Reynolds-averaged Navier-Stokes Solver Research Articles

Prediction of the Propeller Performance at Different Reynolds Number Regimes with RANS

In this study, a Reynolds averaged Navier-Stokes solver is used for prediction of the propeller performance in open-water conditions at different Reynolds numbers ranging from 104 to 107. The k−ω SST turbulence model and the γ−R˜eθt correlation-based transition model are utilised and results compared for a conventional marine propeller. First, the selection of the turbulence inlet quantities for different flow regimes is discussed. Then, an analysis of the iterative and discretisation errors is made. This work is followed by an investigation of the predicted propeller flow at variable Reynolds numbers. Finally, the propeller scale-effects and the influence of the turbulence and transition models on the performance prediction are discussed. The variation of the flow regime showed an increase in thrust and decrease in torque for increasing Reynolds number. From the comparison between the turbulence model and the transition model, different flow solutions are obtained for the Reynolds numbers between 105 and 106, affecting the scale-effects prediction.

Three-dimensional propulsion characteristics of counter-phase oscillating dual-foil propulsor

A three-dimensional computational study was conducted on the propulsive performance of auto-pitch wing-in-ground effect oscillating foil propulsors (APWIGs) using an unsteady Reynolds Averaged Navier-Stokes solver. This novel propulsor is characterized as the combination of dual-foil configuration and spring-based pitching motion. Both the counter-phase oscillating dual-foil arrangement with produced wing-in-ground (WIG) effect and the auto-pitch mechanism based on attached torsional springs are expected to be favorable for performance improvement. To clearly identify the role of two concerned parameters for APWIGs, the study was divided into two parts of simulations to examine aspect ratio and torsional spring stiffness separately. Firstly, the effect of aspect ratio on the hydrodynamic characteristics was investigated by a fully prescribed oscillating dual-foil configuration. The current computations covering a wide range of aspect ratio from 1 to 10 indicated that the three-dimensional effect tends to dominate the propulsion hydrodynamics with a value of lower than 2. The maximum drop of 14.85% in propulsive efficiency due to the finite-span effect was found at the aspect ratio of 1, while a moderate aspect ratio of 4 leads to an acceptable efficiency loss of 3.22%. Secondly, the three-dimensional hydro-elasticity characteristics of APWIGs as a function of spring stiffness were studied by employing a fixed aspect ratio. A relatively low aspect ratio in which the finite-span effect is still dominant was selected to compare the three-dimensional simulations with two-dimensional predictions. It was observed that the torsional spring stiffness has a significant influence on both hydrodynamic performance and vortex structures of finite-span APWIGs. There exists an optimum spring stiffness for finite-span APWIGs corresponding to the highest efficiency, which resembles the hydro-elasticity characteristics of two-dimensional cases. An averaged efficiency loss of around 10% was reported owing to the low-aspect-ratio effect for three-dimensional APWIGs.

Investigation on aerodynamic performance of wind turbine blades coupled with airfoil and herringbone groove structure

The advantage of wind energy is significant to the improvement of energy structure. This paper is mainly to demonstrate a bionic design for wind turbine blades inspired by the airfoil of owl wing and the herringbone groove structure of owl feathers. The blade of A 200 W horizontal axis wind turbine is taken as prototype blade. The design of bionic airfoil blade is based on 50% and 70% cross section airfoils of owl wing, which is combined with the parameters of the prototype blade. The design of bionic coupling blade is based on bionic airfoil blade, which is coupled with the herringbone groove structure. Numerical simulation is utilized to study the aerodynamic performance of all blades. These simulations utilize an incompressible Reynolds-averaged Navier–Stokes solver and shear stress transport k–ω turbulent model at different tip speed ratios (TSRs). Results show that the power coefficient (Cp) of bionic airfoil blades is higher than that of prototype blade in the TSR of 6–9; the Cp of bionic coupling blades is higher than that of bionic airfoil blades in the TSR of 6–10. The larger curvature of leading edge of blades leads to larger flow velocity, which leads to the smaller pressure on the leeward surface. The herringbone groove structure enhances the flow attachment by generating vortices, which reduces the pressure on the leeward surface of bionic coupling blades. Compared with the prototype blade and bionic airfoil blade, the pressure difference between the windward surface and the leeward surface of the bionic coupling blade is larger.

