Bambang I. Soemarwoto

X-LES Simulations Using a High-Order Finite-Volume Scheme

This paper focuses on numerical aspects for hybrid RANS–LES computations using the X-LES method. In particular, the impact of using a high-order finite-volume scheme is considered. The finite-volume scheme is fourth-order accurate on non-uniform, curvilinear grids, has low numerical dispersion and dissipation, and is based on the skew-symmetric form of the compressible convection operator, which ensures that kinetic energy is conserved by convection. A limited grid convergence study is performed for the flow over a rounded bump in a square duct. The fourth-order results are shown to depend only mildly on the grid resolution. In contrast, second-order results require at least half the mesh size to become comparable to the fourth-order results. Additionally, the high-order method is extended with shock-capturing capability in such a way that interference with the subgrid-scale model is avoided. The suitability of this extension is demonstrated by means of a supersonic flow over a cavity.

Performance evaluation of gas turbine labyrinth seals using computational fluid dynamics

The paper presents an investigation on the characteristics of flow through labyrinth seals. The focus of the paper lies in the application of the Computational Fluid Dynamics (CFD) methodology. The Reynolds-Averaged Navier-Stokes equations are employed as the flow governing equations. Turbulence is incorporated through a variant of the two-equation k-ω turbulence model. Three test cases are considered. The first test case concerns a labyrinth seal configuration with a honeycomb land. The computational results are compared to those obtained from seal test rig measurements. The second test case addresses the same labyrinth seal where the honeycomb land is replaced by a solid smooth land. The third test case addresses the flow through a labyrinth seal with canted knives. The CFD method is considered as an analysis tool complementary to rig-testing and enables investigating the effect of new seal design features. Additionally CFD is seen as a tool to support the correct representation of test-data in semiempirical engineering models for seal design. An industrial perspective is presented towards the exploitation of these modeling capabilities for real-life design of seals.Copyright

Advanced Seal Test Rig Validation and Operation

Advanced seals have been identified as critical in meeting engine goals for specific fuel consumption, thrust-to-weight ratio, emissions, durability, and operating costs. In a direct effort to reduce the parasitic leakage, a high-temperature, high-speed seal test rig with Active Clearance Control (ACC) has been designed, built and validated by the National Aerospace Laboratory (NLR) in the Netherlands within a collaborative program with Sulzer Metco Turbine Components (SMTC) and Pratt & Whitney (P&W). NLR’s new seal test rig is capable to evaluate seals for the next generation gas turbine engines. It will test air seals (i.e., labyrinth, brush, and new seal concepts) in near gas turbine engine environment conditions of high temperature to 815 °C (1500 °F), high pressure to 2400 kPa (335 psid), high surface speeds to 365 m/s (1200 ft/s). Seal flows for typical engine seal clearances between 0.12 mm (0.005 inch) and 0.65 mm (0.025 inch) can be measured without changing test articles but by using the ACC system. A compressed air facility at the German-Dutch Windtunnel, located at the NLR site, delivers the required compressed clean and dry air. This paper describes the design, the instrumentation, the control system and the validation of the test rig. The rig certification was achieved by validating test measurements using a known three knife-edges stepped labyrinth seal. This paper also addresses the NLR’s CFD and engineering tool development to predict the seal performance.© 2006 ASME

Analysis of store separation from a generic twin-engine turboprop aircraft

This paper describes a CFD methodology and its application to the analysis of torpedo separation and trajectory, released from a generic twin-engine turboprop aircraft. To address such a realistic aircraft configuration, the methodology employs key technologies in the area of structured grid generation and deformation. The propeller effects are assessed on the basis of power-off and power-on steady simulations of the aircraft with the torpedo in captive condition. The full-scale effects, due to differences in Mach number and Reynolds number, are assessed on the basis of full-scale and model-scale computations involving steady and unsteady flow simulation with the torpedo freely falling away from the aircraft under the gravity force. The differences due the full-scale effects in the translation and rotation of the torpedo are presented.

