3D RANS Research Articles

Suitability of 2D depth-averaged simulations to support predictions of cyprinids passage through Vertical Slot Fishways

Fishways are a key measure to recover longitudinal connectivity. Among them, Vertical Slot Fishways (VSFs) have undergone extensive studies. However, very few numerical studies have included coupled hydrodynamics and ecological simulations. We investigated the impact of using three-dimensional (3D RANS) and two-dimensional (2D SWE) flow simulations in a Eulerian Lagrangian Agent-based Model (ELAM) for VSFs. Spatial distribution of turbulent kinetic energy ( k ), velocity magnitude ( | u i | ) , and velocity strain rate ( S ij ) were evaluated. While the | u i | was consistent across simulations, k was overestimated by the 2D SWE simulations. The frequency of S ij highest values was different between 3D RANS and 2D SWE. Also, the influence of these variables on the agent’s cognitive response was inconsistent. 2D SWE displayed an influence of around 0%, 35%, and 25% for k , | u i | and S ij , respectively. 3D RANS resulted in percentages of around 80% of k , 10–20% of | u i | and 0–10% of S ij . All cases were validated, demonstrating that both approaches are suitable to reproduce experimental observations. We demonstrated that the 2D SWE might serve as a good input to simulate fish movement in VSF. Nonetheless, hydrodynamic variables’ influence on agents’ decision making might be biased from real fish experience.

Uncertainty quantification study of the aerodynamic performance of high-altitude propellers

Performance evaluations for propellers operating at high altitudes are subject to increased uncertainty due to scarce experimental or flight data and difficulties in modeling low Reynolds number flows. For this reason, the Polynomial Chaos Expansion (PCE) method is used in this paper to assess the performance uncertainty of propellers operating at high altitudes. Aleatoric (i.e. linked to the geometry or operating conditions) and epistemic (i.e. linked to the mathematical model describing the flow) uncertainty variables are included in this study to estimate the total uncertainty related to performance predictions made by two physical models, namely 3D RANS with the use of γ−Reθ transition model and Blade Element Momentum Theory (BEMT). In order to validate the proposed method, multipoint uncertainty quantification (UQ) studies are performed for two benchmark propeller geometries under various operating conditions for which experimental data are available. The UQ method is further illustrated on a propeller operating at high altitude. The efficacy of UQ with Computational Fluid Dynamics (CFD) and BEMT is compared and the most influential uncertain variables are found using Sobol's total order indices. As a result of the CFD-based uncertainty quantification studies, two major uncertain variables are identified, providing a direction for more computationally affordable UQ studies.

Flow Feature in Supersonic Non-Isobaric Jet near the Nozzle Edge

Using the example of studying the supersonic underexpanded jet initial section, the issue of interpreting the experimental visualization data and Pitot pressure measurement data using the results of numerical calculations (2d RANS k-ω SST) is discussed. It is shown that the gradient S-shaped feature of the gas-dynamic structure near the nozzle exit, observed in the form of a barrel shock, is a characteristic that separates the expansion and compression regions, and downstream is transformed into a barrel shock. It has been established that the reason for the observed S-shaped curvature of this feature is the axisymmetric nature of the jet flow.

Numerical Study on Natural Ventilation Characteristics of a Partial-Cylinder Opening for One-Sided-Windcatcher of Variable Air-Feeding Orientations in Taif, Saudi Arabia

To provide a clean and cheap source of natural ventilation in windy and arid zones, a windcatcher facility is the best option. This paper aims to study the effect of the inlet opening angle of a new windcatcher model with different values ranging from 60° to 90° for three different feeding orientations at leading-down, central-up, and trailing-down locations. The ventilation performance of the new one-sided windcatcher is numerically examined using CFD simulations, where the 3D RANS and k-epsilon equations are applied at different wind speeds. The flow features of the new models are analyzed and compared with a basic traditional model based on the induced air distribution, aerodynamic losses, and ventilation rates. Results revealed that the sharp edge of the inlet opening leads to an increase in the flow separation and recirculation zone, especially when the opening angle is increased. The highest pressure coefficient is achieved by the trailing-down model compared with the other windcatcher models at an opening angle of 90°. The total pressure drop and ventilation rates increase in all the new windcatcher models due to the increase in the opening angle from 60° to 90°. At identical conditions, with an opening angle of 90° and wind speed of 5 m/s, the trailing-down model achieved a higher pressure coefficient than the leading-down and central-up models by 20.55% and 37.37%, respectively. Furthermore, the trailing-down model could provide higher ventilation rates than the central-up and leading-down models by 31% and 42%, respectively. Finally, the trailing-down windcatcher model can be recommended as the best choice to provide natural ventilation at Taif City in Saudi Arabia.

