Fan propeller blades gain superior aerodynamic efficiency with computational fluid dynamics

 Stockholm 10 Apr 99 Producers and designers of fans and propellers are permanently in search of shape optimization for blade design. Both the aerospace sector and the metallurgical, chemical and engineering industries constitute important end users of propellers, fans, compressors and turbines while large volumes of the smallest fan units are required by the electronics industry. All of these customers demand better blade shape design in order to lower the product's weight, decrease the noise and reduce the costs for validation procedures. In this regard, a prototype software system for aerodynamic shape optimization is being developed in the OPTIBLADE project. The OPTFLO programme has to demonstrate the suitability of High Performance Computing techniques for parametric optimization using automatic differentiation applied to the design of fan and propeller blades profiles.

Manufacturers from aerospace and machinery industry have joined forces with engineering consultants, academic researchers, and computing centres to develop the pilot software OPTFLO to shorten the design cycle of fans and propellers, to improve the product quality, and to allow better customization. The programme exploits the latest discoveries in optimization algorithms and also applies automatic differentiation for the parameterization of the blade shape design concepts. The partners can dispose of cost-effective high performance computers (HPC) in order to run the required flow simulations. Within OPTIBLADE, the Navier Stockes Multi Block (NSMB) flow solver is parallelized and is able to scale up to over 100 processors for large calculation problems.

Aerodynamic optimization still includes a huge number of flow simulations. The OPTFLO modelling tool has the capacity to reduce the amount of flow simulations, needed to obtain a design. The software is based on existing packages for Computational Fluid Dynamics and parametric differentiation and optimization. The NSMB parallel multi-block flow solver is provided by the Swiss Federal Institute of Technology (EPFL) and is already successfully used in an industry-academia consortium with Aérospatiale, SAAB, Cerfacs, and the Swedish Royal Institute of Technology (KTH). Parallel CFD or computational fluid dynamics is complemented by the parametric solution technique, developed by CADOÉ in the ADO software system. This programme offers speed advantages and efficient use of parallel computers in order to explore the adequate parameter space for optimization.

illustration
Optimization of propeller blade design

The OPTFLO optimization procedure consists of three steps, which are the pre-processing, the solution, and the post-processing stages. As for the pre-processing phase, the designer has to perform the four tasks of building the geometry, prescribing the boundary conditions, meshing the geometry, and defining the design parameters. An external programme (nsmbP) executes the solution phase. The post-processing phase involves the plotting of the evolution within the distinctive criteria, including the maximum of velocity modulus, the mach number, the static pressure, the total temperature, and so on. This task is accomplished according to the variations of a pre-set parameter. In order to evaluate the quality of the OPTFLO software tool, the OPTIBLADE partners plan demonstrations on three industrially relevant test cases.

illustration
Processing phase

With better blade shapes, major elements such as the power consumption, the motor size and noise level, the installation, adaptability and serviceability of propeller and fan systems can be substantially improved. The OPTFLO tool will therefore be tested by the ABB Fans company in the production of blades for reversible fans; by Ratier-Figeac, a French provider of high speed propellers for passenger aircrafts; and by Liebherr-Aerospace in the design of turbine wheels for cabin pressurization equipment. Once the design software has been industrially validated, OPTFLO will play a key role in the process of shortening the optimization design time since the large number of physical prototypes can be reduced. The commercial implementation of OPTFLO will result in more careful designs at competitive prices and with better balanced trade-offs.

For more information, check in at the OPTIBLADE project web site.

Leslie Versweyveld