Coupled Aeroelastic Study of a Flexible Micro Air Vehicle-Scale Flapping Wing in Hovering Flight

Instantaneous force and structural deformation experiments were performed on a flexible, structurally characterized, low-aspect-ratio representative flapping wing. A six-component force balance was used to measure aerodynamic-force time history over a flap cycle. A VICON motion capture setup tracked the wing deformations while flapping. Measured aerodynamic forces and wing deformations were compared against coupled computational fluid dynamics/computational structural dynamics (CFD/CSD) aeroelastic analysis results. The CFD solver is an unsteady Reynolds-averaged Navier–Stokes solver. The CSD solver is a general-purpose multibody dynamics solver capable of modeling geometrically nonlinear beam and shell elements. The CFD/CSD results were able to capture the overall trend in aerodynamic forces and wing deformations. Although predicted and measured variations in lift were similar, the drag-force magnitudes tended to be underpredicted by the coupled aeroelastic solver. The coupled CFD/CSD solver was used to evaluate the influence of wing flexibility on wing performance. Results showed that, in particular instances, decreasing wing stiffness increased the time-averaged aerodynamic lift and lift-to-power ratio. Decreased wing stiffness led to reduced leading-edge vortex circulation strength. This suggests that the increased wing performance is mainly due to a redirection of the resultant force vector allowed by the increased wing compliance.

Validation of transition modeling techniques for a simplified fuselage configuration

A Reynolds-averaged Navier-Stokes solver has been equipped with two different transition prediction and modeling techniques for automatic transition prediction on general three-dimensional geometrical configurations. The first technique is a streamline-based approach that applies an automated local linear stability code, the eN-method and a simplified two-N-factor strategy and is applicable with any kind of turbulence model. The second technique is a transition transport equation approach and uses the γ-Reθ,t model. The standard γ-Reθ,t model has been extended by a modeling approach that captures transition due to crossflow instabilities. The extended model can be applied to three-dimensional configuration exhibiting crossflow transition whereas the original γ-Reθ,t model only captures streamwise transition mechanisms. The paper focuses on a three-dimensional inclined 6:1 prolate spheroid which can be considered as a simplified fuselage configuration. For a number of years this configuration has become a standard basic three-dimensional test case for transition prediction approaches and has been used in a number of international workshops and research activities. The focus of the paper is the validation of the two transition modeling approaches for six different angles of attack using two different turbulence models, a standard two-equation eddy-viscosity model and a differential Reynolds-stress model. The simulation results from the two approaches have been compared against each other and to the available experimental data. The comparisons highlight as many qualitative and quantitative similarities and agreements as they reveal quantitative differences and deviations of specific details.

Assessment of full-scale KCS free running simulation with body-force models

Self-propulsion free running ship simulation is most closely similar to the running ship for different operating condition without any simplification of the ship hull and appendages. Accurate evaluations of self-propulsion performance are vitally important in the design of hull–propeller systems. This paper describes unsteady Reynolds-averaged Navier–Stokes (RANS) simulations to determine the self-propulsion performance of a full-scale container ship with a KP505 propeller. An inhouse code is used to solve the RANS equations with a discretized propeller, descriptive body-force, OUM (Osaka University Method) and modified OUM body-force methods selected as the propulsion models. The modified OUM body-force method couples blade element momentum theory, considering the three-dimensional viscous effects, with the RANS solver. Before the full-scale self-propulsion simulations, uncertainty analyses are performed on the full-scale hull and the propeller. The effect of roughness on the full-scale simulations is also studied. We discuss how the modified OUM body-force method can be used for full-scale self-propulsion simulations, and show that the model-scale body force can be substituted into the full-scale rough propeller in the self-propulsion simulations. The body-force results are compared with extrapolated experimental data, full-scale simulation results from the literature, and simulation results with the discretized propeller. In this paper, the modified OUM shows higher accuracy for full-scale self-propulsion simulation than other two body forces for inhouse URANS solver. Moreover, the scale effect is discussed by comparing open-water, resistance, and self-propulsion simulations at different scales. The open-water and resistance results show that the propeller scale effect can be ignored, whereas both the wake flow and skin friction correction have large scale effects. The self-propulsion scale effect is mainly reflected in the wake factor, thrust deduction factor, and rotation speed. For the container ship considered herein, the full-scale wake fraction is smaller than the model-scale prediction, whereas the rotational speed and thrust deduction factor are greater.

