Flow Distortion Research Articles

Measurements of Ice Crystal Fluxes from the Surface at a Mountain Top Site

New observations of anomalously high cloud ice crystal concentrations at the Jungfraujoch research station (Switzerland, 3.5 km a.s.l.) are presented. High-resolution measurements of these ice crystals using a high-speed 2D imaging cloud particle spectrometer confirm that the concentrations far exceed those expected from any known primary ice production mechanisms and are at temperatures well below those for known secondary ice production processes to contribute. The most likely explanation is due to a strong surface source generated by the interaction of turbulent deposition of supercooled droplets to fragile ice-covered snow surfaces. This process enhances the detachment of crystal fragments wherein the smaller size mode is turbulently re-suspended even at low wind speeds below expected blowing snow thresholds. These then continue to grow, adding significantly to the ice crystal number concentrations whose size and habit is determined by the transport time between the ice crystal source and measurement location and liquid water profile within the cloud. We confirm, using eddy covariance measurements of ice particle number fluxes, that the likely source is significantly far upwind to preclude flow distortion effects such that the source plume has homogenised by the time they are measured at the mountain top summit.

A Modified Circumferentially Averaged Method for Compressor Performance under Inlet Distortion

Inlet distortion detrimentally affects the aerodynamic performance and lessens the stability of compressors, and has received considerable attention. The need to accurately estimate its effect on the performance and stability of compressor as early as possible in a pre-design cycle is emphasized herein. This work presents a modified circumferential average through flow method (CAM) based on parallel compressor (PC) theory for compressor performance and stability analysis under inlet distortion. The PC approach classically considers independent circumferential flow zones evolving through a compressor, with the same outlet static pressure. In the present work, this theory has been modified in order to create a parametric outlet static pressure boundary condition. It enables us to deal with an upstream flow distortion map, and the meridian plane flow field can then be calculated in order to update the corresponding compressor performance. The model is applied in a compressor which has been tested for its performance characteristics under uniform inlet conditions. Utilizing the new model, the stability and performance of the compressor under inlet distortion can be estimated.

Experimental investigation of the distorted flow field in a new type of direct-connect facility for scramjet studies

A supersonic distorted flow field generated by a new type of direct-connect facility at Mach 2.1 is investigated experimentally via particle image velocimetry (PIV). This facility is designed to accurately reproduce the real flow field in scramjet especially the flow distortion within the isolator, while avoiding the unstart problem in traditional direct-connect facility. The time-averaged velocity fields reveal the principle of flow distortion generated by this facility and show the detailed flow field structures. The mean results suggest that the choose of target parameters distribution will directly affect the performance of this facility. Then, the distorted flow fields in the isolator with a specific non-uniform incoming flow condition are investigated in detail, with the method of proper orthogonal decomposition (POD). The POD analysis of the fluctuating velocity fields finds that there are complex flow field structures within the isolator, including the large-scale vortex structure and the small-scale structure near the wall surface. And these structures in the eigenmodes are associated with the shock wave and the low-velocity region close to the wall surface. Meanwhile, the distorted main flow is also considered to contribute to the flow field instability. Finally, according to the analysis results, the practical guidance of this new type of direct-connect facility is proposed for the subsequent experimental research about scramjet.

A novel approach to reduce fan rotor blades stress in case of resonance due to inlet flow distortion by means of piezoelectric actuators

Resonant vibration condition involves a drop in the life-cycle of the components and is one of the main causes of high cycle fatigue failure (HCF) in turbomachinery blades. As a consequence vibration damping techniques play a key role for turbomachinery designers. Even though resonant vibration conditions can be identified by means of the Singh’s Advanced Frequency Evaluation (SAFE) diagram at the design level, not all resonant conditions can be avoided. Among these methods, systems of piezoelectric (PZT) actuators can be tuned to actively damp the vibrations caused by resonant excitations. In this work, an analytical model was developed to identify the optimal voltage distribution that maximises the reduction in blade stress. The model considers the flexural–torsional–extensional deformations coupling due to the pre-twisting, non-constant cross-section and inertial loads of the rotating blades. A typical case was examined to demonstrate the effectiveness of the proposed method, which involved vibration induced by inlet flow distortion in an axial fan stage coupled with a three-strut front frame. A decoupled approach based on Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) simulations was used to evaluate the aerodynamic loads and to numerically validate the optimal voltage distribution on the PZT actuator pairs. The results show that the proposed method alleviates the effects of the resonant response to an inlet flow distortion on a fan integrally bladed disc (blisk) and the optimal voltage distribution predicted by the model is the one that achieves the highest blade stress mitigation.

