- United States
Erik Fernandez
Florida State University, College of Engineering, Graduate Student
The objective of this paper is to investigate the material properties of 17-4PH stainless steel printed by the Atomic Diffusion Additive manufacturing technique. Samples with film cooling holes in different orientations were manufactured... more
The objective of this paper is to investigate the material properties of 17-4PH stainless steel printed by the Atomic Diffusion Additive manufacturing technique. Samples with film cooling holes in different orientations were manufactured in a Markforged Metal-X machine. The presence of the holes in these samples helps to understand the printability and accuracy of internal cooling holes, as manufactured by the Metal-X machine. Manufactured samples were first washed to remove the plastic binder. These pre-sintered samples were tested, before sintering, for density, microstructure analysis, CT (Computerized Tomography) scan, roughness, and XRF (X-ray Fluorescence Spectrometer) to understand the material properties. The printed holes, their anomalies, and selection of standards of testing will be discussed along with the material behavior of 17-4PH stainless steel.
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<jats:title>Abstract</jats:title> <jats:p>CFD-based design optimization of turbulent flow scenarios is usually computationally expensive due to requirement of high-fidelity simulations. Previous studies prove that one... more
<jats:title>Abstract</jats:title> <jats:p>CFD-based design optimization of turbulent flow scenarios is usually computationally expensive due to requirement of high-fidelity simulations. Previous studies prove that one way to reduce computational resource usage is to employ Machine Learning/Surrogate Modeling approaches for intelligent sampling of data points in the design space and is also an active area of research, but lacks enough experimental validation. Such a method has been used to optimize the shape of a U-bend channel for the minimization of pressure drop. U-bends are an integral part of serpentine cooling channels inside gas turbine blades but also contribute to total pressure drop by more than 20%. Reducing this pressure loss can help in more efficient cooling at low pumping power. A 'U-bend' or 180-degree bend shape has been used from literature, and a 16-dimensional design space has been created using parametrized spline curves, which creates a variety of shapes inside a given bounding box. A Latin Hypercube Sampling (LHS) was carried out for populating the initial design space with output data from the CFD simulation. After training a surrogate model on this data set, Bayesian updates were used to search for an optimum using an exploration vs exploitation approach. The resulting optimum shape showed that pressure drop was lowered by almost 30%, when compared to the baseline. The aim of this study is to experimentally validate this method using 3D printed models of the baseline and optimum channels respectively. Pressure taps placed across stream-wise locations on these channels helped to create a pressure profile for turbulent flow at a Reynolds number of 17000, for comparison to CFD results.</jats:p>
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The present study aims to understand the flow, turbulence, and heat transfer in a single row narrow impingement channel for gas turbine heat transfer applications. Since the advent of several advanced manufacturing techniques, narrow wall... more
The present study aims to understand the flow, turbulence, and heat transfer in a single row narrow impingement channel for gas turbine heat transfer applications. Since the advent of several advanced manufacturing techniques, narrow wall cooling schemes have become more practical. In this study, the Reynolds number based on jet diameter was ≃15,000, with the jet plate having fixed jet hole diameters and hole spacing. The height of the channel is 3 times the impingement jet diameter. The channel width is 4 times the jet diameter of the impingement hole. The channel configuration was chosen such that the crossflow air is drawn out in the streamwise direction (maximum crossflow configuration). The impinging jets and the wall jets play a substantial role in removing heat in this kind of configuration. Hence, it is important to understand the evolution of flow and heat transfer in a channel of this configuration. The dynamics of flow and heat transfer in a single row narrow impingement ...