A numerical investigation into the influence of bio-inspired leading-edge tubercles on the hydrodynamic performance of a benchmark ducted propeller

Marine ducted thrusters are widely used to provide propulsive thrust for a range of marine vessels due to their high thrust capability in heavy loaded conditions. This paper presents a novel and optimised bio-inspired marine ducted thruster, where leading-edge tubercles are applied to the duct of a ducted propulsor to explore the impact on hydrodynamic performance. Nine different geometrical configurations of tubercle were investigated with varying amplitude and wavelength within the optimisation study. The hydrodynamic performance of the marine ducted thruster is evaluated using a commercially available computational fluid dynamics (CFD) code, STAR-CCM+, with an incompressible implicit unsteady Reynolds-Averaged Navier Stokes (RANS) solver combined with the Body Force Propeller (BFP) method for the duct optimisation study. Then, the selected optimal duct was chosen for further analysis using the propeller resolved Rigid Body Motion (RBM) method, more commonly known as the sliding mesh technique. Through the numerical optimisation study, the leading-edge modification is predicted to have the capability to enhance the duct thrust in the heavy-loaded conditions, although this is dependent on the wavelength and amplitude of the tubercle. Furthermore, during the investigation the traditional tubercle behaviour was observed, namely the high-low pressure patterns and streamwise counter-rotating vortices. Interestingly, flow separation was observed to be compartmentalised on the outer side of the duct cross-section in conditions where flow separation occurred such as at the maximum efficiency operating point.

Aerodynamic optimization of a luxury cruise ship based on a many-objective optimization system

In the multi-objective optimization discipline (MOD), simultaneous optimization with four or more objectives is referred to as many-objective optimization. Compared with the two-objective and three-objective optimization, many-objective optimization brings a series of new challenges, such as the deterioration of the global search ability of an optimization algorithm, the difficulty of the visualization of Pareto solutions, and the increase of the computational burden. To address these challenges, in this study, an efficient many-objective optimization system was proposed, and this system was utilized to improve the aerodynamics of a Vista-class cruise ship at four crucial wind angles. In the process of design optimization, a parametric model with eight design variables was selected as the initial ship form. The uniform design (UD) sampling technique was employed to design a group of transformed ship forms. The Reynolds-averaged Navier-Stokes (RANS) solver was used to evaluate the aerodynamics of transformed ship forms, and the nearest neighbor mesh (NNM) interpolation method was utilized for the initialization process of each numerical calculation to reduce the computational cost of a single simulation. With the numerical results of all transformed ship forms, four aerodynamic surrogate models were established, using a combined method based on a particle swarm optimization and a radial basis neural network (PSO-RBFNN), to replace large-scale numerical simulation. In addition, the Sobol’ method was introduced to conduct the sensitivity analysis of the design variables. A series of mature genetic algorithms (GAs) were applied for the single-point, two-point, and four-point optimization of the aerodynamics of a cruise ship in sequence. Additionally, the optimal ship form was selected from the Pareto solutions of the four-point optimization based on the quantitative results of the analytical hierarchy process (AHP). Eventually, the dedicated experimental results of the optimized ship form showed that the aerodynamics at the four wind angles were improved together, confirming the effectiveness of the many-objective optimization system.

Influence of position and angulation of a voice prosthesis on the aerodynamics of the pseudo-glottis

The use of a tracheoesophageal valve, also known as voice prosthesis, is currently the most appealing solution for recovering the ability to speak in subjects who have undergone a total laryngectomy. The prosthesis allows the passage of air from the trachea to the esophagus, thereby promoting the flow-induced vibration of the subject’s pharyngoesophageal segment. In turn, the pharyngoesophageal segment modulates the air flow from the lungs into the subject’s vocal tract, acting as an alternative source of acoustic energy to generate voice. The vibration of the pharyngoesophageal segment will likely depend on the aerodynamic forces acting on its wall, which will be defined by the flow characteristics downstream from the valve’s outlet. Previous works have investigated the pressure drop across different prosthesis designs with both in-vitro and in-vivo experiments. Nevertheless, the aerodynamic aspects of the flow in the tracheoesophageal region have only been investigated experimentally in an idealized geometry. This work investigates the influence of the prosthesis position on the aerodynamic behavior of the pharyngoesophageal segment in terms of wall pressure distribution and characteristics of the velocity field. The investigations were carried out with a static model of the tracheoesophageal region based on the finite volume method and a Reynolds-averaged Navier–Stokes solver. The geometry of the system was based on computed tomography images obtained from laryngectomized subjects during phonation at different voice registers and included the geometry of a commercially available voice prosthesis. The results suggest that the position and angulation of the voice prosthesis have a minor influence on the pressure loss along the tracheoesophageal segment and on the pressure distribution on the pharyngoesophageal segment’s wall.