An experiment generates a specified mean strained rate turbulent flow: Dynamics of particles

This study aimed to simulate straining turbulent flow empirically, having direct similarities with vast naturally occurring flows and engineering applications. The flow was generated in 100<Reλ<500 and seeded with passive and inertial particles. Lagrangian particle tracking and particle image velocimetry were employed to extract the dynamics of particle statistics and flow features, respectively. The studies for axisymmetric straining turbulent flow reported that the strain rate, flow geometry, and gravity affect particle statistics. To practically investigate mentioned effects in the literature, we present the behavior of both passive and inertial particles from the novel experiment conducted on initially homogeneous turbulence undergoing a sudden axisymmetric expansion. We represent the result with two different mean strains and Reynolds–Taylor microscales. However, this study, in contrast to the previous studies, considers the fields of inertial particles in the presence of gravity. The result discloses that the novel designed and conducted experiments simulated the flow satisfactorily. Then, the particle behavior in such flow showed the effectiveness of the flow distortion on particle dynamics such as velocity root mean square and Reynolds stress. Straining turbulence flow is subject to many industrial applications and physics studies, such as stagnation points, external flow around an airfoil, internal flow in changeable cross section pipe, expansion in the engine mixing chamber, and leading edge erosion. This study's conclusion could apply constructively to these areas.

Effect of Interstage Pipeline on the Performance of Two-Stage Centrifugal Compressors for Automotive Hydrogen Fuel Cells

At present, two-stage centrifugal compressors based on air bearing and high-speed motor technology are widely used in automotive hydrogen fuel cells. The low-pressure stage and high-pressure stage of the compressor are directly connected through an interstage pipeline, thus the structure of the interstage pipeline has an important influence on the aerodynamic performance of the compressor. In this work, a two-stage compressor with three different interstage pipelines were investigated experimentally and numerically. Results show that affected by the interstage pipeline bend section, the flow distortion will be induced at the impeller inlet of the high-pressure stage, and the distortion intensity changes with the pipeline structure. Among the three models, the EPC (elbow pipe change) model induces the most intense total pressure distortion at the condition of 80 kr/min and 130% mass flow rate, resulting in an efficiency reduction of 2 and 1.5 percentage points compared with the SPC (straight pipe change) and the TPC (total pipe change) model, respectively. Further research indicates that the upstream distortion has obvious influence on the downstream rotor blades. As the blade height decreases, the load becomes more uniform on the main blades, while the load extremum migrates to the trailing edge on the splitter blades. Finally, three models are tested, and their performance is compared at three typical rotational speeds., It is recommended that interstage pipelines similar to SPC models should be chosen to improve the two-stage compressor efficiency in the design.

Aerodynamic optimization of the exhaust system of an aft-mounted boundary layer ingestion propulsor

PurposeNovel aircraft propulsion configurations require a greater integration of the propulsive system with the airframe. As a consequence of the closer integration of the propulsive system, higher levels of flow distortion at the fan face are expected. This distortion will propagate through the fan and penalize the system performance. This will also modify the exhaust design requirements. This paper aims to propose a methodology for the aerodynamic optimization of the exhaust for novel embedded propulsive systems. To model the distortion transfer, a low order throughflow fan model is included.Design/methodology/approachAs the case study a 2D axisymmetric aft-mounted annular boundary layer ingestion (BLI) propulsor is used. An automated computational fluid dynamics approach is applied with a parametric definition of the design space. A throughflow body force model for the fan is implemented and validated for 2D axisymmetric and 3D flows. A multi-objective optimization based on evolutionary algorithms is used for the exhaust design.FindingsBy the application of the optimization methodology, a maximum benefit of approximately 0.32% of the total aircraft required thrust was observed by the application of compact exhaust designs. Furthermore, for the embedded system, it is observed that the design of the compact exhaust and the nacelle afterbody have a considerable impact on the aerodynamic performance.Originality/valueThis paper presents a novel approach for the exhaust design of embedded propulsive systems in novel aircraft configurations. To the best of the authors’ knowledge, this is the first detailed optimization of the exhaust system on an annular aft-mounted BLI propulsor.

