Reynolds-averaged Navier Stokes Computational Fluid Research Articles

RANS-Based Aerodynamic Shape Optimization of a Wing with a Propeller in Front of the Wingtip

Accounting for propeller–wing interaction allows for the design of more efficient propeller aircraft through strategic propulsion integration. In this paper, the cruise drag of a wing with a propeller located in front of the wingtip is minimized using twist and airfoil-shape design variables. Reynolds-averaged Navier–Stokes computational fluid dynamics with an actuator-disk approach is used for the flow simulations, and a gradient-based algorithm is used for the optimization. Changing the rotation direction of the propeller and optimizing the twist and airfoil shapes of the wing are found to impact the aerodynamic performance significantly, as expected. However, optimizing the wing while accounting for the propeller slipstream during optimization provides little benefit over optimizing it without accounting for the propeller slipstream—a difference of less than one drag count.

Pressure Power Spectra of a ‘Z’ Shaped in Plan Tall Building under Transient Wind Environment

This study foresees the behavior of a ‘Z’ shaped in plan tall building under transient wind storms using unsteady Reynolds-averaged Navier Stokes (URANS) Computational Fluid Dynamics (CFD) technique. Numerical simulations are carried out using ANSYS - CFX, adopting length and velocity scales of 1:300 and 1:5, respectively. Surface streamlines are presented in the article to depict the wind flow characteristics and envisage the regions and nature of flow separations and vortex generations. The flow features also facilitate visualizing the wind pressure contours on building facets. The peak pressure coefficients concerning wind angles of 0° and 90° are presented to enable the cladding design of the building. Moreover, normalized wind pressure power spectra at three different sections along the altitude are offered for 0° to 150° wind at an interval of 30°. It is observed that towards the bottom portion of the building, the peak of the power spectra usually occurs in the low-frequency values. In contrast, at the top and main body of the building, the vortex shedding energy exaggerates at comparatively high reduced frequencies..

Characterization of Out-of-Plane Curved Fluidic Oscillators

A novel fluidic oscillator design, in which the oscillator is curved along the primary flow direction, was evaluated. The effects of mass flow rate, hydraulic diameter, aspect ratio, curvature radius, surface roughness, inlet orientation, and nonconstant curvatures were experimentally investigated. Measurements of the oscillation Strouhal number, discharge coefficient, spreading angle, and sweeping angle were used to characterize the jet. The resulting oscillators were found to fall into one of three categories: oscillated at the same frequency and sweep angle as conventional flat oscillators; oscillated at a slightly higher frequency and lower sweep angle than flat oscillators; or no dominant oscillation frequency detected and with no sweeping action. An unsteady Reynolds-averaged Navier–Stokes computational fluid dynamics simulation revealed fundamental differences in the internal flow mechanisms between flat and curved oscillators that drive the sweeping jet. The curvature between 37.5 and 62.5% of the total length, or the region from the inlet nozzle to halfway through the main chamber, was a primary factor influencing the response type of a design. Due to the curvature of these oscillators, they have the ability to be used in geometrically constrained spaces, such as the leading edge of wings and turbine vanes.

Hypersonic FLEET velocimetry and uncertainty characterization in a tripped boundary layer

Femtosecond laser electronic excitation tagging (FLEET) velocimetry is applied in a hypersonic boundary layer behind an array of turbulence-inducing trips. One-dimensional mean velocity and root-mean-square (RMS) of velocity fluctuation profiles are extracted from FLEET emissions oriented across a 2.75∘ wedge and through a boundary layer above a flat plate in two test campaigns spanning 21 tunnel runs. The experiment was performed in the Texas A&M University Actively Controlled Expansion tunnel that operated near Mach 6.0 with a Reynolds number near 6 × 106 m−1 and a working fluid of air at a density near 2.5 × 10−2 kg m−3. Detailed analysis of random and systematic errors was performed using synthetic curves for error in the mean velocity due to emission decay and the error in the RMS velocity fluctuation due to random error. The boundary layer behind an array of turbulence-inducing trips is documented to show the breakdown of coherent structures. FLEET velocimetry is compared to the tunnel Data Acquisition System, Vibrationally Excited Nitric Oxide Monitoring results, and Reynolds-Averaged Navier–Stokes computational fluid dynamics to verify results.