Numerical investigation of three-dimensional partial cavitation in a Venturi geometry

Sheet cavitation appears in many hydraulic applications and can lead to technical issues. Some fundamental outcomes, such as, the complex topology of 3-dimensional cavitation pockets and their associated dynamics need to be carefully visited. In the paper, the dynamics of partial cavitation developing in a 3D Venturi geometry and the interaction with sidewalls are numerically investigated. The simulations are performed using a one-fluid compressible Reynolds-averaged Navier–Stokes solver associated with a nonlinear turbulence model and a void ratio transport equation model. A detailed analysis of this cavitating flow is carried out using innovative tools, such as, spectral proper orthogonal decompositions. Particular attention is paid in the study of 3D effects by comparing the numerical results obtained with sidewalls and periodic conditions. A three-dimensional dynamics of the sheet cavitation, unrelated to the presence of sidewalls, is identified and discussed.

Automatic Transition Prediction in a Navier–Stokes Solver Using Linear Stability Theory

A structured Reynolds-averaged Navier–Stokes solver is directly coupled to a linear stability theory (LST) solver to include the effect of laminar–turbulent transition in the flow simulations. The flowfield variables of the flow solver are used to both find streamlines along which transition can be predicted and to provide the LST code with the required boundary-layer profiles. Instabilities included in the analysis are of the Tollmien–Schlichting and crossflow nature relevant to high-Reynolds-number flows in low turbulence environments. The coupling is fully automated and can therefore be used efficiently in the analysis and design of geometries with external flows. The Technical University of Braunschweig’s sickle wing with spanwise-varying crossflow and the natural laminar flow version of the Common Research Model are simulated under various conditions. Applications to these relevant three-dimensional test cases showcase the capability of the method to model the real flow physics. Advantages and challenges of the approach with regard to future design endeavors are discussed.

Numerical investigation and optimization for interior duct shape of ducted tail rotor

In order to improve the aerodynamic performance of the ducted tail rotor, parametric investigations and optimization of the interior duct surface are performed based on the Computational Fluid Dynamics (CFD) method. Firstly, to predict the aerodynamic characteristics of the ducted tail rotor with high precision and efficiency, the Reynolds-Averaged Navier-Stokes (RANS) solver coupled with body-fitted mesh around rotor blade is established based on the rotating reference frame. Then, novel parametric researches on the aerodynamic characteristics of the ducted tail rotor are conducted with different lip radii, transition section lengths, and duct outlet areas respectively, and the flow separation mechanism on the different interior duct surfaces are obtained. Finally, a new curve lip shape parameterized by the Class Shape Transformation method is employed to replace the conventional circular lip, besides, the transition length and the outlet area which have great influences on the flow separation phenomenon are combined to conduct the optimization of the interior duct surface. Attribute to the suppression of the flow separation, the required power and the FM of the optimized ducted tail rotor show a maximum decrement of 2.49% and a maximum increment of 2.44% with respect to the baseline SA365N1 ducted tail rotor respectively.

Numerical investigation of effect of crossflow transition on rotor blade performance in hover

In the present study, the effect of crossflow transition on the rotor blade performance in hover was investigated numerically. The simulations were conducted for the Pressure Sensitive Paint (PSP) rotor in hover by using a Reynolds-averaged Navier-Stokes (RANS) solver based on unstructured meshes. The k−ωSST model was used for simulating the turbulent flow fields and for calculating the turbulent eddy viscosity. For predicting the laminar-turbulent onset phenomena involving crossflow-induced transition, the γ−Reθt−CF+ transition model was adopted. For the comparison of the transition locations without considering the crossflow transition effect, simulations were also carried out using the γ−Reθt transition model. The calculations were made for the PSP rotor at collective pitch angles from four to 12 degrees with an interval of two degrees. To investigate the effect of blade tip Mach number, two blade tip Mach numbers of 0.585 and 0.65 were tested. The predicted results such as the transition onset location and the rotor aerodynamic performance in terms of thrust coefficient, torque coefficient and figure of merit were compared with experimental data. It was found that proper consideration of the effect of crossflow transition is critical for the accurate prediction of the laminar-turbulent transition onset location on rotor blades. The figure of merit also compares better with the experimental data when the effect of laminar-turbulent transition is included. With the addition of the crossflow transition, the figure of merit is slightly decreased, particularly at low thrust levels.

