VTechWorks Repository :: Browsing by Author "Dancey, Clinton L."

Browsing by Author "Dancey, Clinton L."

Now showing 1 - 20 of 158

3-D flow and performance of a rocket pump inducer at design and off-design flow rates
Doan, Andrew W. (Virginia Tech, 1994-08-05)
The ADP rocket pump inducer was studied computationally using a 3-D Navier-Stokes solver, The Moore Elliptic Flow Program. Design and off-design flow rates were simulated to qualitatively and quantitatively study the effects of flow rate on the flow and performance. Several views of the results were created to aid flow visualization. The 3-D laser measurements made by Rocketdyne were used for comparison. The velocity magnitudes as well as the flow patterns within the inducer match well between the calculated and measured results. The axial velocity distribution and the rotary stagnation pressure, losses, are predicted very well by the calculation. The internal flow patterns developed in the simulation as expected, with radial outflow in the blade boundary layers. The tip leakage flow formed a recirculation region, a toroidal shaped vortex at the tip leading edge of the blades. The associated backflow forms a blockage that varies with flow rate. The thermodynamic performance was evaluated by calculating the contributions to pressure rise, the pump characteristic, the contributions to moment of momentum, and the efficiency. The centrifugal effect and relative velocity effect were found to vary with flow rate. The effective inlet throat radius, which governs these two effects, changes with flow rate because of the recirculation blockage. The shear on the blades was found to produce a small fraction of the work in the inducer, and most was produced by the pressure difference across the blade. The inducer efficiency was about 89%, and increased with decreasing flow rate in the range of flow rates considered, from 89% to 110% of the design flow rate.
Aerodynamic Force and Pressure Loss Measurements on Low Aspect Ratio Pin Fin Arrays
Thrift, Alan Albright (Virginia Tech, 2007-02-09)
The desire to achieve higher heat transfer augmentation for turbine blades is fueled by the increased power output and efficiency that is achievable with high turbine inlet temperatures. The use of internal cooling channels fitted with pin fin arrays serves as one method of accomplishing this goal. Consequently, the addition of pin fin arrays comes at the expense of increased pressure drop. Therefore the pin fin geometry must be judiciously chosen to achieve the required heat transfer rate while minimizing the associated pressure drop. This project culminates in the measurement of both pin fin force and array pressure drop as they related to changes in the array geometry. Specifically, the effects of Reynolds number, spanwise pin spacing, streamwise pin spacing, pin aspect ratio, and flow incidence angle. Direct two-component force measurement is achieved with a cantilever beam force sensor that uses highly sensitive piezoresistive strain gauges, relating the strain at the base of the beam to the applied force. With proper characterization, forces as small as one-tenth the weight of a paper clip are successfully measured. Additionally, array pressure drop measurements are achieved using static pressure taps. Experiments were conducted over a range of Reynolds numbers between 7,500 and 35,000. Changes in the spanwise pin spacing were shown to substantially alter the pin fin drag and array pressure drop, while changes in the streamwise pin spacing were less influential. The experimental results also showed a dramatic reduction in the pin fin drag and array pressure drop for an inline flow incidence angle. Finally, changes in the pin aspect ratio were shown to have little effect on the array pressure drop.
Aerodynamic Performance of a Flow Controlled Compressor Stator Using an Imbedded Ejector Pump
Carter, Casey Joseph (Virginia Tech, 2001-02-09)
A high-turning compressor stator with a unique flow control design was developed and tested. Both boundary layer suction and trailing edge blowing developed from a single supplied motive pressure source are employed on the stator. Massflow removed through boundary layer suction is added to the motive massflow, and the resulting combined flow is used for trailing edge blowing to reduce the total pressure deficit generated by the stator wake. The effectiveness of the flow control design was investigated experimentally by measuring the reduction in the total pressure loss coefficient. The experiment was conducted in a linear transonic blowdown cascade wind tunnel. The inlet Mach number for all tests was 0.79, with a Reynolds number based on stator chordlength of 2,000,000. A range of inlet cascade angles was tested to identify the useful range of the flow control design. The effect of different supply massflows represented as a percentage of the passage throughflow was also documented. Significant reductions in the total pressure loss coefficient were accomplished with flow control at low cascade angles. A maximum reduction of 65% in the baseline (no flow control) loss coefficient was achieved by using a motive massflow of 1.6% of the passage throughflow, at cascade angle of 0°. The corresponding suction and blowing massflow ratio was approximately 1:3.6. Cascade angle results near 0° showed significant reductions in the loss coefficient, while increases in the cascade angle diminished the effects of flow control. Considerable suction side separation and the presence of a leading edge shock are noticeable as the cascade angle is increased, and contribute to the losses across the stator surface. Also identified was the estimated increase in wake turning due to flow control of up to 4.5°.