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Aerothermal performance of an asymmetrical-profile, leading-edge jet impingement array is studied using numerical and experimental techniques. This array consists of a single row of 9 jets impinging on a leading edge of diameter ratio D/d... more
Aerothermal performance of an asymmetrical-profile, leading-edge jet impingement array is studied using numerical and experimental techniques. This array consists of a single row of 9 jets impinging on a leading edge of diameter ratio D/d = 2, and a distinct suction side/pressure side akin to that of an actual turbine blade. Two different jet-to-target heights are tested, while the jet spacing of 4 jet diameters is kept constant. A range of jet-averaged Reynolds numbers between 20k – 80k are tested. The mean flow field of the mid-jet plane is quantified experimentally, through a non-intrusive experimental method of Particle Image Velocimetry (PIV), while area-averaged heat transfer is measured by the constant temperature copper block technique. The target surface is divided into several copper blocks to investigate the area-averaged heat transfer at each jet. The numerical portion of the presented work serves to investigate the fidelity of the Reynolds Averaged Navier-Stokes (RANS) ...
This investigation focuses on multi-jet impingement configurations for gas turbine geometries in which the objective is to understand the influence of the roughness elements (ribs) on a target surface to the heat transfer and flow field.... more
This investigation focuses on multi-jet impingement configurations for gas turbine geometries in which the objective is to understand the influence of the roughness elements (ribs) on a target surface to the heat transfer and flow field. Existing studies in literature show the implementation of roughness elements for impingement configurations prove to increase heat transfer by 10–30%. Three different surface configurations are chosen for this multi-jet array impingement study: smooth surface (no ribs), small perpendicularly oriented ribs, and large perpendicularly oriented ribs. These roughness elements are non-continuous, broken rib turbulators which are square in cross section and oriented orthogonally to the mean flow direction within the cross flow duct. The roughness elements are oriented perpendicular to the mean flow direction. For each of the ribs tested, the two blockages tested, based on rib-to-channel height, were 20.83% and 41.67%. The jet impingement arrays are of an i...
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Topology optimization uses a variable permeability approach to manipulate flow geometries. Such a method has been employed in the current work to modify the geometric configuration of internal cooling ducts by manipulating the... more
Topology optimization uses a variable permeability approach to manipulate flow geometries. Such a method has been employed in the current work to modify the geometric configuration of internal cooling ducts by manipulating the distribution of material blockage. A modified version of the OpenFOAM solver AdjointShapeOptimizationFOAM has been used to optimize the flow-path of a serpentine channel and high aspect ratio rectangular ducts, with increase in heat transfer and reduction in pressure drop as the objective functions. These duct shapes are typically used as internal cooling channels in gas turbine blades for sustaining the blade material at high inlet temperatures. The serpentine channel shape is initially topologically optimized, the fluid path from which is post-processed and re-simulated in star-ccm+. The end result has an improvement in thermal performance efficiency (η) by 24%. Separation regions are found to be reduced when compared to the original baseline. The second tes...
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Abstract A proof-of-concept study is presented to understand the effect of continuous forcing by a dielectric-barrier-discharge (DBD) plasma actuator on the strength of the vortices formed in the tip-gap of a single NACA0065 airfoil. The... more
Abstract A proof-of-concept study is presented to understand the effect of continuous forcing by a dielectric-barrier-discharge (DBD) plasma actuator on the strength of the vortices formed in the tip-gap of a single NACA0065 airfoil. The airfoil was mounted with variable tip gaps in the test-section of a suction-type wind tunnel. Continuous forcing was generated by mounting a straight DBD actuator in the tip gap. The flow field was investigated experimentally by dynamic-pressure measurements, and stereoscopic-particle-image-velocimetry (SPIV). In addition, URANS was performed to investigate the flow field in the tip gap region, where SPIV could not be conducted. The results showed that the effectiveness of forcing decreased with increasing tip-gaps and free-stream velocity. The maximum cancellation of the vortex was observed when the blowing ratio was approximately 0.93, with a tip gap of 0.02c ( c = chord ) and free stream velocity of 2.7 m/s. Both experimental and numerical results showed that in this particular case, the DBD actuator created a strong reverse flow opposing the direction of tip flow. This reverse flow altered the pressure gradient in the tip gap region and canceled the vortex altogether.
