Experimental and Numerical Analysis of a Compressor Stage under Flow Distortion

On many occasions, fan or compressor stages have to face azimuthal flow distortion at inlet, which affects their performance and stability. These flow distortions can be caused by external events or by some particular geometrical features. The aim of this work is to propose a joined numerical and experimental analysis of the flow behavior in a single axial compressor stage under flow distortion. The distortions are generated by different grids that are placed upstream to the rotor. Experimentally, the flow analysis is based on the measurements obtained by a series of unsteady pressure sensors flush-mounted at the casing of the machine rotor. URANS computations are conducted using the elsA software. The flow distortion is simulated by a drop of stagnation pressure ratio at the inlet boundary condition. The study is focusing first on the ability of a pressure drop, imposed as an inlet boundary condition in CFD, to reproduce accurately the effect of a flow distortion. The analysis is conducted using singular value decomposition (SVD) and dynamic mode decomposition (DMD). A special attention is then paid, on the experimental level, to the arising of rotating stall, from the onset of the instability up to completely developed stall cells.

Accurate Inlet Boundary Conditions to Capture Combustion Chamber and Turbine Coupling with Large-Eddy Simulation

The coupling between different components of a turbomachinery is becoming more widely studied especially by use of Computational Fluid Dynamics. Such simulations are of particular interest especially at the interface between a combustion chamber and a turbine, for which the prediction of the migration of hotspots generated in the chamber is of paramount importance for performance and life-duration issues. The objective of the present study is to investigate available solutions to perform isolated simulations while taking into account the effect of multi-component coupling. Investigations presented in the paper focus on the FACTOR configuration. The fist step of the proposed method is to record conservative variables solved by the LES code at the interface plane between the chamber and the turbine of a reference simulation. Then, using the Spectral Proper Orthogonal Decomposition method, the recorded data is analysed and can be partially reconstructed using different numbers of frequencies. Using the partial reconstructions, it is then possible to replicate a realistic inlet boundary condition for isolated turbine simulations with both velocity and temperature fluctuations, while reducing the storage cost compared to the initial database. The integrated simulation is then compared to the isolated simulations as well as against simulations making use of averaged quantities with or without synthetic turbulence injection at their inlet. The isolated simulations for which the inlet condition is reconstructed with a large number of frequencies show very good agreement with the fully integrated simulation compared to the typical isolated simulation using average quantities at the inlet.

The Effect of Inlet Conditions on Turbine Endwall Loss

There can be significant variation and uncertainty in the flow conditions entering a blade row. This paper explores how this variability can affect endwall loss in axial turbines. A computational study of three cascades with collinear inlet boundary layers is conducted. Endwall loss varies by more than a factor of 3 depending on the inlet conditions. This variation is caused by dissipation of Secondary Kinetic Energy (SKE). The results can be understood by observing that the inlet conditions predominantly control how secondary vorticity is distributed within the blade passage. Modestly-thick inlet boundary layers with high shape factor tend to displace vorticity towards the center of the passage. This displacement reduces vorticity cancellation, increasing secondary velocities and SKE. A general method is formulated to estimate SKE in preliminary design. Optimum aspect ratio is shown to depend on the inlet boundary condition. Strategies to reduce endwall loss and minimize sensitivity to inlet conditions are then highlighted.

Aerodynamics Analysis of a Slotted A4412 Wind Turbine Airfoil Using CFD / Case Two

The static pressure, dynamic pressure and velocity magnitude are important parameters and have a strong influence on airfoil lift force. In this paper a slotted NACA4412 airfoil profile is considered for analysis by using the commercial code ANSYS-FLUENT 14.5® at an inlet boundary condition of different approaching wind velocities for various airfoil angles of attack in the range 0?to 24?. Renormalized group (RNG) k-? turbulence model with enhanced wall function is used for the analysis due its’ wide usage in the aerodynamic industry. Variations of the physical properties like static pressure, dynamic pressure and velocity magnitude are plotted in form of contours and/or vectors. The main aim of the research is to find out a method to enhance the efficiency of the selected airfoil and its’ workability in a wide range of low and high wind speeds which might make it suitable for installation and operation in different climates.This feasibility of enhancing the lift is and/or minimizing the drag is done by CFD on a series of independently modified NACA4412 airfoils. The current one is called Case 2. The analysis output of Case 2 is not encouraging. It does not show any improvement in NACA4412 airfoil efficiency and therefore it is classified as (obsolete).