Improvement of the Parallel Compressor Model and Application to Inlet Flow Distortion

This paper introduces a semi-analytical approach which enables one to deal with distorted inflow in axial fans or compressors. It is inspired by the classical parallel compressor (PC) theory but relies on a local flow-loading coefficient formalism. It is applied to non-uniform flow conditions to study the aerodynamic behavior of a low-speed fan in response to upstream flow distortion. Experimental measurements and 3D RANS simulations are used to evaluate the prediction of fan performance obtained with the local PC method. The comparison proves that, despite its simplicity, the present approach enables to correctly capture first order phenomena, offering interesting perspectives for an early design phase if different fan geometries are to be tested and if the upstream distortion maps are available.

A new simplified numerical approach for shape design of underwater wings

ABSTRACT This paper presents a new simplified numerical approach (SNA) for predicting hydrodynamic data of underwater wings (UWs). Instead of full three-dimensional (3D) flow field analyses, SNA combines Vortex Lattice Method (VLM) and several two-dimensional Reynolds-Average Navier-Stokes (2D RANS) simulations of wing sections to gain results. Hence, SNA shows a remarkably lower computational cost than higher-fidelity methods such as 3D RANS. Moreover, SNA shows good agreements with 3D RANS and experimental data. Thereafter, SNA is applied to shape optimizations of UWs for efficiency and accuracy. Two kinds of optimisation algorithms that include local and global finders are adopted in the optimiser. Searching behaviours of the two algorithms indicate that the problem is not proper to be solved by the local optimiser for its multimodality, while the global optimiser is more efficient. Furthermore, the final optimised wing has few wing-tip vortices and a smooth pressure distribution.

Numerical analysis on the conceptual design of an air-breathing engine inlet working in mach number 3∼5.5

Based on the equal-intensity shock theory, this article designed a supersonic inlet working in Mach number 3.0∼5.5 with the background of an air-breathing engine. The inlet applied the four-shock train mixed compression configuration and inserted a sidewall compression at the beginning of the isolator. Through developing effective 3D RANS computations validated by current experiments, the performance of the designed inlet was identified. The designed inlet self-starts at freestream Mach number Ma∞ = 3.0 under which the total pressure recovery coefficient has dramatic increment, and the aerodynamic choking at the inlet throat no longer presents; the inlet keeps working at all studied flight states with zero angle of attack (AoA) and achieves shock-on-lip at the design point Ma∞ = 5.0. Both positive and negative AoAs can disrupt the equal-intensity shock allocations, which degrade the inlet performance. The inlet obtains maximum total pressure recovery coefficient at zero AoA. The maximum back pressure at Ma∞ = 3.0∼5.5 obtained by the inlet surpasses the requirements and keeps a certain margin. The inlet performance basically meets all the goals proposed by the engine.

The Influence of Mesh Resolution on 3D RANS Flow Simulations in Turbomachinery Flow Parts

The question of the difference mesh refinement degree influence on the results of calculation of the three-dimensional viscous gas flows in the flow parts of turbomachines using the RANS flow models and second order numerical methods is considered. Calculations of flows for a number of turbine and compressor grids on successively refining grids have been performed. We used H-type grids with approximate orthogonalization of cells in the boundary layer. The calculations were carried out using a CFD solver F with the use of an implicit ENO scheme of the second order, a local time step, and a simplified multigrid algorithm. When calculating the flow on fine grids, the following were used: convergence acceleration tools implemented in the solver; truncation of the computational domain with subsequent distribution of the results based on the symmetry property; the computational domain splitting into parts and computations parallelizing. Comparison of the obtained results is carried out, both in terms of qualitative resolution of the complex structure of three-dimensional flows, and in terms of quantitative assessment of losses. Grid convergence was estimated in two ways. In the first, the characteristic two-dimensional distributions of parameters obtained on different grids were visually compared. The purpose of such comparisons was to evaluate the sufficient degree of solution of both the general structure of the flow in grids and its features, namely, shock waves, contact discontinuities, separation zones, wakes, etc. The second estimation method is based on the grid convergence index (GCI). The GCI calculated from the three-dimensional density field was considered in this paper. It is concluded that for scientific research requiring high accuracy of calculations and detailing of the structure of a three-dimensional flow, very fine difference meshes with the number of cells from 106 to 108 in one blade-to-blade channel are needed, while for engineering calculations, under certain conditions, it is sufficient to use meshes with the number of cells less than 1 million in one blade-to-blade channel.