Aerodynamic Modeling of a Flying Wing Featuring Ludwig Prandtl’s Bell Spanload

This paper presents the aerodynamic modeling of a flying wing featuring Ludwig Prandtl’s bell spanload. The aerodynamic models are developed using a medium fidelity vortex-lattice method and using a Reynolds-Averaged Navier–Stokes computational fluid dynamics solution across a wide range of in-flow angle conditions. A methodology is developed to directly compare the spanwise force distributions from each method. Excellent agreement is seen in the prediction of spanwise inertial aerodynamic forces from each method, as well as in stability and control derivatives dominated by lift and moment contributions. The phenomenon of proverse yaw, caused by the twist distribution necessary to produce the bell spanload, is seen in the high and low-order analysis, with similar off-axis control power predicted.

CFD Analysis of Biofouling Effect on Submarine Resistance and Wake

It is well known that biofouling increases a ship’s resistance and nominal wake. For submarines, any change to the circumferential variation of the nominal wake in the propeller plane will affect the variation of the flow over the propeller blade, and hence the fluctuating forces, and noise, generated by the propeller. The ANSYS FLUENT commercial Reynolds-Averaged Navier Stokes Computational Fluid Dynamics solver was used to investigate the influence of both the longitudinal and vertical distribution of biofouling on the resistance and wake, including the circumferential variation of the nominal wake, on a submarine, using the well-known Suboff standard submarine. For the present work, the k-ε turbulence model was selected, as this is commonly used in this field and is generally considered acceptable. To handle different boundary layer thicknesses in the flow fields, the whole y+ formulation was employed, enabling automatic switching between low and high Reynolds boundary wall models. The numerical solver used for the simulations is based on the finite volume method, which discretizes the RANS equations. In this approach, a segregated model was utilized in the solver, and the convection terms were discretized using the second-order upwind scheme to enhance solution accuracy. The criteria for the near wall are between 30 and 100, and the value of y+ for the present case is 84. It is shown that fouling over only the forward third of the submarine results in a greater increase in resistance than fouling over only the aft third. Fouling over only the lower half of the submarine results in greater resistance than fouling over only the forward third, but less than fouling over the whole of the hull. Fouling over only the forward third of the hull has less influence on the circumferential variation of the wake than fouling over the aft third only of the hull. The results show the importance of keeping the forward area of the hull clean when considering resistance only, whereas keeping the aft area of the hull clean is important when considering the uniformity of the nominal wake into the propeller.

Interaction Mechanism of Transonic Squealer Tip Cooling With the Effect of High-Speed Relative Casing Motion

Abstract The relative casing motion can significantly influence the turbine blade tip aerothermal performance. In this study, experimental investigation was conducted in a newly developed high-speed disk rotor rig which can mimic engine realistic high-speed casing relative motion while enabling full optical access to a transonic turbine blade tip surface. Spatially-resolved tip heat transfer data, including heat transfer coefficient and film cooling effectiveness, were obtained for a cooled transonic squealer tip by infrared transient thermal measurement. Combined with closely coupled Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) analysis, this paper reveals an interesting interaction mechanism between the cooling injections from the pressure side and the cavity floor with and without the effect of relative casing motion. Both experimental data and CFD results show a consistent trend in both heat transfer and cooling performance. With cavity cooling only, the cooling performance reduces with the effect of relative casing motion. However, with additional cooling injection from the pressure side, a significant improvement in the combined cooling performance with the relative casing motion can be observed. Such opposite trend highlights the importance of relative casing motion when ranking different tip cooling designs. With the consideration of relative casing motion, extra tip cooling benefit can be obtained by combining cooling injections from two different locations.