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Serpentine channels are a common feature seen in heat exchanger geometries. For example, they are present in midchord regions of gas turbine blades to prevent material failure at high turbine inlet temperatures. Due to their serpentine... more
Serpentine channels are a common feature seen in heat exchanger geometries. For example, they are present in midchord regions of gas turbine blades to prevent material failure at high turbine inlet temperatures. Due to their serpentine nature, these channels contain 180 degree turns or Ubends. These Ubends are responsible for nearly 20% of the pressure drop in such channels. A topology optimization method has been used in the current study to optimize the shape of a baseline Ubend for minimum pressure drop, at a Reynolds number of 17,000. TO uses a variable permeability approach to design an optimum flow-path by manipulation of solid blockage distribution in the flow path. The pressure drop across the channel was lowered by 50% when compared to a standard Ubend channel profile from literature. Postprocessing was performed to extract the flow-path and run a forward simulation in STAR-CCM+ after remeshing with wall refinement. A 3D printed model of the TO shape and benchmark Ubend was...
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The present study aims to understand the flow, turbulence, and heat transfer in a single row narrow impingement channel for gas turbine heat transfer applications. Since the advent of several advanced manufacturing techniques, narrow wall... more
The present study aims to understand the flow, turbulence, and heat transfer in a single row narrow impingement channel for gas turbine heat transfer applications. Since the advent of several advanced manufacturing techniques, narrow wall cooling schemes have become more practical. In this study, the Reynolds number based on jet diameter was ≃15,000, with the jet plate having fixed jet hole diameters and hole spacing. The height of the channel is three times the impingement jet diameter. The channel width is four times the jet diameter of the impingement hole. The dynamics of flow and heat transfer in a single row narrow impingement channel are experimentally and numerically investigated. Particle image velocimetry (PIV) was used to reveal the detailed information of flow phenomena. PIV measurements were taken at a plane normal to the target wall along the jet centerline. The mean velocity field and the turbulent statistics generated from the mean flow field were analyzed. The exper...
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The research presented in this paper strives to exploit the benefits of near-wall measurement capabilities using hotwire anemometry and flowfield measurement capabilities using particle image velocimetry (PIV) for analysis of the... more
The research presented in this paper strives to exploit the benefits of near-wall measurement capabilities using hotwire anemometry and flowfield measurement capabilities using particle image velocimetry (PIV) for analysis of the injection of a staggered array of film cooling jets into a turbulent cross-flow. It also serves to give insight into the turbulence generation, jet structure, and flow physics pertaining to film cooling for various flow conditions. Such information and analysis will be applied to both cylindrical and diffuser shaped holes, to further understand the impacts manifesting from hole geometry. Spatially resolved PIV measurements were taken at the array centerline of the holes and detailed temporally resolved hotwire velocity and turbulence measurements were taken at the trailing edge of each row of jets in the array centerline corresponding to the PIV measurement plane. Flowfields of jets emanating from eight staggered rows, of both cylindrical and diffuser shape...
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An experimental investigation was carried out with an objective to enhance the flight envelop of a generic USA-35B wing at low speeds. The technique employed in this study is a pair of longitudinal ridges to take advantage of both leading... more
An experimental investigation was carried out with an objective to enhance the flight envelop of a generic USA-35B wing at low speeds. The technique employed in this study is a pair of longitudinal ridges to take advantage of both leading edge protrusions and chordwise fences. Two-component particle image velocimetry (PIV) was used to measure the velocity field. In the present study, the ridge height and inter-ridge spacing were varied to obtain an optimal control configuration for maximum effectiveness in terms of flow separation region and attachment location. The results showed that the baseline airfoil exhibited a massive flow separation on the suction side at an angle of incidence of 12° and beyond. With the addition of optimal longitudinal ridges, the stall was significantly delayed and the flow was completely attached on the entire airfoil surface up to an angle of incidence of 16°. The study suggest that longitudinal ridges are simple in design, implementation and very effective for separation con...