Analysis Methods to Control Performance Variability and Costs in Turbine Engine Manufacturing
Sheldon, Karl Edward (Virginia Tech, 2001-05-04)
Few aircraft engine manufacturers are able to consistently achieve high levels of performance reliability in newly manufactured engines. Much of the variation in performance reliability is due to the combined effect of tolerances of key engine components, including tip clearances of rotating components and flow areas in turbine nozzles. This research presents system analysis methods for determining the maximum possible tolerances of these key components that will allow a turbine engine to pass a number of specified performance constraints at a selected level of reliability. Through the combined use of a state-of-the-art engine performance code, component clearance loss models, and stochastic simulations, regions of feasible design space can be explored that allow for a pre-determined level of engine reliability. As expected, constraints such as spool speed and fuel consumption that are highly sensitive to certain component tolerances can significantly limit the feasible design space of the component in question. Discussed are methods for determining the bounds of any components feasible design space and for selecting the most economical combinations of component tolerances. Unique to this research is the method that determines the tolerances of engine components as a system while maintaining the geometric constraints of individual components. The methods presented in this work allow for any number of component tolerances to be varied or held fixed while providing solutions that satisfy all performance criteria. The algorithms presented in this research also allow for an individual specification of reliability on any number of performance parameters and geometric constraints. This work also serves as a foundation for an even larger algorithm that can include stochastic simulations and reliability prediction of an engine over its entire life cycle. By incorporating information such as time dependent performance data, known mission profiles, and the influence of maintenance into the component models, it would be possible to predict the reliability of an engine over time. Ultimately, a time-variant simulation such as this could help predict the timing and levels of maintenance that will maximize the life of an engine for a minimum cost.
Assessment of an Innovative Experimental Facility for Testing Diffusing Serpentine Inlets with Large Amounts of Boundary Layer Ingestion
Hylton, Michael Ronnie (Virginia Tech, 2008-07-09)
An innovative experimental facility was developed for testing flush-mounted, diffusing serpentine inlets intended for use on blended-wing-body aircraft. The static ground test facility was able to simulate the boundary layer profile expected to be ingested by inlets mounted on the aft sections of these aircraft. It generated Mach numbers ranging from 0.19 to 0.4 and boundary layer thicknesses between 36% and 45%. The circumferential distortions at the aerodynamic interface plane of the serpentine inlet were also calculated, and ranged between 0.0042 for the lowest Mach number, to 0.0098 for the highest Mach number. Reynolds numbers for the tests ranged between 1.2 million and 2.4 million depending on engine speed and Mach number. The results of the experiment were compared to a previous NASA report, and showed close agreement in distortion patterns and pressure losses at a Mach number of 0.25.