The Effect of a Linear Free Surface Boundary Condition on the Steady-State Wave-Making of Shallowly Submerged Underwater Vehicles

Near-surface simulation methods for shallowly submerged underwater vehicles are necessary for the population of a variety of free-surface-affected, coefficient-based maneuvering and seakeeping models. Simulations vary in complexity and computational costs, often sacrificing accuracy for simplicity and speed. One particular simplifying assumption, the linearization of the free surface boundary conditions, is explored in this study by comparing the steady-state wave-making characteristics of a shallowly submerged prolate spheroid using two different simulation methods at several submergence depths and forward speeds. Hydrodynamic responses are compared between a time-domain boundary element method that makes use of a linearized free surface boundary condition and an inviscid, volume of fluid Reynolds-Averaged Navier–Stokes computational fluid dynamics code that imposes no explicit free surface boundary condition. Differences of up to 22.6%, 32.5%, and 33.3% are found in the prediction of steady state surge force, heave force, and pitch moment, respectively. The largest differences between the two simulation methods arise for motions occurring at small submergences and large wave-making velocities where linear free-surface assumptions become less valid. Nonlinearities that occur in such cases are revealed through physical artifacts such as wave steepening, wave breaking, and high-energy waves. A further examination of near-surface viscous forces reveals that the viscous drag on the vessel is depth dependent due to the changing velocity profile around the body.

Numerical and Experimental Analysis of the Cold Flow Physics of a Nonpremixed Industrial Gas Burner

Abstract The flow field of a nonpremixed industrial gas burner is analyzed with Reynolds-averaged Navier–Stokes computational fluid dynamics validated against velocity and pressure measurements. Combustion is not modeled because the aim is optimizing the predictive capabilities of the cold flow before including chemistry. The system's complex flow physics, affected by a 90 deg turn, backward and forward facing steps, and transversal jets in the mainstream is investigated at full and partial load. The sensitivity of the computed flow field to inflow boundary condition setup, approach for resolving/modeling wall-bounded flows, and turbulence closure is assessed. In the first sensitivity analysis, the inflow boundary condition is prescribed using measured total pressure or measured velocity field. In the second, boundary layers are resolved down to the wall or modeled with wall functions. In the third sensitivity analysis, the turbulence closure uses the k−ω shear stress transport eddy viscosity model or two variants of the Reynolds stress model. The agreement between the predictions of most simulation setups among themselves and with the measurements is good. For a given type of inflow condition and wall flow treatment, the ω-based Reynolds stress model gives the best agreement with measurements among the considered turbulence models at full load. At partial load, the comparison with measured data highlights some scatter in the predictions of different patterns of the flow measurements. Overall, the findings of this study provide insight into the fluid dynamics of industrial gas burners and guidelines for their simulation-based analysis.

High-Fidelity Aerostructural Optimization with a Geometrically Nonlinear Flutter Constraint

When designing aircraft, avoiding dynamic aeroelastic instabilities such as flutter is a key requirement. One way to meet this requirement is to use a multidisciplinary design optimization subject to a flutter constraint. Flutter-constrained design optimizations have used geometrically linear detailed models, which do not accurately predict flutter for very flexible aircraft, or geometrically nonlinear low-order models, which do not accurately trade off cruise range and structural mass. This paper presents a framework for integrating a geometrically nonlinear, subsonic flutter constraint that captures the large in-flight deflections of very flexible aircraft into high-fidelity gradient-based aerostructural optimization. The cruise range and stress constraints are computed accurately with detailed aerostructural analyses, which use a built-up finite element model coupled to Reynolds-averaged Navier–Stokes computational fluid dynamics. The detailed model is condensed to a low-order aeroelastic model to compute the geometrically nonlinear flutter constraint and its adjoint derivatives with computational cost and robustness suitable for optimization. The framework is demonstrated by maximizing the cruise range of a subsonic high-aspect-ratio wing with respect to panel thicknesses, sweep, and span. The impact of the geometrically nonlinear flutter constraint highly depends on the in-flight deformation level. At low deflection levels, sweeping the wing backward is the most effective flutter prevention method, and the flutter constraint has little impact on the achievable cruise range. At high deflection levels, shortening the wing span is necessary to suppress flutter, reducing the achievable cruise range by up to 5.9%. This work is a step toward making multidisciplinary design optimization a practical tool for designing the energy-efficient, very flexible aircraft of the future, which require geometrically nonlinear flutter analyses early in the design cycle to prevent flutter.

