Multidisciplinary assessment of a year 2035 turbofan propulsion system

A conceptual design of a year 2035 turbofan is developed and integrated onto a year 2035 aircraft model. The mission performance is evaluated for CO2, noise and NOx and is compared with a notional XWB/A350-model. An OGV heat exchanger is then studied rejecting heat from an electric generator, and its top-level performance is evaluated. The fan, the booster and the low-pressure turbine of the propulsion system are subject to more detailed aero design based on using commercial design tools and CFD-optimization. Booster aerodynamic modelling output is introduced back into the performance model to study the integrated performance of the component. The top-level performance aircraft improvements are compared to top-level-trends and ICAO estimates of technology progress potential, attempting to evaluate whether there is some additional margin for efficiency improvement beyond the ICAO technology predictions for the same time frame

Design of compressor blades considering efficiency and stability using CFD based optimization

To design a highly loaded axial transonic compressor several objectives need to be considered simultaneously. From an aerodynamic perspective, one of the major requirements is high efficiency at a specific operating condition where the fuel consumption is of main interest. Furthermore, the compressor needs to have a sufficient stall-margin along the entire flight envelope to ensure a stable operating range. This work is focused on creating an efficient design method which produces a trade-off between high stall margin and high efficiency. The design method is based on an automatic multiobjective optimization process divided into two steps. In the first step, 2D blade profiles are optimized where both efficiency and stall margin are considered. Once the optimization is finished the selected profiles are stacked together to be further optimized in 3D. When going to the second step, i.e. a 3D optimization, one can focus on a smaller set of design variables thereby reducing the time to get what is considered the optimal solution. The results show that it is possible to rate designs with potential of having high stall margin and high efficiency both in the 2D and 3D optimization. The main contribution in this work is the design method, which offers an efficient way of designing robust blades where the designer can decide the best trade off between stall margin at part speed and efficiency at the design point. Copyright \ua9 2012 by ASME

Validation of a Forced Response Prediction Method for Design of Axial Compressors

The linearized time-harmonic Navier-Stokes solver LINNEA is used to evaluate the forcing of a rotor blade in the transonic compressor Hulda, at part speed. Hulda is a 1\ubd stage demonstrator compressor consisting of a variable inlet guide vanes (VIGV), rotors, stators and outlet guide vanes (OGV). The forcing of the rotor is evaluated for different setting angles of the VIGV. The mesh study shows that, for this computational setup, a mesh independent solution was obtained in RANS simulation using CFX and in the linearized Navier-Stokes solver LINNEA for the same grid resolution.The results obtained using LINNEA are compared to results from three URANS simulations using CFX. The first URANS case uses scaled geometries and rotational periodic boundary conditions. The second and third case use the true geometry in conjunction with rotational periodic boundary conditions: “profile transformation” and with time-lagged periodic boundary conditions: “time transformation” in CFX’ nomenclature, which corresponds to time-inclined computational planes. LINNEA is run with two different boundary conditions at the inlet to the rotor domain, obtained from a RANS and URANS simulation, respectively.The forcing is evaluated at engine orders 15, 30 and 45, corresponding to VIGV passing frequency and multiples thereof. The results show that the amplitude of the tangential force variation calculated with the different methods and boundary conditions, is within a 1.3% interval based on the total tangential force for the nominal (0 degree) VIGV setting and within a 3.3% interval for the VIGV setting angle of 30 degrees at engine order 15.Using a linear time-harmonic Navier-Stokes solver to calculate forcing of a rotor blade interacting an upstream component is shown to be a possible and attractive alternative to URANS calculations. A linear harmonic simulation is less computationally demanding than a URANS simulation. The mean flow solution required by the linearized solver does not incur any additional computational effort since it is usually already available from general performance calculations. Further is shown that for URANS analyses a scaling of the model can be neglected since results obtained for a scaled model are in good agreement with results obtained for an unscaled model using profile transformation (PT) to handle the variation of pitch between components

CFD optimization of a transonic compressor using multiobjective GA and metamodels

This paper present an automatic design process where a non-deterministic, global search optimization is utilized to optimize a first stage rotor of a highly loaded transonic compressor. The first part is focused on finding the best suited metamodel that can be used to accelerate the design process. The second part presents the results of using the meta model within the design process for an industry relevant case. Using the radial basis functions as acceleration technique for the optimization was seen to be very successful. The meta model assisted optimization reduced the total design time from approximately 2 weeks to 3.5 days given that 8 designs could run in parallel on a cluster. The 3D optimization produced a pareto front where it was possible to select blades having either high efficiency or high stability

Balancing efficiency and stability in the design of transonic compressor stages

The paper describes an efficient design method for highly loaded transonic compressor stages which considers a balance between efficiency at the design point and stability at part-speed. Because of the high dimensionality of the problem, two levels of model complexity are included in the design method. The first level consists of optimizing the rotor and stator profiles positioned at three stream tubes along the span. The stream tube height and radius variations are included in the computational domain and it is analyzed using a 3D RANS solver incorporating a mixing plane between the components. Due to the relatively low complexity of this quasi-3D analysis, it is fast enough to explore a large design space. With the aid of the resulting pareto-fronts, the designer can select profiles with the appropriate trade between stability and efficiency. The initial 3D compressor stage is generated based on the selected 2D profiles and the method continues to the higher complexity mode where the 3D shapes of the rotor and stator are optimized to gain further performance improvements. To verify that the design method is feasible, it is used to re-design the first compressor stage of a three-stage highly loaded transonic compressor. The compressor stage designed with the presented design method has higher part-speed stability without a compromise in the efficiency compared to the original design. This is also verified when analyzing the new design in the full compressor module