Effect of cavity pressure on shock train behavior and panel aeroelasticity in an isolator

The flow characteristics of shock train in the isolator play an important role in the overall performance of the scramjet. Although several studies have concentrated on understanding this phenomenon in rigid isolators, few works have focused on methods to control it. The current study proposes a new concept shock train control strategy based on the aeroelastic effect of the flexible panel. An in-house developed code was used to solve the compressible Navier–Stokes equations and the geometric nonlinear equations of the panel, where the conventional serial staggered algorithm was adopted for the two-way fluid–structure interaction. Then, we numerically investigated the effect of cavity pressure on the dynamic behavior of the panel, location, and structure of the shock train, separation zone, and performance of the isolator. The results show that the dynamic response of the panel subjected to the different cavity pressure can be characterized into three states: static stability state, high-frequency second-order limit cycle flutter state, and multi-frequency periodic flutter state. The panel flutter mainly presents an approximately second-mode pattern for the limit cycle flutter state and a first-order vibration mode for the periodic flutter state. With increasing cavity pressure, the average value of shock-train head location moves downstream significantly, while the general trend of separation zone length on top and bottom walls becomes smaller. The flexible panel with the high-frequency second-order limit cycle flutter state can increase the total pressure recovery coefficient with the smaller side load and outlet flow distortion, reduce the averaged separation length, and make the shock-train head move downstream. This is due to the isentropic compression and expansion waves induced by the vibration and deformation of the flexible panel.

Development of Horizontal Vibration-type Synthetic Electric Field Measurement Prototype

At present, field grinding measurement devices are mainly adopted for DC synthetic electric field measurement. The sensor unit of the device is of a rotating blade structure, and the surface wind generated by rotation causes ion flow distortion, making it difficult to ensure the accuracy of measurement data. In order to optimize the sensing structure of measuring equipment, the vibration-type synthetic field sensing mode was obtained through selection analysis, the horizontal vibration sensor structure and data acquisition hardware circuit structure were proposed, and a vibration-type synthetic field measuring prototype was developed. Through the simulation comparison of the influence of vibration type and field grinding type on the electric field, it can be known that the internal field intensity of the upper and lower 1 mm planes of the equipment shell is basically uniform, and the field intensity of the square and the corner position of the equipment shell are distorted. The electric field distortion of the upper surface of the field grinding device and vibration device is 2.36-8.55 and 1.9-6.84, respectively. The higher the device is, the greater the distortion of the field intensity near the shell, and the distortion of the field grinding type is larger than that of the vibration type. Vibration equipment has less influence on the background field intensity when measuring the ground composite field intensity.

The measurement of mean wind, variances, and covariances from an instrumented mobile car in a rural environment

Abstract. On 20 and 22 August 2019, a small tripod was outfitted with a sonic anemometer and placed in a highway shoulder to compare with measurements made on an instrumented car as it traveled past the tripod. The rural measurement site in this investigation was selected so that the instrumented car traveled past many upwind surface obstructions and experienced the occasional passing vehicle. To obtain an accurate mean wind speed and mean wind direction on a moving car, it is necessary to correct for flow distortion and remove the vehicle speed from the measured velocity component parallel to vehicle motion (for straight-line motion). In this study, the velocity variances and turbulent fluxes measured by the car are calculated using two approaches: (1) eddy covariance and (2) wavelet analysis. The results show that wavelet analysis can better resolve low frequency contributions, and this leads to a reduction in the horizontal velocity variances measured on the car, giving a better estimate for some measurement averages when compared to the tripod. A wavelet-based approach to remove the effects of sporadic passing traffic is developed and applied to a measurement period during which a heavy-duty truck passes in the opposite highway lane; removing the times with traffic in this measurement period gives a reduction of approximately 10 % in the turbulent kinetic energy. The vertical velocity variance and vertical turbulent heat flux measured on the car are biased low compared to the tripod. This low bias may be related to a mismatch in the flux footprint of the car versus the tripod or perhaps to rapid flow distortion at the measurement location on the car. When random measurement uncertainty is considered, the vertical momentum flux is found to be consistent with the tripod in the 95 % confidence interval and statistically different than 0 for most measurement periods.