Bedload Transport in Gravel-Bed Streams under a wide range of Shields Stresses
Almedeij, Jaber H. (Virginia Tech, 2002-03-28)
Bedload transport is a complicated phenomenon in gravel-bed streams. Several factors account for this complication, including the different hydrologic regime under which different stream types operate and the wide range of particle sizes of channel bed material. Based on the hydrologic regime, there are two common types of gravel-bed streams: perennial and ephemeral. In terms of channel bed material, a gravel bed may have either unimodal or bimodal sediment. This study examines more closely some aspects of bedload transport in gravel-bed streams and proposes explanations based on fluvial mechanics. First, a comparison between perennial and ephemeral gravel-bed streams is conducted. This comparison demonstrates that under a wide range of Shields stresses, the trends exhibited by the bedload transport data of the two stream types collapse into one continuous curve, thus a unified approach is warranted. Second, an empirical bedload transport relation that accounts for the variation in the make-up of the surface material within a wide range of Shields stresses is developed. The accuracy of the relation is tested using available bedload transport data from streams with unimodal sediment. The relation is also compared against other formulae available in the literature that are commonly used for predicting bedload transport in gravel-bed streams. Third, an approach is proposed for transforming the bimodal sediment into two independent unimodal fractions, one for sand and another for gravel. This transformation makes it possible to carry out two separate computations of bedload transport rate using the bedload relation developed in this study for unimodal sediment. The total bedload transport rate is estimated by adding together the two contributions.
Boundary Layer Control and Wall-Pressure Fluctuations in a Serpentine Inlet
Harper, David Keneda (Virginia Tech, 2000-05-04)
In this thesis, the benefits of boundary layer control (BLC) in improving aerodynamic performance and engine stability were examined in a compact, serpentine inlet exhibiting flow separation. A 1/14-scale turbofan engine simulator provided the flow through the inlet. The inlet's mass flow was measured to be 759 scfm (0.939 lbm/s) with an average throat Mach number of 0.23 when the simulator speed was 40 krpm. Boundary layer suction, blowing, and their combination were used to minimize the inlet's flow separation. The effectiveness of the suction alone and the blowing alone was shown to be approximately equivalent, and the effectiveness of the combined use of both was seen to be better than either one by itself. With blowing and suction flowrates around 1% of the simulator's core flow, the inlet's distortion was lowered by 40.5% (from 1.55% to 0.922%) while the pressure recovery was raised by 9.7% (from 87.2% to 95.6%). With its reduction in distortion, BLC was shown to allow the simulator to steadily operate in a range that would have otherwise been unstable. Minimizing the flow separation within the inlet was shown to directly relate to measurements from flush-mounted microphones along the inlet wall: as the exit distortion decreased the microphone spectrum also decreased in magnitude. The strong relationship between the aerodynamic profiles and the microphone signal suggests that microphones may be used in an active flow control scheme, where the BLC effort can be tailored for different engine operating conditions. Unfortunately, the sensing scheme used in this experiment showed the microphone signal to continue to decrease even when the separation is overly compensated; therefore refinements must be made before it would be practical in a real application.
Boundary Shear Stress Along Vegetated Streambanks
Hopkinson, Leslie (Virginia Tech, 2009-10-20)
This research is intended to determine the role of riparian vegetation in stream morphology. This experiment examined the effects of riparian vegetation on boundary shear stress (BSS) by completing the following objectives: (1) evaluating the effects of streambank vegetation on near-bank velocity and turbulence; (2) determining a method for measuring BSS; and, (3) examining the effects of streambank vegetation on BSS using an existing model. A second order prototype stream, with individual reaches dominated by the three vegetation types (trees, shrubs, and grass) was modeled using a fixed-bed Froude-scale modeling technique. One model streambank of the prototype stream was constructed for each vegetation type in addition to one bank with only grain roughness. Velocity profiles were measured using an acoustic Doppler velocimeter (ADV) and a miniature propeller (MP). A flush-mounted Dantec MiniCTA system was used to measure shear stress at the streambank wall. The addition of vegetation on a sloping streambank increased the streamwise free stream velocity and decreased the near-bank streamwise velocity. The turbulence caused by the upright shrub treatment increased turbulent kinetic energy and Reynolds stresses near the streambank toe, an area susceptible to fluvial erosion. The presence of dense, semi-rigid vegetation may encourage the formation of a wider channel with a vertical streambank. The small range of CTA shear stress measurements (0.02—2.14 Pa) suggested that one estimate can describe a streambank. The law of the wall technique is not appropriate because the velocity profiles did not follow the necessary logarithmic shape. Vegetative roughness present in channels created secondary flow; turbulence characteristics more appropriately estimated BSS. The BSS model predicted velocity fields in similar distribution to that measured by the ADV and MP. BSS calculated using the ray-isovel method for both velocity measurement devices were different than the measured BSS values, likely due to distortions in the measured velocity field. In general, the predicted BSS distribution increased with water depth and decreased with increasing vegetation density. The predicted BSS at the shrub toe indicated a spike in shear stress consistent with TKE estimates.
