Razvan Virgil Florea

Preliminary Design for Embedded Engine Systems

This paper presents a collaborative research program to advance the analysis and design capabilities for embedded engines in Blended Wing Body Boundary Layer Ingesting (BWB- BLI aircraft. Embedded engine propulsion systems for hybrid wing/body aircraft face several key technical issues stemming from the ingestion of the low-momentum boundary layer to the close coupling of the airframe and propulsion systems in ways that challenge current design procedures and require a system design perspective. To address these challenges, a new high performance flow-control-enabled embedded engine inlet was designed. The inlet bleed flow control actuation was integrated with the aircraft Environmental Control System (ECS), thus providing a viable robust inlet design with improved system performance while supplying the flow required by the ECS. Without flow control, a thick ingested boundary layer leads to high levels of distortion at the AIP plane and impacts the overall fan performance and operability. The impact of inlet distortion on fan performance was estimated through numerical simulations based on unsteady flow simulations. Of particular interest, is the increased flow unsteadiness in the fan passages and its associated detrimental impact on blade aeromechanics and acoustic responses. The proposed flow control solution is predicted to have significant reduction in the harmonic content associated with blade strain. In addition, reductions in total radiated acoustic power are predicted to be achievable, especially at well cut-on modes, significantly reducing aircraft noise at approach conditions. These results suggest that inlet flow control technology has the potential to address the challenges of BWB-BLI aircraft.

Aeromechanics Analysis of a Boundary Layer Ingesting Fan

Abstract Boundary layer ingesting propulsion systems have the potential to significantly reduce fuel burn but these systems must overcome the challenges related to aeromechanics—fan flutter stability and forced response dynamic stresses. High-fidelity computational analysis of the fan aeromechanics is integral to the ongoing effort to design a boundary layer ingesting inlet and fan for fabrication and wind-tunnel test. A three-dimensional, time-accurate, Reynolds-averaged Navier Stokes computational fluid dynamics code is used to study aerothermodynamic and aeromechanical behavior of the fan in response to both clean and distorted inflows. The computational aeromechanics analyses performed in this study show an intermediate design iteration of the fan to be flutter-free at the design conditions analyzed with both clean and distorted in-flows. Dynamic stresses from forced response have been calculated for the design rotational speed. Additional work is ongoing to expand the analyses to off-design conditions, and for on-resonance conditions.

Optimization of Bleed-Flow-Control for an Aggressive Serpentine Duct

A procedure for designing flow-control-enabled aggressive serpentine duct shapes as part of an Integrated Total Aircraft Power Systems (ITAPS TM ) study is presented. Some military aircraft are driven towards serpentine shaped inlet designs to increase survivability through reduction in engine visibility. Maintaining the engine inflow quality with low total pressure losses and low engine face total pressure distortions generally requires a relatively long duct. Long ducts, significantly increase the size and the weight of the overall air vehicle system result in limitations to the vehicle’s overall performance. Without boundary layer control, a shorter (more aggressive) inlet is not a viable solution due to massive flow separation resulting in high total pressure losses and inlet distortion along with overall low system performance. Flow control has the potential to eliminate flow separation in these aggressive ducts and was included in the present study as an enabling technology. However, for the overall system performance, flow control by itself may not be a viable solution due to penalties associated high actuation requirements, power, weight and flow source or sink. In addition, the robustness of the flow control in an aggressive serpentine duct must be considered since it has to be maintained for all possible mission conditions. The present methodology consists of a novel approach of integrating a simple inlet bleed-flow control actuation with the aircraft Environmental Control System (ECS), thus providing a viable robust inlet design with impr oved system performance while supplying the flow required by the ECS. A new inlet optimization tool, OPDUCT, was created and used to design a flow-control-enabled aggressive serpentine duct and evaluate its performance. It employs a hierarchy of high and low fidelity models that allow for optimizing duct geometry to yield high inlet total pressure recovery and low distortion. The resulting inlet total pressure recovery and distortion were then assessed to capture the impact on engine operability and aircraft performance.

Aerodynamic Analysis of a Boundary-Layer-Ingesting Distortion-Tolerant Fan

The paper describes the aerodynamic CFD analysis that was conducted to address the integration of an embedded-engine (EE) inlet with the fan stage. A highly airframe-integrated, distortion-tolerant propulsion preliminary design study was carried out to quantify fuel burn benefits associated with boundary layer ingestion (BLI) for “N+2” blended wing body (BWB) concepts. The study indicated that low-loss inlets and high-performance, distortion-tolerant turbomachines are key technologies required to achieve a 3–5% BLI fuel burn benefit relative to a baseline high-performance, pylon-mounted, propulsion system. A hierarchical, multi-objective, computational fluid dynamics-based aerodynamic design optimization that combined global and local shaping was carried out to design a high-performance embedded-engine inlet and an associated fan stage. The scaled-down design will be manufactured and tested in NASA’s 8′×6′ Transonic Wind Tunnel. Unsteady calculations were performed for the coupled inlet and fan rotor and inlet, fan rotor and exit guide vanes. The calculations show that the BLI distortion propagates through the fan largely un-attenuated. The impact of distortion on the unsteady blade loading, fan rotor and fan stage efficiency and pressure ratio is analyzed. The fan stage pressure ratio is provided as a time-averaged and full-wheel circumferential-averaged value. Computational analyses were performed to validate the system study and design-phase predictions in terms of fan stage performance and operability. For example, fan stage efficiency losses are less than 0.5–1.5% when compared to a fan stage in clean flow. In addition, these calculations will be used to provide pretest predictions and guidance for risk mitigation for the wind tunnel test.Copyright

RANS Simulations for Sensitivity Analysis of Compressor Transition Duct

This paper presents a numerical investigation of a strutted annular transition duct used to connect the low pressure and high pressure compressors of aircraft gas turbine engine. Data was generated for oneand six-strut configurations with the United Technologies (UTC) flow solver. For reference, some cases were also run with the ANSYS FLUENT software package. The validity of the computed velocity and pressure loading distributions was established with the existing experimental data available in the open literature. Mean streamwise velocity profiles are in good agreement with data along the entire length of the duct with some discrepancies in the boundary layers adjacent to each casing. Axial velocity distributions at all locations show a good match in the width of the wake. However, the wake strength is not always well matched. Axial velocity contours illustrate a well-defined wake at the strut trailing edge with no significant regions of flow separations, similar to the experimental data set. Obtained axial static pressure loading distributions along the midline of the duct, about the strut and duct-strut combination indicate good match with measurements. The static pressure loading distributions along the strut at different heights are presented and compare very well with experiment. Additionally, at 10 percent strut height the superposition of strut and duct static pressure distributions shows good agreement between simulation and theoretical data up to 70 percent length. The loss distributions across the duct at four axial locations and integrated losses indicate increasing development of loss near the endwalls through the duct. Finally, sensitivity studies examining the influence of duct length and Mach number on pressure loading were also performed for the case of the one-strut duct.