The effect of incidence on the generation and growth of secondary flows in a linear turbine cascade was studied in the present investigations using a Variable Density Cascade Tunnel at an exit Mach number of 0.43 and a Reynolds number of 8 × 105. The angles of incidence chosen were +15°, +50, 0°, −5° and −8.5°. The flow field was surveyed at five axial stations from cascade inlet to exit with a view to understanding the development of the secondary flow with the help of the variation of mass averaged total pressure loss coefficient and the contours of local loss coefficients in the pitch and spanwise directions. The total pressure loss coefficient and the net secondary loss coefficient have shown a steady growth along the cascade upto about 74 of the axial chord from the leading edge and thereafter rose very rapidly. The incidence is found to have an effect on the passage vortex and the loss cores due to the inlet boundary layer.
A detailed study of flow through the blade passage and downstream of a linear turbine cascade was carried out for four cases of tip clearance including zero clearance. Apart from inlet traverse, a total of eight stations were chosen for inter-blade flow traversing between 5% and 95% of axial chord from leading edge. Downstream flow surveys were made at distances of 106% of axial chord from the blade leading edge. Pitchwise and spanwise traverses were conducted for each tip clearance at these stations using a small five hole probe. Provision was also made for the measurement of static pressure distribution on the suction and pressure surfaces and also on the blade tip surface when clearance is present. At about 40% of axial chord from the leading edge, the presence of clearance vortex is identified inside the passage. The growth of the clearance vortex in size, its movement towards the suction surface and its increase in strength with the gap size were observed beyond 55% of axial chord till the trailing edge region. The rate of growth of the losses in the endwall region increased with clearance. Horse shoe vortex was not observed for the highest clearance. The overall losses increase rapidly with clearance in the rear half of the blade.
This paper presents the results of experimental investigations on the three-dimensional flow and performance characteristics of a free vortex axial flow fan rotor, with a freely rotating and braked inlet guide vane row. The influences of axial distance between the inlet guide vane row and the rotor inlet, inlet guide vane setting angle and shape, partial omission of guide vanes at the hub and tip regions on the return flows have been studied and optimum axial distance and setting angle that will improve the useful operating range of the fan were determined. Use of freely rotating inlet guide vanes at high flow volumes and braked inlet guide vanes at low flow coefficients resulted in a reduction of return flows and an increase of the stable operating range of the axial fan rotor by more than 35 percent and this combination has yielded higher efficiencies as well in the extended region of stable operation.
Pressure measurements were carried out in an unshrouded radial inflow turbine in a closed circuit test facility, at nozzle inlet and exit, vis-a-vis rotor exit. Besides, blade surface pressures on the nozzle and rotor blades, wall static pressures on the back plate of nozzle and rotor blade passages, shroud static pressure variation along the casing from rotor inlet to exit were also measured for four different mass flows through the turbine. The increase of nozzle exit angle resulted in an increase of the stator loss coefficient at any mass flow rate. Rotor pressure measurements showed an adverse pressure gradient on the suction surface close to the hub region. Compared to the total pressure levels near the hub and shroud of the rotor passage, the pressure was higher at the mid height. The swirl at the rotor exit is somewhat stronger near the tip region as compared to the hub and the average loss is more towards the tip.
Two dimensional time averaged, steady incompressible, adiabatic turbulent asymmetric near and far non-periodic and periodic wake flow problems are solved by Galerkin Finite Element Method. A primitive-variables formulation is adopted using Reynolds-averaged momentum equations, with standard k-ε turbulence model. Finite element equations are solved by Newton-Raphson technique with relaxation, using frontal solver. Periodic boundary condition is specified on the periodic lines of the cascade, and asymptotic boundary condition is specified at the exit. These boundary conditions are applied without much difficulty which are not so straight forward in finite volume (FV) method. The results show good agreement with FV prediction and experimental data.
The paper presents the results of experimental investigations carried out on an unshrouded impeller of a centrifugal compressor to explore the possibility of improving the exit flow condition by the use of boundary layer fences and casing treatment. Eight different locations of fences were tried on the impeller vanes and hub surface. The boundary layer fences placed on the vane suction surface resulted in improvement of the exit flow condition. A combination of grooves and the fences on the front casing cover near the inlet and tip of the impeller was also investigated.
The paper presents the results of three dimensional flow measurements behind the trailing edges of an impulse turbine blade row of 120° deflection in an annular cascade. The entry boundary layer thickness was systematically varied on the hub and casing walls separately and its effect on secondary flows and losses is investigated. With the increase of entry boundary layer thickness, it has been found that (i) the contours of local loss coefficient show that the magnitude of the hub loss core increased, (ii) the loss cores near the hub and casing wall are convected away from the walls, (iii) the spanwise variation of the pitchwise averaged losses indicate that the position of large loss peak near the hub wall remains the same, but the magnitude of the loss increases, (iv) the exit static pressure increases and the exit velocity in general decreases, (v) the degree of underturning of flow increases and (vi) the net secondary losses do not change appreciably.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.