Increase in high-lift devices efficiency of swept wing

The use of Fowler flaps and slotted slats in sweptwing aircraft is the standard solution to increase wing lift at take off and landing. In the literature this solution is known as a classical option of high-lift system of commercial subsonic aircraft. The results of numerical and experimental studies of some solutions intended to increase the efficiency of classical high-lift devices are presented. The concept of the trailing-edge devices called "the adaptive flap" is considered as a way to improve flap efficiency. The adaptive concept is characterized by the integration of spoiler downward deflection to the Fowler flap function. Integration of the spoiler with a movable flap provided an increase of lift in the linear region due to flaps deflected to a higher angle. The steeper upwash angle at a leading-edge device may be the reason of an early stall of the main wing. To protect the leading edge a slotted Kruger flap with streamline form has been used. Preliminary design of classical and improved high-lift systems included the determination of aerodynamic shapes and the optimized position for the high-lift devices. Aerodynamic analysis and design were carried out using 2D RANS Navier-Stokes method. A comparison of computed results has shown visible aerodynamic advantages of an improved high-lift system for maximum lift coefficient and refining the behavior of stall characteristics at high angles of attack. The results of wind tunnel tests of aircraft model with adaptive flap showed its effectiveness.

Numerical simulation of reacting flow in the combustion chamber and study of the impact of turbulent diffusion coefficients

A methodology for combustion modeling with complex mixing and thermodynamic conditions, especially in thrusters, is still under development. The resulting flow and propulsion parameters strongly depend on the models used, especially on the turbulence model as it determines the mixing efficiency. In this paper, the effect of the sigma-type turbulent diffusion coefficients arriving in the diffusion term of the turbulence model is studied. This study was performed using complex modeling, considering the conjugate effect of several physical phenomena such as turbulence, chemical reactions, and radiation heat transfer. To consider the varying turbulent Prandtl, an algebraic model was implemented. An adiabatic steady diffusion Flamelet approach was used to model chemical reactions. The P1 differential model with a WSGG spectral model was used for radiation heat transfer. The gaseous oxygen (GOX) and methane (GCH4) operating thruster developed at the Chair of turbomachinery and Flight propulsion of the Technical University of Munich (TUM) is taken as a test case. The studies use the 3D RANS approach using the 60° sector as the modeling domain. The normalized and absolute pressures, the integral and segment averaged heat flux are compared to numerical results. The wall heat fluxes and pressure distributions show good agreement with the experimental data, while the turbulent diffusion coefficients mostly influence the heat flux.

Performance improvement of axial compressor by introduction of circumferential grooves

ABSTRACT Casing treatment has been extensively used as a prudent passive flow control means to enhance the stall margin with a little decrease in efficiency. The shape of various grooves has a substantial influence on the controlling effect. In this study, research on the impact of rectangular, fillet and chamfer types rectangular grooves with different tip clearances gap on the performance of casing treatment is carried out using numerical simulation. The performance of different models of grooves with different tip clearance gaps on NASA rotor 37 is investigated by discretizing 3D RANS equations based on the finite volume method. A few numbers of casing grooves models are designed with various tip clearances gap and numerically tested. Rectangular circumferential grooves casing treatment (CGCT) shape and smooth wall casing performances are analyzed. Furthermore, the highest adiabatic efficiencies and stall margins of smooth wall casing, rectangular grooves and fillet, and chamfer types rectangular grooves are compared to evaluate the effect of shapes of grooves on the stability and performance of axial flow compressor with different tip gaps. The adiabatic efficiency of the models 1 ~ 6 decreased by 0.9%, 1.0%, 1.05%, 1.1%, 1.2%, and 1.15% respectively. While the stall margin is increased by 4.4%, 2.5 %, 2.2%, 1.75%, 1.7% and 2.1% for models 1 ~ 6 respectively.

3D RANs: 3D Residual Attention Networks for action recognition

In this work, we propose 3D Residual Attention Networks (3D RANs) for action recognition, which can learn spatiotemporal representation from videos. The proposed network consists of attention mechanism and 3D ResNets architecture, and it can capture spatiotemporal information in an end-to-end manner. Specifically, we separately add the attention mechanism along channel and spatial domain to each block of 3D ResNets. For each sliced tensor of an intermediate feature map, we sequentially infer channel and spatial attention maps by channel and spatial attention mechanism submodules in each residual unit block, and the attention maps are multiplied to the input feature map to reweight the key features. We validate our network through extensive experiments in UCF-101, HMDB-51 and Kinetics datasets. Our experiments show that the proposed 3D RANs are superior to the state-of-the-art approaches for action recognition, demonstrating the effectiveness of our networks.

Computational and Experimental Investigations of Ejector Type Actuator Characteristics While Its Using for Flow Control

The general goal of this work is to create the mathematical model of the ejector type actuator, which is installed to the wing model. The second goal of this work is to calculate its characteristics. For this purpose the CFD methods (3D RANS) were used. The experimental data obtained by the authors are used for the mathematical model validation. It is shown that this type actuator is an effective device for the wing flow control at subsonic speeds including landing and take-off regime.