Breakdown characteristics of nonuniform electric fields in crossflows
Hamby, David William (Virginia Tech, 1993-07-05)
An experimental evaluation of the breakdown characteristics of the nonuniform electric fields established between two spheres and between two points in a crossflow was conducted and the results were then compared to the breakdown characteristics in quiescent air. The aluminum spheres used in this investigation ranged in diameter from 0.635 em to 2.54 em. The points had a radius of curvature of 0.5 mm. The velocities of the crossflow ranged from 23 mls to 58 mls and the gap distances ranged from 0.5 cm to 2.0 cm. Photography was used to determine the effect of the crossflow on the luminous spark for all electrodes. The sparking voltages in the crossflow were a function of the crossflow velocity, electrode size and gap distance. It was concluded that the most significant increase of sparking voltages in a crossflow, as compared to the same configuration in quiescent air, was for the point-point gap at a distance of 2.0 cm for a 58 mls crossflow. As the electrodes were increased in size, the effect of a given crossflow decreased. For the 2.54 cm spheres with a 58 mls crossflow, there was actually a decrease in the sparking voltage as compared to its counterpart in quiescent air. The photographs showed a significant deflection of the spark in the direction of the crossflow for the point-point gap, but no significant deflection was detected for the other electrode geometries.
CFD analysis and redesign of centrifugal impeller flows for rocket pumps
Lupi, Alessandro (Virginia Tech, 1993-12-05)
The analysis and redesign of a centrifugal impeller for a rocket pump is presented in this thesis. A baseline impeller was designed by Rocketdyne for the NASA Marshall Pump Consortium. Initially, the objective was to reduce the circumferential exit flow distortion of the baseline impeller. Later in the study, the objective became raising the head coefficient of the impeller. The study presented in this thesis was also undertaken to demonstrate current CFD capabilities for impeller design. A literature review includes an overview of centrifugal impeller geometries and configurations. Centrifugal impeller performance and secondary flows are discussed, and a summary of studies on the effects of impeller exit and diffuser inlet velocity distortion on diffuser performance is also presented. The flow calculation details and the results of the baseline impeller flow calculations are described. Fourteen redesigned impeller geometries were analyzed using the Moore Elliptic Flow Program, and the results were compared to the baseline geometry in terms of head rise, losses, and exit flow distortions. A final geometry was chosen; this geometry will be built and tested by Rocketdyne. The results show that backward blade lean can be effective in red using the exit flow distortion of the impeller. Tip slots or holes were not beneficial because of the large inlet boundary layer. Also, it appears possible to raise the head coefficient of the baseline impeller without creating excessive flow distortion. The planned testing is necessary to verify the predictions of the flow code.