Research Interests: Geology and Flow Control
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Abstract Active flow control is applied to the Honda Simplified Body (HSB), a flat-back ground vehicle model, for aerodynamic drag reduction. The use of small scale, steady jets (microjets) in normal and tangential injection orientations... more
Abstract Active flow control is applied to the Honda Simplified Body (HSB), a flat-back ground vehicle model, for aerodynamic drag reduction. The use of small scale, steady jets (microjets) in normal and tangential injection orientations is investigated through experimental parametric studies and companion numerical simulations. Parameters such as injection location relative to separation point, jet diameter, and blowing ratio are explored. The flow response is characterized experimentally by aerodynamic force measurements and velocity field measurements. The computational effort utilizes Large Eddy Simulation (LES) to uncover how flow control with a steady microjet array modifies the wake and the corresponding drag. The impact of the microjets on the baseline flow field is discussed. The computational study introduces the actuator array on the top surface of the model body to support the experimental study that examines the effectiveness of flow control with microjets installed on multiple side surfaces. From both experimental and numerical analyses, it is observed that the wake can be modified with microjets such that the drag experienced by the HSB is reduced by nearly 3% with net reduction in power consumption.
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The effect of lateral jet-to-jet spacing in a microjet array has been examined in the context of a separation flow control application. The main mechanism responsible for separated flow reattachment from microjet actuation is the... more
The effect of lateral jet-to-jet spacing in a microjet array has been examined in the context of a separation flow control application. The main mechanism responsible for separated flow reattachment from microjet actuation is the generation of streamwise vorticity due to the counter rotating vortex pair (CRVP) produced by the jet in cross-flow. These CRVPs entrain high momentum freestream fluid to the near wall regions, thus energizing the low momentum boundary layer. As the jet-to-jet spacing changes, the interaction between streamwise vortices and their impact on flow control effectiveness must be examined. Three microjet arrays with 6.25, 12.5, and 25 diameter spacings are investigated. Steady Reynolds Averaged Navier-Stokes (RANS) simulations modeling the microjets in a zero pressure gradient cross-flow, were performed for the three jet spacings. 12.5d and 25d spacing simulations revealed the presence of coherent streamwise vortices past 80 jet diameters. The 6.25d spacing however, is characterized by a rapid decay of streamwise vorticity downstream of injection with coherent vortices lasting only about 20 jet diameters downstream. This is attributed to enhanced interaction of CRVPs generated by adjacent microjets and, due to their close proximity, their rapid dissipation. This configuration is also characterized by a stretching of streamwise vorticity in the wall normal direction. Experimentally, a highly adverse pressure gradient was imposed on a flat plate for the same three microjet spacings. The effectiveness of each confinguation was examined for controlling the characteristic flow separation. Pressure distributions measured along the flat plate centerline demonstrate that each configuration (corresponding to three microjet spacings) was able to effectively reattach the separated flow. A jet to cross-flow velocity ratio of 10 was found to be effective for all three cases. Similarly, a steady momentum coefficient of about 0.7 was also found to be effective for all three cases. The analysis further reveals that the 25d microjet configuration was the most efficient for this particular application in that it produced the greatest benefit at minimal cost in terms of actuator mass flow rate. Velocity fields measured through Particle Image Velocimetry for the selected optimal control cases reinforced the results from the surface pressure distributions and simulations. As seen in the numerical results, the 6.25d jet configuration showed a substantial velocity deficit downstream of the injection location compared to the larger jet spacing configurations.
