whose Nu are increased by 4 and 1.5 times compared with uniform inflow, respectively. Not only swirl number but also orientation can affect the film cooling effectiveness distribution of the vane endwall. The better film cooling effectiveness distribution and higher film cooling effectiveness downstream of each film hole row can be achieved at the clockwise swirl inflow conditions by weakening the accumulation of coolant near the suction side of the turbine vane endwall. Compared with uniform inflow, average film cooling effectiveness of endwall between the second row and third row is increased from 0.21 to 0.27 at clockwise SN = 1.0 for the maximum increase. The detailed flow field and aerothermal performance of the turbine vane endwall at different swirl inflow conditions is also discussed and illustrated.

Performance characteristics of flow in annular diffuser using CFD

An annular diffuser is a critical component of the turbomachinery, and its prime function is to reduce the flow velocity. The current work is carried to study the effect of four different geometrical designs of an annular diffuser using the ANSYS Fluent. The numerical simulations were carried out to examine the effect of fully developed turbulent swirling and non-swirling flow. The flow behavior of the annular diffuser is analyzed at Reynolds number 2.5 × 105. The simulated results reveal pressure recovery improvement at the casing wall with adequate swirl intensity at the diffuser inlet. Swirl intensity suppresses the flow separation on the casing and moves the flow from the hub wall to the casing wall of the annulus region. The results also show that the Equal Hub and Diverging Casing (EHDC) annular diffuser in comparison to other diffusers has a higher static pressure recovery (C p = 0.76) and a lower total pressure loss coefficient of (C L = 0.12) at a 17° swirl angle.