Effects of swirling inlet flow on pressure recovery in conical diffusers

McDonald, Alan; Fox, Robert W.; Dewoestine, Robert V. Van

doi:10.2514/3.6456

Cited by 64 publications

(16 citation statements)

References 3 publications

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“…Figure 15 compares exhaust hood inlet swirl angle distributions published in some of the existing literature. The effect of swirl angle on the pressure recovery of annular diffusers has been widely explored in the works of Kumar and McDonald [43,44]. Swirl was proven to have a positive effect on the performance of a separated diffuser by suppressing the separation, compared with the axial case, however, this positive effect deteriorates at high swirl angles.…”

Section: Swirl Angle Distribution Downstream Of Thementioning

confidence: 98%

A Literature Review of Low Pressure Steam Turbine Exhaust Hood and Diffuser Studies

Burton¹,

Ingram²,

Hogg

2013

Journal of Engineering for Gas Turbines and Power

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This paper summarizes the findings from research studies carried out over the last 30 years, to better understand the flows in steam turbine low pressure exhaust hoods and diffusers. The work aims to highlight the areas where further study is still required. A detailed description of the flow structure is outlined and the influence of the last turbine stage and the hood geometry on loss coefficient is explored. At present, the key challenge faced is numerically modeling the three-dimensional, unsteady, transonic, wet steam exhaust hood flow given the impractically high computational power requirement. Multiple calculation simplifications to reduce the computational demand have been successfully verified with experimental data, but at present there is no 'best-practice' approach to reduce the computational time for routine design exercises. This paper highlights the importance of coupling the exhaust hood to the last stage steam turbine blades to capture the interaction; ensuring the total pressure and swirl angle profiles, along with the tip leakage jet are accurately applied to the diffuser inlet. The nonaxial symmetry of the exhaust hood means it is also important to model the full blade annulus. More studies have emerged modeling the wet steam and unsteady flow effects, but more work is required in this area to fully understand the impact on the flow structure.

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Section: Swirl Angle Distribution Downstream Of Thementioning

confidence: 98%

A Literature Review of Low Pressure Steam Turbine Exhaust Hood and Diffuser Studies

Burton¹,

Ingram²,

Hogg

2013

Journal of Engineering for Gas Turbines and Power

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“…Collectively, these traces provide a visualization of the recirculation zone. We present flow profiles in the presence and absence of a static mixer since swirling flow has been shown to improve diffuser performance for systems with appreciable separation (McDonald et al, 1971).…”

Section: Angle Of the Diffusermentioning

confidence: 99%

The Caltech Photooxidation Flow Tube Reactor – I: Design and Fluid Dynamics

Huang

Coggon

Zhao

et al. 2016

Preprint

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Abstract. Flow tube reactors are employed to study gas-phase atmospheric chemistry and secondary organic aerosol formation. A new laminar flow tube reactor, the Caltech PhotoOxidation flow Tube (CPOT), has been designed with the aim of achieving a well-characterized fluid dynamic and residence time environment. We present here the design and fluid dynamical characterization of the CPOT, based on the fundamental behavior of vapor molecules and particles in the reactor. The design of the inlet of the CPOT, which was based on computational fluid dynamics (CFD) simulations, comprises a static mixer and a conical diffuser to facilitate rapid development of the characteristic laminar flow parabolic profile. A CFD laminar flow model is developed to simulate the residence time distribution (RTD) of vapor molecules and particles in the CPOT. To assess the extent to which the actual performance adheres to the theoretical CFD model, RTD experiments were conducted with O3 and sub-micrometer ammonium sulfate particles. The measured RTD profiles do not strictly adhere to theory, owing to slightly non-isothermal conditions in the reactor, which lead to secondary flows. Introducing an enhanced eddy-like diffusivity for the vapor molecules and particles in the laminar flow model significantly improves the model-experiment agreement. These characterization experiments, in addition to the idealized computational behavior, provide a basis on which to evaluate the performance of the CPOT as a chemical reactor.

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“…This is particularly true for modern compact discharge cones with rather large cone angle. The benefits of inlet swirl on pressure recovery in conical diffusers has been well documented by Fox et al [17]. As a result, Bovet [16] recommended to leave a small circumferential velocity component when designing the runner, arguing that the losses associated with this excess in outlet kinetic energy is more than compensated by the improvement in the draft tube performance.…”

Section: Introductionmentioning

confidence: 99%

“…Once the axial velocity v z is found by minimizing (16) subject to constraints (17) and (18), the circumferential velocity follows from Eq. (10).…”

Section: Variational Formulation For Swirling Flow At Francis Runner mentioning

confidence: 99%

Analysis and Prevention of Vortex Breakdown in the Simplified Discharge Cone of a Francis Turbine

Susan-Resiga

Muntean

Hasmatuchi

et al. 2010

Journal of Fluids Engineering

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a b s t r a c tWe introduce and validate a novel mathematical model for computing the radial profiles of both axial and circumferential velocity components, respectively, of the swirling flow exiting the runner of hydraulic turbines within the full operating range. We assume an incompressible, inviscid, axisymmetrical, and steady swirling flow, with vanishing radial velocity at runner outlet. First we find the correlation between the flux of moment of momentum downstream the turbine runner and the operating regime given by turbine's discharge and head. Second, we express the relationship between the axial and circumferential velocity components, corresponding to the fixed pitch runner blades, using the swirl-free velocity instead of the traditional relative flow angle at runner outlet. It is shown that the swirl-free velocity profile practically does not change with the operating regime. Third, we introduce a constrained variational problem corresponding to the minimization of the flow force while maintaining the prescribed discharge and flux of moment of momentum. This formulation also accounts for a possible central stagnant region to develop when operating the turbine far from the best efficiency point. Fourth, we show that by representing the unknown axial velocity profile with a suitable Fourier-Bessel series, the discharge constraint can be automatically satisfied. The resulting numerical algorithm is robust and produces results in good agreement with available data for both axial and circumferential velocity profiles measured on a model Francis turbine at several operating regimes. Our mathematical model is suitable for the early optimization stages of the runner design, as it provides the swirling flow configuration at runner outlet without actually computing the runner. By optimizing the parameterized swirl-free velocity profile one can achieve through the inverse design approaches the most suitable runner blades configuration at the trailing edge.

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Effects of swirling inlet flow on pressure recovery in conical diffusers

Cited by 64 publications

References 3 publications

A Literature Review of Low Pressure Steam Turbine Exhaust Hood and Diffuser Studies

A Literature Review of Low Pressure Steam Turbine Exhaust Hood and Diffuser Studies

The Caltech Photooxidation Flow Tube Reactor – I: Design and Fluid Dynamics

Analysis and Prevention of Vortex Breakdown in the Simplified Discharge Cone of a Francis Turbine

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