CFD Modeling of Separation and Transitional Flow in Low Pressure Turbine Blades at Low Reynolds Numbers
Sanders, Darius Demetri (Virginia Tech, 2009-09-28)
There is increasing interest in design methods and performance prediction for turbine engines operating at low Reynolds numbers. In this regime, boundary layer separation may be more likely to occur in the turbine flow passages. For accurate CFD predictions of the flow, correct modeling of laminar-turbulent boundary layer transition is essential to capture the details of the flow. To investigate possible improvements in model fidelity, both two-dimensional and three-dimensional CFD models were created for the flow over several low pressure turbine blade designs. A new three-equation eddy-viscosity type turbulent transitional flow model originally developed by Walters and Leylek was employed for the current RANS CFD calculations. Flows over three low pressure turbine blade airfoils with different aerodynamic characteristics were simulated over a Reynolds number range of 15,000-100,000, and predictions were compared to experiments. The turbulent transitional flow model sensitivity to inlet turbulent flow parameters showed a dependence on free-stream turbulence intensity and turbulent length scale. Using the total pressure loss coefficient as a measurement of aerodynamic performance, the Walters and Leylek transitional flow model produced adequate prediction of the Reynolds number performance in the Lightly Loaded blade. Furthermore, the correct qualitative flow response to separated shear layers was observed for the Highly Loaded blade. The vortex shedding produced by the separated flow was largely two-dimensional with small spanwise variations in the separation region. The blade loading and separation location was sufficiently predicted for the Aft-Loaded L1A blade flowfield. Investigations of the unsteady flowfield of the Aft-Loaded L1A blade showed the shear layer produced a large separation region on the suction surface. This separation region was located more downstream and significantly reduced in size when impinged upon by the upstream wakes, thus improving the aerodynamic performance consistent with experiments. For all cases investigated, the Walters and Leylek transitional flow model was judged to be sufficient for understanding the separation and transition characteristics, and superior to other widely-used turbulence models in accuracy of describing the details of the transitional and separated flow. This research characterized and assessed a new model for low Reynolds number turbine aerodynamic flow prediction and design improvement.
Computational Fluid Dynamics Simulations of Hydraulic Energy Absorber
Chiu, Ya-Tien (Virginia Tech, 1999-07-21)
Hydraulic energy absorbers may be described as high-loss centrifugal turbomachines arranged to operate as stalled torque converters. The device absorbs the kinetic energy of a vehicle in motion and dissipates the energy into water. A steady, single-phase, Computational Fluid Dynamics (CFD) simulation has been performed to investigate the flow field in a hydraulic energy absorber. It was determined that to better predict the performance of the energy absorber, more sophisticated modeling approaches may be needed. In this research, a steady, two-phase calculation with basic turbulence modeling was used as a first assessment. The two-phase model was used to investigate cavitation effects. Unsteady and advanced turbulence modeling techniques were then incorporated into single-phase calculations. The Multiple Reference Frame (MRF) Technique was used to model the interaction between the rotor and the stator. The calculations provided clearer details of the flow field without dramatically increasing the computational cost. It was found that unsteady modeling was necessary to correctly capture the close coupling between the rotor and the stator. The predicted torque in the unsteady calculations was 70% of the experimental value and twice of the result in the steady-state calculations. It was found that the inaccuracy of torque prediction was due to (1) high pressures in the regions with complicated geometrical boundaries and, (2) dynamic interactions between the rotor and the stator were not captured fully. It was also determined that the unrealistically low pressure values were not caused by the physical cavitation, but by the lack of proper boundary conditions for the model. Further integration of the modeling techniques studied would improve the CFD results for use in the design of the energy absorber.
A Computational Framework for Fluid-Thermal Coupling of Particle Deposits
Paul, Steven Timothy (Virginia Tech, 2018-06-13)
This thesis presents a computational framework that models the coupled behavior between sand deposits and their surrounding fluid. Particle deposits that form in gas turbine engines and industrial burners, can change flow dynamics and heat transfer, leading to performance degradation and impacting durability. The proposed coupled framework allows insight into the coupled behavior of sand deposits at high temperatures with the flow, which has not been available previously. The coupling is done by using a CFD-DEM framework in which a physics based collision model is used to predict the post-collision state-of-the-sand-particle. The collision model is sensitive to temperature dependent material properties of sand. Particle deposition is determined by the particle's softening temperature and the calculated coefficient of restitution of the collision. The multiphase treatment facilitates conduction through the porous deposit and the coupling between the deposit and the fluid field. The coupled framework was first used to model the behavior of softened sand particles in a laminar impinging jet flow field. The temperature of the jet and the impact surface were varied(T^* = 1000 – 1600 K), to observe particle behavior under different temperature conditions. The Reynolds number(Rejet = 20, 75, 100) and particle Stokes numbers (Stp = 0.53, 0.85, 2.66, 3.19) were also varied to observe any effects the particles' responsiveness had on deposition and the flow field. The coupled framework was found to increase or decrease capture efficiency, when compared to an uncoupled simulation, by as much as 10% depending on the temperature field. Deposits that formed on the impact surface, using the coupled framework, altered the velocity field by as much as 130% but had a limited effect on the temperature field. Simulations were also done that looked at the formation of an equilibrium deposit when a cold jet impinged on a relatively hotter surface, under continuous particle injection. An equilibrium deposit was found to form as deposited particles created a heat barrier on the high temperature surface, limiting more particle deposition. However, due to the transient nature of the system, the deposit temperature increased once deposition was halted. Further particle injection was not performed, but it can be predicted that the formed deposit would begin to grow again. Additionally, a Large-Eddy Simulation (LES) simulation, with the inclusion of the Smagorinsky subgrid model, was performed to observe particle deposition in a turbulent flow field. Deposition of sand particles was observed as a turbulent jet (Re jet=23000,T_jet^*= 1200 K) impinged on a hotter surface(T_surf^*= 1600 K). Differences between the simulated flow field and relevant experiments were attributed to differing jet exit conditions and impact surface thermal conditions. The deposit was not substantive enough to have a significant effect on the flow field. With no difference in the flow field, no difference was found in the capture efficiency between the coupled and decoupled frameworks.