3-D high-fidelity hydrostructural optimization of cavitation-free composite lifting surfaces

Design and manufacturing technologies have promoted the use of composites in hydrodynamic lifting surfaces. Composites, even with state-of-the-art coatings, are susceptible to cavitation erosion damage. This work aims to design a cavitation-free composite lifting surface to maximize efficiency while ensuring structural integrity. We optimize a canonical hydrofoil using a gradient-based optimization framework that couples a Reynolds-averaged Navier–Stokes solver with a finite-element structural solver. The optimization reduces the weighted drag coefficient by 1.2% over lift coefficients between 0.2 and 0.6, and increases the cavitation inception speed by 82% at the nominal condition compared to the baseline. The optimized design shows higher cavitation inception speeds than an Eppler hydrofoil (E1127, known for cavitation-free operation at moderate lift conditions) with the same baseline planform at CL≥0.2. The improvement from the E1127 hydrofoil was due mostly to delaying tip vortex cavitation induced by 3-D effects. The optimization finds the fiber angle to balance the bend-twist coupling and modifies the directional strength to reduce the susceptibility to excessive deformation and material failure when sweep presents.

A study on ship performance in waves using a RANS solver, part 1: Comparison of power prediction methods in regular waves

Numerical analyses were performed on a KVLCC2 (Korea Research Institute of Ships and Ocean (KRISO) Very Large Crude oil Carrier 2) at Fr = 0.092 and 0.037 in regular wave conditions. A Reynolds averaged Navier-Stokes (RANS) solver was applied with the finite volume method and a realizable k-ε model as a turbulence model. The Volume of Fluid (VOF) equation was solved to implement the free surface. The body-force propeller method of the Virtual Disk model was used to represent the effect of the propeller and reduce the computation time significantly. Resistance and self-propulsion computations were carried out in calm water and regular head waves, and the results were verified by comparing them to the added resistance and motions from experiments. To find the trend of the delivered horsepower (DHP) in regular waves, regular head waves from the short wave to long wave conditions with two different wave steepness were considered. The load variation method was also performed using the obtained added resistance, and the resulting self-propulsion points were compared with the CFD results. In each wave case, the propulsive coefficients and DHP were also compared, and we discuss the relationship between the thrust deduction factor and wake fraction factor according to the wave conditions.

Aerodynamic performance enhancement of co-flow jet airfoil with simple high-lift device

The present study performed a numerical investigation to explore the performance enhancement of a co-flow jet (CFJ) airfoil with simple high-lift device configuration, with a specific goal to examine the feasibility and capability of the proposed configuration for low-speed take-off and landing. Computations have been accomplished by an in-house-programmed Reynolds-averaged Navier-Stokes solver enclosed by k-ω shear stress transport turbulence model. Three crucial geometric parameters, viz., injection slot location, suction slot location and its angle were selected for the sake of revealing their effects on aerodynamic lift, drag, power consumption and equivalent lift-to-drag ratio. Results show that using simple high-lift devices on CFJ airfoil can significantly augment the aerodynamic associated lift and efficiency which evidences the feasibility of CFJ for short take-off and landing with small angle of attack. The injection and suction slot locations are more influential with respect to the aerodynamic performance of CFJ airfoil compared with the suction slot angle. The injection location is preferable to be located in the downstream of the pressure suction peak on leading edge to reduce the power expenditure of the pumping system for a relative higher equivalent lift-to-drag ratio. Another concluded criterion is that the suction slot should be oriented on the trailing edge flap for achieving more aerodynamic gain, meanwhile, carefully selecting this location is crucial in determining the aerodynamic enhancement of CFJ airfoil with deflected flaps.