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Jet to crossflow velocity ratio and lateral jet-to-jet spacing are two important parameters which have a direct impact on separation control efficacy for fluidic jet in crossflow actuators (JICF). The influence these parameters have on... more
Jet to crossflow velocity ratio and lateral jet-to-jet spacing are two important parameters which have a direct impact on separation control efficacy for fluidic jet in crossflow actuators (JICF). The influence these parameters have on the control of a separated flow field have been examined in this study. Two component Particle Image Velocimetry (PIV) and three component Stereo PIV techniques have been used to measure the global streamwise velocity field and cross plane velocity fields near the microjet injection location, respectively. Three microjet array configurations were evaluated; 6.25, 12.5, and 25 diameter jet-to-jet spacings. Jet velocity to crossflow velocity ratios of 2, 5, and 10 were examined at each array configuration. A highly adverse pressure gradient imposed on a flat plate provided a suitable flow field for examining actuator effectiveness (Reynolds number = 46,400 (1.47 m/s)). The smallest jet-to-jet spacing of 6.25d is characterized by high levels of Turbulent Kinetic Energy (TKE) just downstream of injection accompanied by a rapid loss of coherent streamwise vortices. As the jet-to-jet spacing increases, mutual vortex interaction decreases and coherent streamwise vortices can be identified further downstream of injection. A drop in TKE levels is also seen as jet spacing increases due to decreased jet-to-jet interaction. Jet to velocity ratios of 2 and 10 are effective in drastically reducing or eliminating the separation bubble while a velocity ratio of 5 is the least effective. Two different mechanisms for boundary layer re-energization are seen; momentum transfer from large scale counter-rotating vortices (CVPs) and momentum flux through turbulent transport. Although both of these mechanisms are present for all blowing configurations, one is more dominant depending on the spatial actuator configuration or jet to crossflow velocity ratio.
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A pair of longitudinal ridges is employed to enhance the aerodynamic efficiency of an USA-35B airfoil used in a remotely controlled aircraft wing. Measurements include surface static pressure distributions, 2-dimensional and stereo... more
A pair of longitudinal ridges is employed to enhance the aerodynamic efficiency of an USA-35B airfoil used in a remotely controlled aircraft wing. Measurements include surface static pressure distributions, 2-dimensional and stereo particle image velocimetry. In the present study, the height and inter-ridge spacing were varied to find optimal control configuration for maximum effectiveness. The results show that the baseline airfoil exhibits a massive flow separation on the suction side at an angle of incidence of 12 and beyond. With the addition of optimal longitudinal ridges, the stall angle was significantly delayed and the flow was completely attached up to an angle of incidence of 16. These results clearly show the benefit of using longitudinal ridges as an effective flow control technique for improving aerodynamic characteristics of an aircraft wing.
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A high fidelity LES Navier-Stokes solver was utilized to investigate and understand vortex asymmetry phenomenon on a 12 semi-apex angle cone at Reynolds number of 100,000 and freestream Mach number of 0.3. Flow field characteristics are... more
A high fidelity LES Navier-Stokes solver was utilized to investigate and understand vortex asymmetry phenomenon on a 12 semi-apex angle cone at Reynolds number of 100,000 and freestream Mach number of 0.3. Flow field characteristics are assessed with the introduction of multiple random imperfections near the tip of the conical body. Results show symmetrical flow features at α = 20° and asymmetrical flow pattern at α = 40°. The magnitude of asymmetry varies with roll orientation of the nose cone.
A macro fiber piezoelectric composite has been deve loped for boundary layer management of Micro-Air Vehicles (MAVs). Specifical ly, a piezoelectric composite that is capable of self-sensing and controlling flow has been model e ,... more
A macro fiber piezoelectric composite has been deve loped for boundary layer management of Micro-Air Vehicles (MAVs). Specifical ly, a piezoelectric composite that is capable of self-sensing and controlling flow has been model e , designed, fabricated, and tested in wind tunnel studies to quantify performance characterist ics, such as the velocity field response to actuation, which is relevant for actively managing boundary layers (laminar and transition flow control). A nonlinear piezoelectric plate model wa s utilized to design the active structure for flow control. The dynamic properties of the piezoe lectric composite actuator were also evaluated in-situ during wind tunnel experiments to quantify sensing performance. Results based on velocity field measurements and unsteady pressure measuremen ts show that these piezoelectric macro fiber composites can sense the state of flow above the su rface and provide sufficient control authority to manipulate the flow conditions for transition from laminar to turbulent flow.
