Numerical Tool Optimization for Advanced Rocket Nozzle Performance Prediction

A number of Altitude-Compensating Nozzle concepts have been developed through the years, to reduce nozzle performance losses. One of the most promising concepts is the dual- bell nozzle, where the flow is capable of auto-adapting at low and high altitude without the use of mechanical devices. This paper focuses on the optimization and validation of an in- house solver for the prediction of the flow field in advanced rocket nozzles, with emphasis on dual-bell rocket nozzles. Numerical efforts are concentrated on predicting transition from one operating mode to the other, since low and high altitude operating modes are both well known stable conditions. Both steady state and transient problems are considered and the performances of different numerical schemes are investigated

A Numerical Smith Diagram Revision for Modern Low Pressure Turbine Profiles

Smith diagram is historically one of the standard tools used for turbine design, especially in concept design phase (CD) and for assessment/comparison of turbine configurations. For each turbomachinery stage, this graph provides a relation among stage loading factor (y), flow coefficient (f) and aerodynamic performance (). However, various essential inputs such as stage reactions (R), aspect ratios (AR) or Reynolds numbers (Re), or outputs like flow deflections (d), profile weights and stresses are not directly taken into account. In the work here presented, traditional loss correlation models (Craig & Cox (C&C) and Ainley & Mathieson, Dunham & Came, Kacker & Okapuu (AMDCKO)), are used to evaluate stage performance and then to derive a more complete vision of key parameters. Starting from a representative turbine configuration, once some main characteristic boundary conditions (BC) have been defined, few parameters are changed in order to obtain a stage operating in a specific region of the Smith diagram. By this way, it has been possible to compare experimental data from original Smith with computational results obtained with such approach. Moreover, additional details previously missing (both aerodynamic and mechanical) have been obtained and optimal design considerations have been investigated under a multidisciplinary point of view. In addiction, by means of dedicated tools, blade geometries have been prepared for some of these configurations. Some preliminary CFD 3D analyses have then been run to improve specific understandings. This research leads to extend Smith diagram with many other important information for turbine module design and to numerically revise the diagram itself, adjusting it with data coming from modern high performance profile’s analyses

Free-stream turbulence effects on the boundary layer of a high-lift Low-Pressure-Turbine blade

The suction side boundary layer evolution of a high-lift low-pressure turbine cascade has been experimentally investigated at low and high free-stream turbulence intensity conditions. Measurements have been carried out in order to analyze the boundary layer transition and separation processes at a low Reynolds number, under both steady and unsteady inflows. Static pressure distributions along the blade surfaces as well as total pressure distributions in a downstream tangential plane have been measured to evaluate the overall aerodynamic efficiency of the blade for the different conditions. Particle Image Velocimetry has been adopted to analyze the time-mean and time-varying velocity fields. The flow field has been surveyed in two orthogonal planes (a blade-to-blade plane and a wall-parallel one). These measurements allow the identification of the Kelvin-Helmholtz large scale coherent structures shed as a consequence of the boundary layer laminar separation under steady inflow, as well as the investigation of the three-dimensional effects induced by the intermittent passage of low and high speed streaks. A close inspection of the time-mean velocity profiles as well as of the boundary layer integral parameters helps to characterize the suction side boundary layer state, thus justifying the influence of free-stream turbulence intensity on the blade aerodynamic losses measured under steady and unsteady inflows