New Concept for Design in Turbomachinery Applications Using Full RANS Gradient Methodology

Abstract Centrifugal compressors are mainly designed with the best efficiency point in mind and the focus oriented toward the impeller. The vaned diffuser geometry is usually developed using simple shapes, such as prismatic blades or wedges, which are unable to account for the flow distortion at the impeller outlet. Investigations of diffuser modifications using computational fluid dynamics (CFD) during the design phase can help to extend the operating range. In order to assess the effect of such modifications, simulations in off-design conditions need to be performed. Accurate predictions of local flow structures at such conditions require a robust flow solver with mixing-plane interfaces and advanced turbulence modeling capabilities. In recent years diffuser modifications were performed mainly based on manual trial-and-error approaches and show considerable potential for improvements. To accelerate the process and allow automation, which is crucial in industrial applications, it is suggested to use an adjoint-based optimization algorithm for diffuser shape design. In this work, a discrete adjoint solver implemented into a robust pressure-based CFD framework was used. While many optimization studies follow the frozen-turbulence approach, which essentially ignores the dependency of the sensitivity on the turbulence quantities, the present adjoint solver fully includes such effects. Automatic differentiation even allows for flexibility with respect to the choice of turbulence model. Any model available in the primal solver can also be used in the adjoint solver. In this particular case, the k–ɛ enhanced wall treatment model was used, since it shows good convergence behavior and is capable of predicting the machine characteristic even at off-design conditions. Mesh morphing was realized via the free-form deformation method, which provides stable mesh deformation and offers a simple and fast setup procedure. Several optimizations were conducted for the RWTH Aachen “Radiver” centrifugal compressor case with vaned diffuser. It was shown that an optimization strategy using a multi-operating point approach, considering part- and overload conditions, is capable of improving the peak efficiency as well as the overall shape of the machine characteristic.

Development of Translucent Design Philosophy for the Cyclic Pattern Design of Fan Outlet Guide Vanes

Abstract The fan systems of typical high bypass civil engines encounter strong flow distortions originating in the intake and the bypass duct. These flow distortions cause the fan stage operation point to vary from its design intent, thus reducing the fan stage performance and increasing low engine-order fan blade forcing. A cyclic pattern design for the fan Outlet Guide Vanes (OGV) can be effectively used to recover the fan stage performance and to control its system-level aeromechanical behavior. This paper presents the development of an OGV pattern design philosophy using the numerical experimentation technique. Multiple fan-intake unsteady computational fluid dynamic computations are conducted by clocking the circumferential pressure profile at the fan exit. The study revealed that a mild, low-harmonic fan back pressure profile with a suitable clocking position is able to improve the fan rotor efficiency and reduce the first engine order (1EO) fan forcing simultaneously. Such a profile can be generated by designing a cyclic OGV pattern that allows the bifurcation potential fields of controlled intensity and phase to pass through the OGV blade row, thus termed the translucent design philosophy. Further, a sensitivity study is performed to assess the effects of simultaneous distortions upstream and downstream of the fan. The study showed that a correctly clocked intra-stage static pressure profile can consistently improve both the performance and aeromechanical behavior of fan systems having different intake lengths and at different flight conditions. The implementation of the proposed translucent design philosophy in a new OGV pattern design tool is discussed.

Numerical Investigation of the Hypersonic Inlet under Throttling with Heat Source

The influence of using a heat source to manage the shock wave boundary layer interactions (SWBLI) at the hypersonic inlet under throttling were studied numerically. This hypersonic inlet was created for a fluid flow Mach number of 5. The throttling was induced by a plug placed near the intake isolator's outlet. The study's parameters included the heat source power and size. The intake performance indicators were the total pressure recovery and the flow distortion. The position of the heat source was determined by studying the interplay of the shock waves from the compression ramp. The results demonstrated the existence of the shock waves at the heat source, and its influences on the SWBLI inside the isolator. This behaviour, led to an increase in the total pressure recovery and reduction of the flow distortion.

Mitigation of Boundary Layer Ingestion Circumferential Distortion Using Nonaxisymmetric Fan Exit Guide Vanes

Abstract This paper presents an assessment of the effect of nonaxisymmetric fan exit guide vanes (FEGVs) to mitigate, or even reduce to zero, the impact of circumferential flow distortion—such as created by boundary layer ingestion (BLI)—on fan rotor efficiency and vibratory structural forcing. The fan response to circumferential nonuniformities is characterized, for two-dimensional flow, in terms of the variations in incidence angle and unsteady rotor forces. FEGV designs with nonaxisymmetric exit flow angle perturbations can eliminate either of these. More importantly, nonaxisymmetric stator row designs can reduce both nonuniformities relative to the influence of an axisymmetric stator row. This suggests that design for distortion need not involve a tradeoff between performance and aeromechanics; a nonaxisymmetric aerodynamic design approach can improve both simultaneously. Analysis of the impact of stage design parameters has been carried out to determine FEGV exit flow angle variations that shield the rotor from the adverse effects of circumferential distortions representative of BLI. The results indicate that inlet distortion effects can be mitigated with realizable nonaxisymmetric FEGVs. The magnitude of the geometry variations required decreases with decreased axial rotor–stator spacing and increased flow coefficient.