Design and Performance of a Boundary Layer Ingesting Fan

A Boundary Layer Ingesting fan is designed to function in a tail cone thruster configuration on an existing aircraft. This means that the fan ingests part of the boundary layer developing over the fuselage all around the circumference. While the fuselage drag induced on the ingested flow makes it possible to obtain a higher propulsive efficiency, it also means that the fan will operate in a severely distorted flow. In the configuration studied here the incoming flow will generally have a lower impulse near the hub, but also substantial non-axisymmetric components. The incoming flow profile is evaluated from a CFD model of a complete Fokker 100 aircraft modified with a tail cone thruster installed. Having the aircraft modeled in detail allows the extraction of the flow entering the fan inlet, which makes up the inlet boundary condition to design for. In order to make a rational design of the fan, the incoming flow is circumferentially averaged at each radial location to form the radial profile used in the design. A fan map is created to evaluate critical points in the operating envelope in order to demonstrate that the given design is stable in operation. Operation of the fan in static ground conditions is within the operating envelope of the fan without variable nozzle area.

Commissioning of a Combined Hot-Streak and Swirl Profile Generator in a Transonic Turbine Test Facility

By enhancing the premixing of fuel and air prior to combustion, recently developed lean-burn combustor systems have led to reduced NOx and particulate emissions in gas turbines. Lean-burn combustor exit flows are typically characterized by nonuniformities in total temperature, or so-called hot-streaks, swirling velocity profiles, and high turbulence intensity. While these systems improve combustor performance, the exiting flow-field presents significant challenges to the aerothermal performance of the downstream turbine. This paper presents the commissioning of a new fully annular lean-burn combustor simulator for use in the Oxford Turbine Research Facility (OTRF), a transonic rotating facility capable of matching nondimensional engine conditions. The combustor simulator can deliver engine-representative turbine inlet conditions featuring swirl and hot-streaks either separately or simultaneously. To the best of our knowledge, this simulator is the first of its kind to be implemented in a rotating turbine test facility.The combustor simulator was experimentally commissioned in two stages. The first stage of commissioning experiments was conducted using a bespoke facility exhausting to atmospheric conditions (Hall and Povey, 2015, “Experimental Study of Non-Reacting Low NOx Combustor Simulator for Scaled Turbine Experiments,” ASME Paper No. GT2015-43530.) and included area surveys of the generated temperature and swirl profiles. The survey data confirmed that the simulator performed as designed, reproducing the key features of a lean-burn combustor. However, due to the hot and cold air mixing process occurring at lower Reynolds number in the facility, there was uncertainty concerning the degree to which the measured temperature profile represented that in OTRF. The second stage of commissioning experiments was conducted with the simulator installed in the OTRF. Measurements of the total temperature field at turbine inlet and of the high-pressure (HP) nozzle guide vane (NGV) loading distributions were obtained and compared to measurements with uniform inlet conditions. The experimental survey results were compared to unsteady numerical predictions of the simulator at both atmospheric and OTRF conditions. A high level of agreement was demonstrated, indicating that the Reynolds number effects associated with the change to OTRF conditions were small. Finally, data from the atmospheric test facility and the OTRF were combined with the numerical predictions to provide an inlet boundary condition for numerical simulation of the test turbine stage. The NGV loading measurements show good agreement with the numerical predictions, providing validation of the stage inlet boundary condition imposed. The successful commissioning of the simulator in the OTRF will enable future experimental studies of lean-burn combustor–turbine interaction.

Inlet and Outlet Characteristics Boundary Conditions for Large Eddy Simulations of Turbomachinery

Inlet an outlet boundary conditions are essential elements of any CFD predictions and this is even more so for turbomachinery Large Eddy Simulations, either applied to academic or industrial configurations. For compressible solvers, non-reflecting, characteristic inlet boundary condition imposing total pressure, total temperature and flow direction is usually needed, while an outlet relaxation methodology that automatically adapts the outlet static pressure as a function of the desired mass-flow rate rate is used for turbomachinery flow predictions. Establishing such a framework is clearly desirable especially for industrial use of LES. Development and validations remain necessary in such a fully unsteady context as detailled hereafter.