The Impact Of Manufacturing Variations On Performance Of A Transonic Axial Compressor Rotor

In this paper, the impact of manufacturing variations on performance of an axial compressor rotor are evaluated at design rotational speed. The geometric variations from the design intent were obtained from an optical coordinate measuring machine and used to evaluate the impact of manufacturing variations on performance and the flow field in the rotor. The complete blisk is simulated using 3D CFD calculations, allowing for a detailed analysis of the impact of geometric variations on the flow. It is shown that the mean shift of the geometry from the design intent is responsible for the majority of the change in performance in terms of mass flow and total pressure ratio for this specific blisk. In terms of polytropic efficiency, the measured geometric scatter is shown to have a higher influence than the geometric mean deviation. The geometric scatter around the mean is shown to impact the pressure distribution along the leading edge and the shock position. Furthermore, a blisk is analyzed with one blade deviating substantially from the design intent, denoted as blade 0. It is shown that the impact of blade 0 on the flow is largely limited to the blade passages that it is directly a part of. The results presented in this paper also show that the impact of this blade on the flow field can be represented by a simulation including 3 blade passages. In terms of loss, using 5 blade passages is shown to give a close estimate for the relative change in loss for blade 0 and neighboring blades

CFD Optimization of a Transonic Compressor Stage with a Large Tip Gap

Large tip gaps can be found in the rear stages of transonic compressors. If the size of the tip gap is large in relation to the blade height it will likely affect the flow in the rotor passage significantly. Therefore, including a large tip gap in the optimization process of a compressor stage can already be of importance in the early design phase.In the present study, a transonic compressor stage is optimized with and without a large tip gap (2.5% of the rotor leading edge span) with respect to part speed stability and polytropic efficiency at a design point. The performance is evaluated using 3D CFD calculations. The two approaches are compared to determine the importance of including the tip gap in the optimization.It is shown that, when the compressor stage is optimized with a tip gap, redistribution of mass flow in the rotor passage affects the design at mid span and near the hub. A lower stagger angle is preferred away from the tip region to allow for a higher mass flow at lower spanwise positions.The k-epsilon turbulence model with wall functions is used to evaluate the performance of the stages during optimization. To support the use of wall functions, Chien’s low-Reynolds model with a more dense mesh is used to evaluate the polytropic efficiency of a number of stages with a tip gap. The results show that the ranking of designs using a low-Reynolds model show the same trend as using wall functions

Validation of a Forced Response Prediction Method for Design of Axial Compressors

The linearized time-harmonic Navier-Stokes solver LINNEA is used to evaluate the forcing of a rotor blade in the transonic compressor Hulda, at part speed. Hulda is a 1\ubd stage demonstrator compressor consisting of a variable inlet guide vanes (VIGV), rotors, stators and outlet guide vanes (OGV). The forcing of the rotor is evaluated for different setting angles of the VIGV. The mesh study shows that, for this computational setup, a mesh independent solution was obtained in RANS simulation using CFX and in the linearized Navier-Stokes solver LINNEA for the same grid resolution.The results obtained using LINNEA are compared to results from three URANS simulations using CFX. The first URANS case uses scaled geometries and rotational periodic boundary conditions. The second and third case use the true geometry in conjunction with rotational periodic boundary conditions: “profile transformation” and with time-lagged periodic boundary conditions: “time transformation” in CFX’ nomenclature, which corresponds to time-inclined computational planes. LINNEA is run with two different boundary conditions at the inlet to the rotor domain, obtained from a RANS and URANS simulation, respectively.The forcing is evaluated at engine orders 15, 30 and 45, corresponding to VIGV passing frequency and multiples thereof. The results show that the amplitude of the tangential force variation calculated with the different methods and boundary conditions, is within a 1.3% interval based on the total tangential force for the nominal (0 degree) VIGV setting and within a 3.3% interval for the VIGV setting angle of 30 degrees at engine order 15.Using a linear time-harmonic Navier-Stokes solver to calculate forcing of a rotor blade interacting an upstream component is shown to be a possible and attractive alternative to URANS calculations. A linear harmonic simulation is less computationally demanding than a URANS simulation. The mean flow solution required by the linearized solver does not incur any additional computational effort since it is usually already available from general performance calculations. Further is shown that for URANS analyses a scaling of the model can be neglected since results obtained for a scaled model are in good agreement with results obtained for an unscaled model using profile transformation (PT) to handle the variation of pitch between components

CFD Optimization of a Transonic Compressor Stage with a Large Tip Gap

Large tip gaps can be found in the rear stages of transonic compressors. If the size of the tip gap is large in relation to the blade height it will likely affect the flow in the rotor passage significantly. Therefore, including a large tip gap in the optimization process of a compressor stage can already be of importance in the early design phase.In the present study, a transonic compressor stage is optimized with and without a large tip gap (2.5% of the rotor leading edge span) with respect to part speed stability and polytropic efficiency at a design point. The performance is evaluated using 3D CFD calculations. The two approaches are compared to determine the importance of including the tip gap in the optimization.It is shown that, when the compressor stage is optimized with a tip gap, redistribution of mass flow in the rotor passage affects the design at mid span and near the hub. A lower stagger angle is preferred away from the tip region to allow for a higher mass flow at lower spanwise positions.The k-epsilon turbulence model with wall functions is used to evaluate the performance of the stages during optimization. To support the use of wall functions, Chien’s low-Reynolds model with a more dense mesh is used to evaluate the polytropic efficiency of a number of stages with a tip gap. The results show that the ranking of designs using a low-Reynolds model show the same trend as using wall functions