A Computational Study of Compressor Inlet Boundary Conditions with Total Temperature Distortions
Eisemann, Kevin Michael (Virginia Tech, 2005-06-16)
A three-dimensional CFD program was used to predict the flow field that would enter a downstream fan or compressor rotor under the influence of an upstream thermal distortion. Two distortion generation techniques were implemented in the model; (1) a thermal source and (2) a heated flow injection method. Results from the investigation indicate that both total pressure and velocity boundary conditions at the compressor face are made non-uniform by the upstream thermal distortion, while static pressure remains nearly constant. Total pressure at the compressor face was found to vary on the order of 10%, while velocity varies from 50-65%. Therefore, in modeling such flows, neither of these latter two boundary conditions can be assumed constant under these conditions. The computational model results for the two distortion generation techniques were compared to one another and evaluations of the physical practicality of the thermal distortion generation methods are presented. Both thermal distortion methods create total temperature distortion magnitudes at the compressor face that may affect rotor blade vibration. Both analyses show that holding static pressure constant is an appropriate boundary condition for flow modeling at the compressor inlet. The analyses indicate that in addition to the introduction of a thermal distortion, there is a potential to generate distortion in total pressure, Mach number, and velocity. Depending on the method of thermally distorting the inlet flow, the flow entering the compressor face may be significantly non-uniform. The compressor face boundary condition results are compared to the assumptions of a previous analysis (Kenyon et al., 2004) in which a 25 R total temperature distortion was applied to a computational fluid dynamics (CFD) model of a fan geometry to obtain unsteady blade pressure loading. Results from the present CFD analyses predict similar total temperature distortion magnitudes corresponding to the total temperature variation used in the Kenyon analyses. However, the results indicate that the total pressure and circumferential velocity boundary conditions assumed uniform in the Kenyon analyses could vary by the order of 2% in total pressure and approximately 8% in velocity distortion. This supports the previously stated finding that assuming a uniform total pressure profile at the compressor inlet may be an appropriate approximation with the presence of a weak thermal distortion, while assuming a constant circumferential velocity boundary condition is likely not sufficiently accurate for any thermal distortion. In this work, the referenced Kenyon investigation and others related to the investigation of distortion-induced aeromechanical effects in this compressor rotor have assumed no aerodynamic coupling between the duct flow and the rotor. A full computational model incorporating the interaction between the duct flow and the fan rotor would serve to alleviate the need for assuming boundary conditions at the compressor inlet.