Surrogate Model Development for Optimized Blended-Wing-Body Aerodynamics

In the conceptual design phase of conventional-configuration aircraft, calibrated low-fidelity methods provide sufficiently accurate estimates of aerodynamic coefficients. It has been observed, however, that for blended-wing–body aircraft, important flow effects are not captured adequately with low-fidelity aerodynamic tools. Consequently, high-fidelity methods become necessary to study blended-wing–body aerodynamics. Since repeated function calls are needed in an optimization loop, high-fidelity analysis is prohibitively expensive in the conceptual design phase, where several optimization scenarios are considered. In this paper, the integration of high-fidelity data for blended-wing–body aircraft for a mission calculation module is presented. A surrogate model based on Gaussian processes (GPs) with acceptably low prediction error is sought as an alternative to Reynolds-averaged Navier–Stokes computational fluid dynamics. Three adaptations are considered: sparse GPs, mixtures of GP approximators, and need-based filtering for GP. The results provide benchmark values for this case and show that the combination of subsonic and transonic behaviors in the training set is problematic and that, for the considered datasets, sparse GP models suffer from oversmoothing, while mixtures of GP models suffer from overfitting. From the error levels, it is observed that a GP with an infinitely differentiable squared exponential kernel based on reduced data pertinent to mission analysis is the most effective option.

Analytical Model for Ring-Wing Propulsors at Angle of Attack

A simple, accurate, analytical model is developed for predicting the forces and moments on subsonic ring-wing propulsors (aka fan ducts and shrouded propellers) at angle of attack. The method is applicable to drones, aircraft, ships, and more from hover to cruise. The new model is made up from elements of three previously published, closely related models, herein combined and modified for the current purpose: an empty shroud ring-wing force and moment linear aerodynamics model; a ring-wing propulsor axial force model employing linear aerodynamic, axial momentum, and propeller actuator disk theories; and a jet engine normal force model as semi-empirically adapted to ring-wing propulsors. The model’s efficacy is assessed using three independent datasets: two experimental and one Reynolds-averaged Navier–Stokes computational fluid dynamics. It is shown that the model’s algebraic solutions provide good engineering estimates for the lift, drag, normal, and axial forces as well as pitching moments at all operating conditions from hover to cruise and angles of attack up to 85°.

Fluid–Structure Interaction Modeling of Flowfields Within Kevlar-Walled Wind Tunnels

A detailed three-dimensional (3D) two-way coupled fluid–structure interaction simulation of a hybrid anechoic wind tunnel (HAWT) test section is presented with modeling all important effects, namely, turbulence, Kevlar wall porosity, and deflection. The complete 3D flowfield around a 3-ft chord NACA0012 placed into a HAWT test section is assessed. The Kevlar deflections are captured using finite element analysis, whereas 3D Reynolds-averaged Navier–Stokes computational fluid dynamics simulations are used to resolve the flowfield. Source terms are used to model the transpiration flow across the pores of the Kevlar fabric. Results are validated against an extensive experimental dataset. Aerodynamic properties of the airfoil are validated using airfoil pressure coefficients, airfoil wake pressure coefficients, and lift and drag coefficients. Boundary effects are validated against Kevlar wall pressure coefficients, Kevlar displacement, and transpiration velocity through the Kevlar fabric. Overall, a good agreement has been found among all comparisons presented. While some minor discrepancies were observed, these primarily stem from geometrical irregularities of the model and wind tunnel unresolved in the computational fluid dynamics. Overall, the fluid–structure interaction model now enables a detailed assessment of HAWTs to enhance their performance and can support experimental testing.