Numerical analysis of geometrical nonlinear aeroelasticity with CFD/CSD method

Abstract A nonlinear static aeroelastic methodology based on the coupled CFD/CSD approach has been developed to study the geometrical nonlinear aeroelastic behaviors of high-aspect-ratio or multi-material flexible aerial vehicles under aerodynamic loads. The Reynolds-averaged Navier–Stokes solver combined with the three-dimensional finite-element nonlinear solver is used to perform the fluid-structure coupling simulation. The interpolation technique for data transfer between the aerodynamic and structural modules employs radial basis function algorithm as well as dynamic mesh deformation. A high-aspect-ratio structure with multi-material is modeled by the finite element method to investigate the effects of geometrical nonlinearity on the aeroelastic behavior. Numerical simulations of the linear and nonlinear static aeroelasticity were conducted at transonic regime with different angles of attack. By comparing the aeroelastic behaviors of linear and nonlinear structure, it shows that geometrical nonlinearity plays an important role for flexible high-aspect-ratio wings undergoing the large static aeroelastic deformation and should be taken into account in aeroelastic analysis for such structures.

Hydrodynamic Properties of a Moored Floating Breakwater using CFD Approach

In presence of complex-hydrodynamic interaction between water wave and moving structure, a reliable method that can analyse nonlinear phenomena is necessarily required. This paper presents numerical investigation of a moored floating breakwater using computational fluid dynamic (CFD) approach. The mathematical model is based on the extended Reynolds Average Navier-Stokes (RANS) solver for solid-porous obstacle. A high amplitude wave with several wave periods were deliberately considered in the simulation to allow nonlinear wave effects on the floating structure such as wave breaking, overtopping, including viscous friction. Here, the two fluid calculation method for interface boundary between water and air is proposed to capture the complex free surface changes. In addition, the fractional average volume obstacle representation (FAVOR) using partial cell treatment method is employed to simulate the motion of breakwater boundary on the free surface. Approximations and validations on the hydrodynamic properties of the structure have been carried out which include wave transmission coefficient, sway, heave, pitch, and mooring forces. The results show that the CFD model can fairly simulate well on hydrodynamics of the floating breakwater. The discrepancies between numerical and experimental data can be partly attributed to the nonlinearity in the incident wave definition.

Numerical Study on the Tandem Submerged Hydrofoils Using RANS Solver

This paper is presented on the tandem two-dimensional hydrofoils with profiles NACA4412 in single-phase and two-phase flow domains for different submergence depths and different distances in a various angle of attack (AoA). Also, supercavitation is studied at σ = 0.34 by the Zwart cavitation model. Reynolds-averaged Navier–Stokes (RANS) with the shear stress transport (SST) K-ω is employed as a turbulence model in transient analysis of Ansys FLUENT software. The numerical results show that, by increasing depth, the drag coefficient increases for both hydrofoils 1 and 2 as well as the lift coefficient. The drag coefficient of hydrofoil 2 is bigger than hydrofoil 1 for all depths; moreover, it was found that the flow pressure behind the hydrofoil 1 had affected the upper and the lower surface of the hydrofoil 2 at each distance or AoA. These effects are observed in the hydrofoil 2 lift coefficient as well as the flow separation. However, the maximum lift-to-drag ratio is observed at AoA = 8 ° and 3.5c distance. Also, single-phase results reveal that the value of pressure and the hydrodynamic coefficient are very different from the two-phase flow results, due to the elimination of the free surface. So, a two-phase flow domain is recommended for increasing the accuracy of results. In addition, the investigation of supercavitation shows a growth in cavity occurrence on the surface by raising AoA.

Effects of nozzle geometry and active blowing on lift enhancement for upper surface blowing configuration

Upper Surface Blowing (USB) has been regarded as a promising lift enhancement technique for short-take-off and landing (STOL) applications. The present study conducted numerical investigations to further explore the potential capability of USB technique by passive and active flow control strategies. Computations were accomplished by a Reynolds-averaged Navier-Stokes solver enclosed by the two-equation k-ω shear stress transport turbulence model. The propulsion effect of the up-mounted engine was represented by the Turbine Powered Simulator (TPS). Results show that aerodynamic lift of using USB system is significantly enhanced due to the attenuation of plume edge roll-up vortex which is beneficial to the Coanda effect. Varying nozzle geometries can augment lift by alleviating the three-dimensional edge effect and thus delaying the rollup of plume with a thinner jet sheet. Compared to the passive flow control method by nozzle geometry modification, active constant blowing flow control technique shows a more promising potential for lift enhancement for USB powered system. Within the test cases, a 50% lift increment can be achieved by using constant blowing on the USB system.