Computational study of hub corner stall in an axial compressor rotor
Gailliot, John A. (Virginia Tech, 1995-08-15)
The Deverson rotor, a single stage axial compressor designed to simulate a multistage axial compressor, was studied computationally using a 3-D Navier-Stokes solver, the Moore Elliptic Flow Program. A one equation, q-L, transitional turbulence model was used with MEFP for closure of the transport equations. The calculation was used to study the physics and flow mechanisms affecting hub corner stall. Preprocessing and post processing programs were written to aid this study, a grid generation program and a streakline visualization program, respectively. First, computational 2-D cascade studies were performed to study the effects of free stream turbulence level and incidence angle on suction surface boundary layer development. The results showed the correct trends in boundary layer transition and separation, loss production, and deviation angles. Velocity measurements taken at the exit of the Deverson rotor were made available by Rolls-Royce for comparison with the 3-D calculation results. The q-L turbulence model predicted the existence of the hub comer stall, but under predicted the size of the corner stall. It failed to predict the radial migration of the associated loss core. However, the calculation did reveal details of the flow that affect comer stall. These included boundary layer transition and separation on the suction surface, hub and suction surface secondary flows, and radial relief. Streaklines were useful in visualizing and understanding these flow details. A preliminary 3-D calculation was performed with a two-equation, q-w, turbulence model. This turbulence model more accurately predicted the comer stall including radial migration of the loss core.
A computational study of the 3D flow and performance of a vaned radial diffuser
Akseraylian, Dikran (Virginia Tech, 1996-08-14)
A computational study was performed on a vaned radial diffuser using the MEFP (The Moore Elliptic Flow Program) flow code. The vaned diffuser studied by Dalbert et al. was chosen as a test case for this thesis. The geometry and inlet conditions were established from this study. The performance of the computational diffuser was compared to the test case diffuser. The CFD analysis was able to demonstrate the 3D flow within the diffuser. An inlet conditions analysis was performed to establish the boundary conditions at the diffuser inlet. The given inlet flow angles were reduced in order to match the specified mass flow rate. The inlet static pressure was held constant over the height of the diffuser. The diffuser was broken down into its subcomponents to study the effects of each component on the overall performance of the diffuser. The diffuser inlet region, which comprises the vaneless and semi-vaneless spaces, contains the greatest losses, 56%, but the highest static pressure rise, 54%. The performance at the throat was also evaluated and the blockage and pressure recovery were calculated. The results show the static pressure comparison for the computational study and the test case. The overall pressure rise of the computational study was in good agreement with the measured pressure rise. The static pressure and total pressure loss distributions in the inlet region, at the throat, and in the exit region of the diffuser were also analyzed. The flow development was presented for the entire diffuser. The 3D flow calculations were able to illustrate a leading edge recirculation at the hub, caused by an inlet skew and high losses at the hub, and the secondary flows in the diffuser convected the high losses. The study presented in this thesis demonstrated the flow development in a vaned diffuser and its subcomponents. The performance was evaluated by calculating the static pressure rise, total pressure losses, and throat blockage. It also demonstrated current CFD capabilities for diffusers using steady 3D flow analysis.
Computer Aided Analysis of Smoke Stack Designs
Servaites, Joseph Charles (Virginia Tech, 1996-09-01)
The purpose of this research is to analyze the statics and dynamics of steel smoke stacks subject to excitation by aerodynamic forces. The wind loads experienced by smoke stacks arise from various phenomenon, the most prominent of which are static drag load, vortex shedding, and atmospheric turbulence. The nature of these loading sources around a cylinder are studied in detail. Both static and dynamic loads are capable of producing large tip deflections, and are of the most prominent design criteria for stack designers. A computer program, STACK1, has been created by modifying an existing analysis code, BEAM8, to be used specifically for stack analysis. This analysis code utilizes the transfer matrix method to perform detailed bending and vibration analyses. This new software has been developed to check stack designs for compliance with appropriate steel stack standards, and provide the designer with information regarding the static and dynamic response of the structure. A detailed analysis is performed to demonstrate the validity of approximating a tapered Timoshenko beam with a series of continuous, constant cross-section beams.