A High-Speed Disk Rotor Rig Design for Tip Aerothermal Research

Abstract The relative casing motion can greatly vary the over-tip-leakage (OTL) flow structure and aerothermal performance. The existing tip experimental research facilities including stationary linear cascade, cascade rigs with low-speed moving belt, or high-speed rotor rigs are either not capable of reproducing the high relative casing Mach number or extremely expensive and still difficult for optical measurement. This paper presents a high-speed disk rotor design that can simulate the high casing relative speed. The unique feature of this rig design concept is that it enables full optical access of the tip surface under the engine-representative OTL flow condition. In this paper, the feasibility of the design concept is demonstrated and assessed by Reynolds-averaged Navier–Stokes computational fluid dynamics (RANS CFD) simulation, both in component level and in whole rig system level. First-of-its-kind experimental results of spatially resolved tip heat transfer coefficient distribution at high relative casing Mach number are reported. The disk rotor rig design demonstrated in this paper can also be useful for other tip leakage flow studies.

Aerodynamics and Heat Transfer Inside a Gas Turbine Mid-Passage Gap

Abstract Gas turbine blades and vanes are typically manufactured with small clearances between adjacent vane and blade platforms, termed the mid-passage gap. The mid-passage gap reduces turbine efficiency and causes significant additional heat load into the vane platform. This paper presents a new low-order analytical model to quantify the effects of the mid-passage gap on aerodynamics and heat transfer, based only on geometric features and the passage static pressure field. This model is used to calculate losses and heat transfer due to the gap and to derive ideal distributions of purge flow which prevent ingress into the gap. A further simplified estimation method for the effect of gap flow is also presented, so that for any machine the significance of the gap can be quickly assessed based only on geometry and operating conditions. The analysis is validated against both an experimental campaign in a high-speed linear cascade and Reynolds-averaged Navier–Stokes computational fluid dynamics.

Aerothermal Optimization of Turbine Squealer Tip Geometries With Arbitrary Cooling Injection

Abstract The optimization of the turbine rotor tip geometry remains a vital opportunity to create more efficient and durable engines. Balancing the aerodynamic and thermal aspects, while maintaining the mechanical integrity, is key to reshape one of the most vulnerable and life-determining parts of the entire turbine. The ever-increasing turbine gas temperatures, combined with the difficulty of cooling the tip and the aerodynamically penalizing nature of the overtip leakage vortex, make the design of the tip a truly multidisciplinary challenge. While many earlier efforts focused on uncooled geometries or studied the aerothermal impact with a fixed cooling configuration, the current paper presents the outcome of a multi-objective optimization where both the squealer rim geometry and the cooling injection pattern were allowed to vary simultaneously. This study explores a significantly wider design space, seeking a further synergistic aerothermal benefit through the combination of a quasi-fully arbitrary cooling arrangement, with mutating squealer rim structures. Specifically, the current manuscript presents the results of over 330 cooled and uncooled squealer tip geometries. The high-pressure turbine tip was automatically altered using a novel parametrization strategy adopting a maximum of 40 design variables to vary the squealer rim structures, as well as the size and location of the various cooling holes. The aerodynamic and thermal characteristics of every design were evaluated through Reynolds-averaged Navier–Stokes computational fluid dynamics (CFD) simulations with the k–ω shear-stress transport (SST) model for the turbulence closure, adopting an unstructured hexahedral grid typically containing more than 8 × 106 cells. A multi-objective differential evolution algorithm was used to obtain a Pareto front of designs which maximize the aerodynamic efficiency, while minimizing the overtip thermal loads. Eventually, a detailed investigation and robustness study was performed on a set of prime squealer geometries, to further investigate the aerodynamic flow topology and the effect of various cooling injection schemes on the heat transfer patterns.

Propeller Performance at Large Angle of Attack Applicable to Compound Helicopters

An experimental dataset is presented of propeller performance in static condition and at low subsonic airspeeds for various angles of attack up to 90 deg. Numerical investigation through a Reynolds-averaged Navier–Stokes computational fluid dynamics model revealed the mechanisms behind performance changes with advance ratio, angle of attack, and configuration changes. The experimental dataset was found to be free of major errors and is very suitable for validation of propeller models. Furthermore, aerodynamic interaction with an upstream wing was tested with the propeller and wing normal to the flow, to represent the interaction occurring with a time-averaged main rotor slipstream on a compound helicopter. From numerical investigation it was concluded that the results are qualitatively representative of this interaction. The experimental data showed that addition of the wing results in a net reduction of all propeller performance quantities, with thrust reducing up to 20%. Thrust decreasing and thrust increasing mechanisms were found numerically. For most tested operating conditions, the wing resulted in a small decrease of propeller thrust-over-power ratio. Decreasing propeller advance ratio, increasing wing distance, and increasing flap deflection generally decreased the effect of the wing on thrust and power; however, the influence of flap deflection was found to be small.