Heat transfer and behavior of the Reynolds stress in Mach 6 boundary layer transition induced by first-mode oblique waves

This paper investigates a Mach 6 oblique breakdown via direct numerical simulation in conjunction with stability and quadrant analyses. Particular emphasis is placed on, first, the heat transfer and mean flow distortion in the near-wall and outer transitional boundary layer, and, second, the flow events that are responsible for the production of the Reynolds stress. The energy budget reveals that enhancement of viscous dissipation due to mean flow distortion dominates the heat transfer overshoot, while the dissipation due to fluctuations is lesser but not negligible. Downstream of the location of the peak mean heat flux, the wall temperature gradient (non-dimensionalized by the freestream temperature and local boundary layer thickness) varies little, owing to the occurrence of breakdown and the establishment of self-similarity. Renormalized by the boundary layer thickness, a new correlation of the Stanton number shows no overshoot or difference between the original overshoot region and the turbulent region, which indicates the possibility of similarity once breakdown has occurred. In the outer region, enhanced advective heat exchange strongly reshapes the mean temperature profile. Because of successive modal growth and nonlinear saturation, the contributions of the primary oblique mode, streak mode, and a superharmonic to the outer advective heat transfer are found to compete near the location of the peak heat flux. From the perspective of fluid motions, quadrant analysis highlights the evenly and broadly distributed joint probability density function (PDF) of the fluctuating velocities during transition, which results in overproduction of the Reynolds stress, while the PDF is concentrated around zero in the turbulent region. The flow event Q2 (ejection) overtakes Q4 (sweep) in the outer boundary layer of the transitional region, mainly owing to the primary mode, while the two events become attenuated and nearly achieve balance when transition is complete.

Vorticity amplification in wavy viscoelastic channel flow

Surface distortions to an otherwise planar channel flow introduce vorticity perturbations. In Newtonian fluids, the vorticity induced by small surface undulations on the lower wall is advected by the background flow and diffuses into the fluid. When the fluid is viscoelastic, we identify new mechanisms by which significant vorticity perturbations can be generated in both inertialess and elasto-inertial channel flows. We focus on the case where the lengthscale of the surface distortion is much longer than the channel depth, where we find significant departure from plane shear (Page & Zaki, J. Fluid Mech., vol. 901, 2016, pp. 392–429) due to the non-monotonic base-flow streamwise-normal elastic stress. In inertialess flows, a purely elastic response results in streamlines deforming to match the bottom topography in the lower half the channel. However, the vanishing stress at the centreline introduces a blocking effect, and the associated $O(1)$ jump in normal velocity is balanced by a large-amplitude streamwise-oscillating ‘jet’ in a boundary layer, resulting in a localised, chevron-shaped vorticity perturbation field. In elasto-inertial flows, resonance between the frequency of elasto-inertial ‘Alfvén’ waves and the frequency apparent to an observer moving with the fluid results in vorticity amplification in a pair of critical layers on either side of the channel. The vorticity in both layers is equal in magnitude, to leading order in Weissenberg number, and as such the perturbation vorticity field penetrates the full channel depth even when inertia is dominant. The results demonstrate that long-wave distortions, which are relatively innocuous in Newtonian fluids, can drive a significant flow distortion in viscoelastic fluids for a wide range of parameter values.

