Standard and Modified SST Models with the Consideration of the Streamline Curvature for Separated Flow Calculation in a Narrow Channel with a Conical Dimple on the Heated Wall

The testing of the standard and modified SST models of the transfer of shear stresses was carried out on an example of calculating the heat transfer with an intense detached flow around a conical dimple with a slope angle of 45° on the heated wall of a narrow channel. It was shown that the standard turbulence model by Menter SST (MSST) of 2003, widely used in the packages Fluent, CFX, StarCCM+, etc., significantly underestimated the intensity of the return flow. A correction of this model was presented that took into account the influence of the curvature of streamlines within the framework of the Rodi-Leshziner-Isaev (RLI) approach for spatial separated flows. It was found that the predictions for the RLI MSST 2003 were close to the predictions for the original standard MSST 1993, in which the eddy viscosity was calculated using the vorticity modulus. At the same time, the predictions based on the modified one, following Smirnov-Menter (SM) MSST 2003, included in the ANSYS model catalog did not differ too much from the standard MSST 2003. The preference of the MSST modified within the RLI 2003 for calculating the heat transfer in intense separated flows was substantiated.

Numerical modelling of steady detonations with a variational streamline approach

Previous studies (Watt et al. in J Eng Math 75(1):1, 2012; Cartwright and Falle in J Eng Math 115(1):157, 2019) have shown that a streamline based approach to modelling of steady state detonations can produce good results for rate laws which have maximal reaction at the shock. In this paper we consider a Variational Streamline Approximation (VSA) which introduces streamline curvature. Comparing results with Direct Numerical Simulations (DNS) and the existing Straight Streamline Approximation (SSA) model, we find that the VSA improves the predictive accurary of streamlines modelling compared to DNS calculations, capturing the shock front and sonic surfaces with greater accuracy than SSA.

A Rapid Viscous-Inviscid Interaction Method for the Preliminary Design of S-Shaped Transition Ducts

For preliminary design of compressor transition ducts, knowledge-based tools for the rapid assessment of aerodynamic performance of S-shaped ducts are not currently available in the open literature. This is due to the highly complex flow developing under the combined influence of pressure gradients and streamline curvature. This paper presents a new approach enabling an agile design process avoiding premature use of time-consuming high-fidelity CFD calculations. The features of a 2D axisymmetric incompressible steady flow field are captured with a semi-analytical viscous inviscid interaction method. A potential core, based on streamline curvature and implicit velocity profile by parametric spline reconstruction, is coupled to an integral method predicting the turbulent boundary layer growth up to separation. The shear stress distribution is generated by a modified mixing length model for strongly curved flows and wall shear stress closure is performed by inverse calculation of a composite law-of-the-wall. When compared to CFD, the aerodynamic loading is generally predicted to within ±3% but convergence is achieved 20 times faster.

Free Flow and Discharge Characteristics of Trapezoidal-Shaped Weirs

A number of studies have considered the effects of weir design variations on the free- and submerged-flow characteristics of trapezoidal broad-crested weirs. It appears that the hydraulics of short-crested weir flows have received little attention; thus, the current knowledge is incomplete. By systematically analyzing a large set of experimental data, the present study aims to fill in this knowledge gap and to provide a complete description of the discharge characteristics of trapezoidal-shaped weirs, including the salient features of two-dimensional weir flows. The analysis of the axial free-surface profiles for short-crested weir flows attested that the location of the nearest station for the correct measurement of the overflow depth under free-flow conditions is at η0 from the heel of the weir, where η0 is the upstream free-surface elevation. Additionally, an empirical equation for the free-flow discharge coefficient is proposed as being valid for a trapezoidal-shaped weir with varying upstream- and downstream-face slopes. The results of this investigation reveal that the streamline curvature and the slopes of the upstream and downstream weir faces significantly affect the streamwise flow patterns and, hence, the free-flow discharge.

Influence of Swirl Distribution on Blade Shape and Performance of a Centrifugal Impeller

All-over-controlled vortex method is an effective tool to inversely design the 3D impeller of a centrifugal compressor. In this method, swirl distribution is treated as a significant input parameter to control the blade shape, impeller flow field, and compressor performance. It is acknowledged that swirl distribution is prescribed by designers mostly relying on the personal experience at the beginning of design. So how to specify the swirl distribution is still a big challenge for impeller designers. Of the most interest in this paper is to provide a theoretical technique that can be readily applied to specify swirl distribution and reduce the dependence on the designers experience. A judgement criterion rCθ – ωr2 is proposed to design the swirl distribution. Based on the streamline curvature method, a 3D centrifugal impeller design program is developed to design centrifugal impeller. The scale and uniformity of rCθ – ωr2 along flow direction are discussed theoretically to conduct the specifying of swirl distribution. The theoretical analysis is verified by a specific centrifugal compressor case. Then commercial CFD software is used to predict the flow field and the performance of the impeller. The results demonstrate that the scale and distribution uniformity of rCθ – ωr2 have a significant effect on the blade shape and the flow field within the impeller, and possible loss can be reduced. For the new designer, it is possible to preliminarily recognize and eliminate the infeasible swirl distribution, and adjust the unsatisfactory swirl distribution using rCθ – ωr2. Proper blade shape and good impeller performance can be achieved with the help of the judgement criterion rCθ – ωr2.

An Eddy-Viscosity Model Sensitized to Curvature and Wall-Roughness Effects for Reynolds-Averaged Closure

This paper presents a new extension of the realizable K−ε model that accounts for streamline curvature, system rotation, and surface roughness. The model is a type of realizable K−ε model, but the transport equations and the eddy-viscosity damping functions are modified, based on the Richardson number and roughness height; the roughness correction covers both the transitional and fully rough regimes. Flows in a rotating channel and a U-bend duct are used to validate the response of the new model to the system rotation and streamline curvature. The flow in a plane channel and the flow over a dune are used to validate the roughness extension. Finally, a rotating channel with rough walls is studied, to test the new model when both rotation and roughness are present.