RANS-Based Aerodynamic Shape Optimization of a Wing Considering Propeller–Wing Interaction

The recent growth of interest in hybrid-electric and fully electric aircraft has led to a renewed focus on the design and optimization of propeller aircraft. Considering propeller–wing interaction provides the opportunity to design aircraft that take advantage of aerodynamic benefits through propulsion integration. In this paper, the cruise drag of a wing with an inboard-mounted tractor propeller is minimized using aerodynamic shape optimization. Reynolds-averaged Navier–Stokes computational fluid dynamics with an actuator-disk approach is used for the simulations, and a gradient-based algorithm is used for the optimization. Changing the rotation direction of the propeller and optimizing the twist and airfoil shapes of the wing impact the aerodynamic performance significantly. However, optimizing the wing while considering the propeller slipstream provides little additional benefit compared to optimizing it without considering the propeller slipstream (the difference is less than one drag count). The wings optimized without considering the propeller slipstream are naturally able to recover swirl almost as effectively as the wings optimized while considering the propeller slipstream, and the propeller-induced velocities for the cruise condition are not high enough to lead to significant airfoil-shape design changes.

Gradient-Based Aerodynamic Optimization of an Airfoil with Morphing Leading and Trailing Edges

This article presents a gradient-based aerodynamic optimization framework and investigates optimum deformations for a transonic airfoil equipped with morphing leading and trailing edges. Specifically, the proposed optimization framework integrates an innovative morphing shape parameterization with a high fidelity Reynolds-averaged Navier–Stokes computational fluid dynamic solver, a hybrid mesh deformation algorithm, and an efficient gradient evaluation method based on continuous adjoint implementation. To achieve a feasible morphing shape, some structural properties of skin and wing-box constraints were introduced into the morphing shape parameterization, which offers skin length control and enables wing-box shape invariance. In this study, the optimum leading and trailing edge deformations with minimization of drag at this cruise stage were searched for using the adjoint-based optimization with a nested feasible morphing procedure, subject to the wing-box, skin length, and airfoil volume constraints. The numerical studies verified the effectiveness of the optimization strategy, and demonstrated the significant aerodynamic performance improvement achieved by using the morphing devices. A lambda shock pattern was observed for the optimized morphing leading edge. That result further indicates the importance of leading edge radius control.

Theoretical study on a novel piezoelectric ocean wave energy harvester driven by oscillating water column

ABSTRACT The wireless sensors offer the possibility of highly accurate salinity, temperature, or pollution detection for the ocean. Therefore, a novel self-powered piezoelectric wave energy harvester with a long service life was developed to replace the batteries in the sensors. A Pb(Zr,Ti)O3(PZT-5A) piezoelectric converter was applied to displace the traditional air turbine in this paper. The wave crest enters the chamber and compresses the entrapped air with oscillating water column (OWC). The outlet of piezoelectric patch deforms and output electric power when it is forced by the fluctuating air pressure. Based on the velocity potential and Green’s function method, theoretical analyses were conducted in the assumption of an incompressible fluid. A numerical OWC aerodynamic model was developed to verify the theoretical calculation based on the Reynolds-Averaged Navier-Stokes equations solver and Computational Fluid Dynamics (CFD) commercial software. The fluctuating air pressure was obtained in the chamber by numerical simulation. The pressure rose to 65 Pa when the ocean wave entered the air chamber with a daft of 0.3 m and a period of 1.8 s. Resultly, the piezoelectric harvester generates electric energy of J. This electric energy was used to evaluate the efficiency piezoelectric wave energy conversion system. Theoretical calculation results were consistent with that of the numerical simulation very well. This work testified their validity for the novel wave energy harvesting system.