Nacelle intake flow separation reduction at cruise condition using active flow control

Turbofan engine intakes are designed to provide separation-free flow at the fan face over a wide range of operating conditions. But at some off-design conditions, like at high flight speeds and high angles of attack (AoA), the aero engine intake may encounter flow separation. This boundary layer separation inside the nacelle inlet of an aircraft engine can lead to a large number of undesirable outcomes like reduction in fan efficiency, engine stall and high levels of stress on the fan blades. Active flow control is a promising solution to reduce inlet boundary layer separation and the associated fan-face flow distortion at such off-design conditions. By blowing pressurized air into the intake near the separation point, the boundary layer is energized and separation can be controlled. This study investigates the applicability of lip blowing, an active flow control technique, to control intake separation and flow distortion at the fan-face. First, intake separation was triggered in a 3D CFD model based on the NASA Common Research Model (CRM) using high AoA cases at cruise condition (Mach number 0.85, Mass flow capture ratio ∼0.7) and the features of separated flow were analyzed. Thereafter, active flow control was introduce to the intake in the form of two types of lip blowing, direct and pitched blowing. The efficacy of lip blowing at achieving separation control in an ultra high bypass ratio turbofan engine intake has been established through this study. The present paper also examines the significance of blowing parameters like the type of blowing, blowing pressure ratio, and blowing slot dimension, at different angles of attack to identify the critical control parameters. Our research successfully establishes proof of concept by demonstrating the feasibility of using lip blowing for separation control in aero-intakes, via numerical modelling. Furthermore, this study also provides crucial insights regarding the important variables to be considered for future experimental studies, and also for detailed studies covering a wider range of operating and blowing conditions.

Design studies on NAGIC flowfield with application to integrated irregular-shaped supersonic inlet

Fighters have increasingly demanding performance on both aerodynamic and stealth. To adapt the design requirement of various irregular-shaped supersonic inlets integrated with flat fuselages, a design method for non-axisymmetric generalized internal conical (NAGIC) flowfield is discussed and then developed. By osculating axisymmetric flow concept and method of characteristics, the developed supersonic NAGIC flowfield can be inversely designed with arbitrary capture curves, controllable incident/terminal shock wave geometries, and post terminal shock wave pressure. Employing the streamline tracing technique, a set of external-compression inward-turning inlets with triangle-like flat capture shapes for supersonic stealth fighters are obtained to verify the design method. The study find that the internal contraction ratio and flow distortion of the inlet are reduced significantly by replacing the weak reflected shock wave in the original hypersonic NAGIC flowfield with a strong one. Thus, the compatibility between inlet and engine is improved in a relatively wide range. In addition, the irregular-shaped curved-compression inlet has high mass ratio and total pressure recovery ratio with negligible cross flow and uniform flow at throat. The performance of inlets with complex configurations can be further improved by matching the entrance geometries of basic flowfields and inlets.

Assessing the Performance of Hypersonic Inlets by Applying a Heat Source with the Throttling Effect

Utilization of a heat source to regulate the shock wave–boundary layer interaction (SWBLI) of hypersonic inlets during throttling was computationally investigated. A plug was installed at the intake isolator’s exit, which caused throttling. The location of the heat source was established by analysing the interaction of the shockwave from the compression ramp and the contact spot of the shockwave with that of the inlet cowl. Shockwave interaction inside the isolator was investigated using steady and transient cases. The present computational work was validated using previous experimental work. The flow distortion (FD) and total pressure recovery (TPR) of the inflows were also studied. We found that varying the size and power of the heat source influenced the shockwaves that originated around it and affected the SWBLI within the isolator. This influenced most of the performance measures. As a result, the TPR increased and the FD decreased when the heat source was applied. Thus, the use of a heat source for flow control was found to influence the performance of hypersonic intakes.

System energy benefit using co-flow jet active separation control for a serpentine duct

Even though active flow control has attracted broad interest to improve flow performance by adding external energy, few studies investigate whether the energy consumed by the AFC can bring energy benefit to the system. This paper numerically demonstrates that co-flow jet (CFJ) active flow control can not only eliminate the flow separation and distortion of a serpentine duct (S-duct), but also leverage the energy state of the inlet system with the available work increased more than the CFJ energy consumed. The 3D Reynolds Averaged Navier-Stokes (RANS) equations with one-equation Spalart-Allmaras turbulence model are used and validated with experiments for the simulation. The optimum configuration of the CFJ S-duct removes the flow separation and virtually eliminates the distortion by reducing DC60 from 41.7% to 0.67%. Benefited from the attached flow, the total pressure recovery is increased by 2.0%. An exergy analysis is conducted to assess the potential benefit of the system available work. A parameter, EIPR, is introduced to measure the merit of an AFC by calculating the ratio of exergy increase to the power required by the AFC. Attributed to the zero-net-mass-flux control, all the power consumed by the CFJ actuators are absorbed by the inlet system as exergy increase. At the same time, the system exergy is further increased by 22% more than the CFJ energy consumption due to removal of flow separation that reduces entropy increase.