News
Techsburg, AFRL, and Dassault Systèmes to present paper at 2025 ASME IGTI Turbo Expo June 16-20 in Memphis, TN entitled "Simulation Approach for High-lift, High-work Low Pressure Turbine Aerodynamics Using the Lattice-Boltzmann Method"
A simulation approach was established for the application of lattice-Boltzmann method (LBM) CFD to low pressure turbine (LPT) aerodynamics for 2.5D linear cascades of LPT airfoils at low Reynolds numbers. This methodology was evaluated for six LPT airfoil geometries developed at AFRL (four high-lift, two high-lift/high-work) over realistic Reynolds lapse ranges. Predicted loss, loading, and suction surface boundary layer state were compared against prior linear cascade wind tunnel measurements acquired in the AFRL Low Speed Wind Tunnel Facility.
The chief computational strategy for the LBM simulations was to achieve direct numerical simulation (DNS)-level fidelity across the Reynolds range using LBM-LES, as implemented in the PowerFLOW® commercial solver developed by Dassault Systèmes SIMULIA Corporation. This DNS-level fidelity was achieved by maintaining isotropically-fine near-wall grid spacing (x+, y+, z+<1) across the Reynolds number range, and was demonstrated with a grid sensitivity study and the calculation of established grid resolution quality metrics for scale-resolving simulations. Recent enhancements to PowerFLOW®’s subgrid turbulence model were leveraged to achieve accurate predictions of laminar separation/reattachment.
Particular attention was paid to capturing the sensitivity of LPT airfoil cascade performance to freestream turbulence, accomplished via the introduction of resolved turbulence at the inlet of the LBM computational domain. Despite the DNS-level fidelity that was achieved, overall computational cost was compatible with industrial LPT airfoil design cycles, owing to careful scaling of the 2.5D span and simulation physical time as a function of Reynolds number. Several challenges were identified, including the occurrence of Reynolds lapse hysteresis for certain airfoils and relatively higher computational cost at the highest Reynolds numbers studied.
Techsburg and Solar Turbines to present paper at 2025 ASME IGTI Turbo Expo June 16-20 in Memphis, TN entitled "Evaluation of Lattice-Boltzmann Method Simulations for a 1-1/2 Stage Transonic Turbine with an Aggressive Interturbine Transition Duct"
The predictive accuracy of the lattice-Boltzmann method very large eddy simulation (LBM-VLES) approach was evaluated for a 1-1/2 stage transonic turbine with an aggressive interturbine transition duct (ITD). As the geometry was not publicly available, efforts were undertaken to reverse engineer the geometry of the transonic high pressure turbine (HPT) and the low pressure (LP) vane of the Transonic Test Turbine rig at the Institute for Thermal Turbomachinery at Graz University of Technology in Styria, Austria in its single HP stage aero design point (ADP1), aggressive ITD (C4) configuration. The reverse engineering process was guided by conducting steady Reynolds-Averaged Navier-Stokes (RANS) simulations using the ANSYS CFX® solver with the goal of matching published bulk performance metrics and radial flow distributions for this rig.
The unsteady LBM-VLES simulation approach (implemented using the commercial PowerFLOW®: solver developed by Dassault Systèmes Simulia Corp.) involved documenting the sensitivity of calculated bulk performance to the grid resolution, with the cell count varying from 245 million to 1.2 billion voxels (Cartesian grid elements). Particular attention was paid to grid refinement within the tip gap of the unshrouded HP blades and the evolution of resolved turbulence along the ITD shroud as the tip leakage vortices propagated downstream. Two different HP blade tip gaps were simulated (1.5% and 2.4% of the blade span), and the sensitivity to the varying tip gap was evaluated in terms of flow field evolution through the ITD and downstream LP vane row, with comparisons against RANS simulations and published rig test data. LBM-VLES simulations also identified the occurrence of an HP vane wake/blade interaction-based secondary flow mechanism, and simulation results related to this secondary flow mechanism agreed with prior experimental observations and measurements through the ITD and LP vane exit plane.
Overall, the authors found that LBM-VLES simulations were a suitable approach for predicting the performance and unsteady loss mechanisms of a 1-1/2 stage transonic turbine coupled to an aggressive ITD, at a computational cost compatible with industrial design cycles. To the authors’ knowledge, this publication represents a novel application of the lattice-Boltzmann method, in terms of both the transonic operating regime of the HP stage and its coupling to an aggressive ITD.
Techsburg, AVEC, and Virginia Tech to present paper at The Vertical Flight Society’s 81st Annual Forum May 20-22 in Virginia Beach, VA entitled "Experimental and Numerical Acoustic Scaling Investigation of a Low Tip Speed eVTOL Proprotor in Hover"
This paper shares results from work carried out during a NASA Phase I STTR project led by Technology in Blacksburg, Inc. (Techsburg, Inc): "Acoustics and Performance Scaling of a Low-Noise Tiltrotor for Urban Air Mobility Applications" (NASA Contract 80NSSC23PB607). Team partners were AVEC, Inc. and Virginia Tech, and this project follows work by Fleming, et. al. (2022), documenting results for a 5-blade low-noise proprotor measured outdoors at the Virginia Tech Drone Cage. The paper for VFS Forum 81 will share recent acoustic and aerodynamic hover experimental results for geometrically-identical 18-inch and 36-inch diameter proprotors, and compare to PowerFLOW aeroacoustic simulation results for 18-inch, 36-inch, and 90-inch diameter proprotors operating in the presence of atmospheric turbulence. The NASA Phase I STTR included testing and simulation studies in relevant wind environments, with comparison of outdoor testing to more controlled wind tunnel testing as well as the effects of geometric scaling. Proprotor geometry and test data are available to the eVTOL community to support validation efforts for prediction tools. Aerodynamic and narrowband acoustic data was shared with NASA as a Phase I deliverable for the 18-inch and 36-inch diameter sizes.