The Design and Construction of a 20" x 20" Mach 2.0 Blowdown Wind Tunnel to Characterize the Lift and Drag of Irregularly Shaped Fragments
Larson, Christopher Whitford (Virginia Tech, 2011-04-25)
A supersonic wind tunnel, with a 20" x 20'" test section cross sectional area, was designed and constructed at the Techsburg Wind Tunnel Facility in order to determine the lift and drag on irregularly shaped fragments in supersonic flow. Prior to beginning the wind tunnel design process, a blowdown analysis model was created in order to determine the influence of a number of parameters on tunnel run time and test gas properties throughout the tunnel circuit. The design of the settling chamber, test section, supersonic nozzles, diffuser, and exhaust are presented in this thesis. Diffuser performance has a large influence on wind tunnel efficiency and run time. Therefore, significant efforts should be taken in order to attain the highest possible pressure recovery within the diffuser. The design of wind tunnel components, as well as their stress analysis, was conducted using SolidWorks. The control valve and silencer were sized and selected for the expected tunnel operating conditions. Since the control valve tends to encompass a significant portion of the overall tunnel cost, care must be taken to ensure it has a large enough flow capacity to produce the desired test conditions. Also, attempts must be made to accurately predict the total pressure loss through the silencer, since this loss can have a large impact on the total pressure ratio necessary to produce the design Mach number. Upon completion of the design process, the supersonic wind tunnel was assembled, and shakedown testing was conducted. During shakedown testing it was determined that the wind tunnel was capable of producing Mach 2 flow in the test section. Following shakedown testing, a flow survey was conducted in order to ensure uniform Mach number flow exists throughout the region occupied by the fragments. Based on the flow survey it was determined that within the middle 60% of the test section, the average Mach number was 1.950 and varied by only 0.56% within this region. Two irregularly shaped fragments were tested at Mach 2 flow, over an effective 360° pitch sweep, with wind tunnel runs performed every 10 degrees. Based on the measured force data for both fragments, the lift appeared to follow a sinusoidal curve, with minimum values at 0, 90, and 180° balance pitch angle, and maximum values occurring around 45 and 135° pitch angle. The drag force was observed to follow a gradual curve with minimum values at 0 and 180° balance pitch angle, as expected since the fragment presented area is generally least in this orientation. The maximum drag was found to occur at a balance pitch angle of 90°, once again as expected since the fragment presented area is generally greatest at this angle. It was also observed that the fragment drag tended to be greater for a fragment orientation which places the concave side of the fragment into the direction of the flow.
The Design and Evaluation of a High Frequency Fore-Aft Probe
Meier, David Alan (Virginia Tech, 1997-12-11)
A high-frequency surge and stall sensing fore-aft probe was developed at the Turbomachinery Research Laboratory at Virginia Tech. The probe was designed to detect surge and stall based on changes in large regions of flow behind a turbofan engine compressor fan. The probe exhibited excellent frequency response capabilities and can accurately measure data with response well above anticipated surge frequencies. A CFD analysis was performed in order to gain more understanding about the flow around the probe. The results of the CFD analysis and the experimental testing were analyzed and presented. The probe worked as expected when the flow was aligned with the upstream pressure transducer. Thus, it can be used to determine the onset of surge and stall. However, the probe was found to be extremely sensitive to off-axis flows. Design improvements are suggested in order to increase its capabilities.
Design of a Total Pressure Distortion Generator for Aircraft Engine Testing
Cramer, Kevin Brendan (Virginia Tech, 2002-04-29)
A new method and mechanism for generating non-uniform, or distorted, aircraft engine inlet flow is being developed in order to account for dynamic changes during the creation and propagation of the distortion. Total pressure distortions occur in gas turbine engines when the incoming flow is disturbed. Dynamic total pressure changes may happen slowly, or may occur very rapidly. The disturbance of the incoming flow can change engine operating characteristics, including lowering the surge limit and creating High Cycle Fatigue incidents. In order to create a distorted flow with dynamic characteristics, a mechanism must be developed that when actuated, can change the distortion pattern and intensity with respect to time. This work covers the initial design of both the distorting and actuating device. The design chosen is a low force design that is practically independent of flow forces. This allows the system to be easily sized for all flow conditions. The study also includes developing the working design into an overall prototype. Testing is also performed to validate the design as the most advantageous choice.

Browsing by Author "Dancey, Clinton L."

Results Per Page

Sort Options