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An experimental investigation of detailed flow and heat transfer in a narrow impingement channel was studied; the channel included 15 inline jets in a single row with a jet-to-target wall distance of 3 jet diameters. The spanwise length... more
An experimental investigation of detailed flow and heat transfer in a narrow impingement channel was studied; the channel included 15 inline jets in a single row with a jet-to-target wall distance of 3 jet diameters. The spanwise length of the channel was 4 jet diameters, and a streamwise jet spacing of 5 jet diameters was considered for the current study. Both the flow physics and heat transfer tests were run at an average jet Reynolds number of 30,000. Temperature sensitive paint was used to study heat transfer at the target wall. Along with other parameters, jet-to-jet interaction in a narrow row impingement channel plays a significant role on heat transfer distribution at the side and target walls as the self-induced jet cross flow tends to bend the downstream jets. The present work shows detailed information of flow physics using Particle Image Velocimetry (PIV). PIV measurements were taken at planes normal to the target wall along the jet centerline for several jets. The flow ...
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A macrofiber piezoelectric composite has been developed for boundary layer management of micro-air vehicles (MAVs). Specifically, a piezoelectric composite that is capable of self-sensing and controlling flow has been modeled, designed,... more
A macrofiber piezoelectric composite has been developed for boundary layer management of micro-air vehicles (MAVs). Specifically, a piezoelectric composite that is capable of self-sensing and controlling flow has been modeled, designed, fabricated, and tested in wind tunnel studies to quantify performance characteristics, such as the velocity field response to actuation, which is relevant for actively managing boundary layers (laminar and transition flow control). A nonlinear piezoelectric plate model was utilized to design the active structure for flow control. The dynamic properties of the piezoelectric composite actuator were also evaluated in situ during wind tunnel experiments to quantify sensing performance. Results based on velocity field measurements and unsteady pressure measurements show that these piezoelectric macrofiber composites can sense the state of flow above the surface and provide sufficient control authority to manipulate the flow conditions for transition from laminar to turbulent flow.
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ABSTRACT Flow separation that occurs over low-pressure turbine blades at low Reynolds numbers has been a cause of concern due to its detrimental effect on engine performance. In the present study, the effect of microjet actuation, a... more
ABSTRACT Flow separation that occurs over low-pressure turbine blades at low Reynolds numbers has been a cause of concern due to its detrimental effect on engine performance. In the present study, the effect of microjet actuation, a low-mass, high-momentum device, is demonstrated for the elimination of separation on a low-pressure turbine blade over a wide range of Reynolds numbers using a range of complementary diagnostics, which include the surface pressure, velocity field, and wake-loss measurements. The U.S. Air Force Research Laboratory L1A low-pressure turbine blade used in this study is a highly aftloaded profile that experiences a nonreattaching separation at approximately 60% axial chord at low Reynolds numbers. Baseline blade pressure distributions as well as wake-loss coefficient measurements show that the blade experiences nonreattaching separation for Reynolds numbers based on axial chord less than 50,000 for a freestream turbulence intensity of 1% with steady inlet conditions. Microjet-based control was activated at various blowing ratios for each Reynolds number of interest. The integrated wake-loss coefficient was reduced by 85% with microjet control at low Reynolds numbers. Ensemble-averaged particle image velocimetry velocity fields show an elimination of reverse flow on the blade&#39;s suction surface when steady microjets were activated at the optimum blowing ratio during low Reynolds number conditions. Turbulence statistics found through particle image velocimetry showed a concomitant dramatic reduction in unsteady velocities with control. Boundary-layer reattachment is attributed to the increase of local streamwise vorticity caused by the microjets (jets in crossflow), which lead to enhanced freestream entrainment to the near wall. The boundary layer is further energized due to enhanced turbulent mixing far downstream of the microjets. It was also observed that excessive control at high blowing ratios actually leads to a much larger separation. Prior studies applying active control on low-pressure turbines have shown the effectiveness of pitched and skewed vortex-generating jets for eliminating flow separation. The current study demonstrates that simple, normally issuing microjets with zero pitch angles and very low mass flow can be as effective as vortex-generating jet actuators for low-pressure turbine flow control.