Aerodynamic design of gas turbine engine intake duct

Purpose The purpose of this paper is to provide a design solution of an engine intake duct suitable for delivering air to the compressor of a gas turbine engine of a general aviation turboprop aircraft, where the initial duct shape suffers a problem of flow distortion due to flow separation at the compressor inlet. Design/methodology/approach Aerodynamic design uses a three-dimensional inverse-by-optimization approach where the deviation from a desirable target pressure distribution is minimized by means of the adjoint method. Findings By virtue of a minimization algorithm, the specified target pressure distribution does not necessarily have to be fully realizable to drive the initial pressure distribution towards one with a favourable pressure gradient. The resulting optimized engine intake duct features a deceleration region, in a diverging channel, followed by an acceleration region, in a contracting channel, inhibiting flow separation on the compressor inlet plane. Practical implications The flow separation at the compressor inlet has been eliminated allowing proper installation of the engine and flight testing of the aircraft. Originality/value Placement and shaping of the intake duct of a turboshaft and turboprop gas turbine engine is a common industrial problem which can be challenging when the available space is limited. The inverse-by-optimization approach based on a reduced flow model, i.e. inviscid flow based on the Euler equations, and a specification of a simple target pressure distribution constitutes an efficient method to overcome the challenge.

Modeling Approach to Calculate Redistributions of HPT-Shroud Cooling Channels Minimizing Thermal Stresses Including Some Turbine Blade Tip Effects

A numerical case study on a HPT-shroud of a medium-sized commercial engine has been carried out to investigate the heat loading and the possible redistribution (number of channels, position and exit angle) of shroud cooling channels facing the turbine blade tip. A combination of modeling vehicles was used to quantify the aerodynamics, the thermodynamics and resulting heat loads on the shroud. This includes a 1-D gas turbine performance simulation model, engineering models for cooling flow distributions and heat loads, CFD modeling of the HPT flow including some tip flow effects and the finite element modeling to calculate the temperature and stress distribution in the solid shroud. Regions with high temperatures and/or maximum thermal stresses and the potential for reduction by relocating the cooling channels at equal amounts of cooling flow were identified. Although the physics involved in the processes is much more complicated than modeled, the parametric studies gave valuable insight and quantitative results in terms of differences in shroud temperatures and thermal stresses. A complementary experimental study on shroud maintenance and service experiences (not published yet) has delivered data for model input support and comparison with the numerical results.Copyright

Engine Performance Prediction for Varied LPT Vane Geometry Utilizing Test Rig Data and Combined CFD and Cycle Models

Engine performance is a result of the interaction between individual components. Any deviation from the design geometry does not only affect the flow locally, but can also lead to significantly altered whole engine performance. Specifically for Low Pressure Turbine (LPT) vanes, erosion and subsequent refurbishment can lead to considerable changes in geometry. Following vane refurbishment, the part’s effective flow area may be measured and adjusted to meet turbine nozzle matching requirements for the engine build. Other parameters such as pressure loss and outlet flow angle are not evaluated, but rather assumed equivalent to a new part. Consequently, a large portion of vanes is rejected only after engine test, making it an expensive process.A new methodology is presented here that promises to reduce the cost of acceptance tests by predicting the performance of an engine with a refurbished vane. It follows a multi-fidelity approach involving experimental testing, zero-dimensional cycle modeling and three-dimensional Computational Fluid Dynamics (CFD).Baseline performance maps of the LPT stage with varied vane geometries are generated using CFD. The obtained performance maps are incorporated into an engine cycle model. A multiple map feature for the cycle model was developed for this purpose. It enables accessing a plurality of stored maps representing a single LPT. Using performance parameters derived from test data of the isolated vane, a performance map is generated through interpolation of the baseline maps. The expected engine performance can now be readily predicted, and a well-founded decision on acceptance of the refurbished vane made.Copyright

Labyrinth Seal Technology Within the Dutch Aero Engine Cluster

Labyrinth honeycomb seals are regarded as very mature technology and seal flow performance improvements seem to be hardly achievable. However, since computational fluid dynamics have been successfully applied on the flow simulation through these seals, further seal performance optimization becomes within reach against acceptable development costs. This paper describes a staggered labyrinth seal design and is referenced against a two-knife edge stepped seal. Both seals have been evaluated with 3D CFD and tested in an advanced seal test rig facility under realistic conditions. The work described was done by the Dutch Aero Engine Cluster DAEC within the IMPACT-project for Improved Performance by Advanced Compressor Technology. The staggered seal has been selected initially based on potential performance gains, insensitive to axial excursion, good manufacturability, and robust design at acceptable development and manufacturing costs. The staggered labyrinth seal showed a performance improvement of over 30% compared with the baseline two knife edge stepped labyrinth seal. This was demonstrated by both, CFD-analyses and rig testing. In addition, the CFD and test data are consistent with each other.Copyright