High-lift design for a forward swept natural laminar flow wing

The scope of the paper is to present the results of a RANS-based aerodynamic high-lift design for a natural laminar flow wing with negative sweep. The chosen high-lift system consists of a Krueger leading edge flap with shielding function and a fixed-vane trailing edge flap. The design was first optimized in two main wing sections and then verified by 3D RANS simulations of a wing-body model. Finally, engines were added to the geometric model to estimate the high-lift performance of the landing configuration. With a maximum lift coefficient of $$C_{\text {L}}=2.85$$ for the wing-body model with engine, the target from the preliminary aircraft design was reached. Further potential for improvement was found in the optimization strategy and the shape of the fuselage–wing junction.

CFD analysis of an exceptional cyclist sprint position

A few riders have adopted a rather exceptional and more aerodynamic sprint position where the torso is held low and nearly horizontal and close to the handle bar to reduce the frontal area. The question arises how much aerodynamic benefit can be gained by such a position. This paper presents an aerodynamic analysis of both the regular and the low sprint position in comparison to three more common cycling positions. Computational fluid dynamics simulations are performed with the 3D RANS simulations and the transition SST k–ω model, validated with wind-tunnel measurements. The results are analyzed in terms of frontal area, drag coefficient, drag area, air speed and static pressure distribution, and static pressure coefficient and skin friction coefficient on the cyclist surfaces. It is shown that the drag area for the low sprint position is 24% lower than for the regular position, which renders the former 15% faster than the latter. This 24% improvement is not only the result of the 19% reduction in frontal area, but also caused by a reduction of 7% in drag coefficient due to the changed body position and the related changes in pressure distribution. Evidently, specific training is required to exert large power in the low sprint position.

Study on 2D RANS simulations of underexpanded sonic jets

Study on 2D RANS simulations of underexpanded sonic jets

Flow simulation over a triangular labyrinth side weir in a rectangular channel

Labyrinth side weirs are used as regulator outlets in river diversion structures , water conveyance systems and sewer networks . Herein , the flow around triangular labyrinth side weir with three different included angles (θ = 45 , 60 and 90°) were numerically studied . The 3D RANS equations were solved and VOF method was implemented for free-surface tracking . Different boundary conditions and geometric dimensions were examined and their results were compared with experimental data. Different two-equation turbulence models were implemented. The water depth profiles and overflow discharge were compared with experimental results. The root mean square error of simulated water depth profile using standard k-e model was less than 1 mm. The diverted water discharge was computed with relative error less than 0.7%. The discharge of the labyrinth side weir was 1.7, 1.33 and 1.25 times the discharge of an equivalent normal side weir for θ = 45 , 60 and 90°, respectively.

Investigations of the flow field inside a square cyclone separator using DPIV and CFD

This study used CFD and DPIV to investigate the flow field inside a square cyclone. For CFD, turbulent flow was modelled using 3D RANS equations (with an RSM complementary model). The results of the analysis indicate that the flow inside a square cyclone has two constituents: an outer, free flow and an inner, forced flow in the centre, as with cyclones with the traditional structure. Furthermore, the results indicate that the corners of a square cyclone generate additional vortexes that cause pressure drop to increase (but may, at the same time, potentially improve separation efficiency). The two methods provided highly consistent results. DPIV may be a very good method for validating results obtained with CFD, including for the analysis of flow fields.

Hydrokinetic turbine array modeling for performance analysis and deployment optimization

The promising preliminary results of an ongoing investigation aimed at developing a turbine array optimization tool are presented. This tool uses three-dimensional Reynolds-averaged Navier–Stokes (3D RANS) CFD simulations of free-surface flows to capture blockage effects and turbine-wake interactions present in dense river arrays. Turbines are represented individually into the river model using actuating regions inside which momentum source terms are distributed non-uniformly and scaled with turbine force coefficients (defined with regards to a local velocity scale). These data are derived from a high-fidelity CFD simulation of the specific turbine operating near maximum power extraction.

NUMERICAL STUDY OF DIFFUSER EFFECT ON BLUFF BODY : AERODYNAMIC CHARACTERISTICS

This study focuses on the numerical study of flow structure analysis around bluff bodies close to the downstream face of the free-channel surface. This was investigated using coefficient pressure, coefficient drag, lift coefficient and skin friction coefficient on high Reynolds number (ReH = 2.19 × 106). The general procedure for this research is formulated in detail for allocations in dynamic analysis of fluid computing. The numerical model used is the 2D RANS model (Steady Reynolds Averaged Navier Stokes) with the standard k-ɛ model by giving a flow rate of 40 m / s. This bluff body model will be given the addition of diffuser treatment on the back where the result will be compared to the model without the addition of diffuser and the addition of round shape on the top front on both models. From the research it was found that the coefficient drag bluff body with the addition of diffuser is bigger than the bluff body without the diffuser, it can be concluded that the diffuser angle used is too big causing the coefficient drag to become bigger.