This presentation was made at the NAFEMS European Conference on Simulation-Based Optimisation held on the 15th of October in London.
Optimisation has become a key ingredient in many engineering disciplines and has experienced rapid growth in recent years due to innovations in optimisation algorithms and techniques, coupled with developments in computer hardware and software capabilities. The growing popularity of optimisation in engineering applications is driven by ever-increasing competition pressure, where optimised products and processes can offer improved performance and cost-effectiveness which would not be possible using traditional design approaches. However, there are still many hurdles to be overcome before optimisation is used routinely for engineering applications.
The NAFEMS European Conference on Simulation-Based Optimisation brings together practitioners and academics from all relevant disciplines to share their knowledge and experience, and discuss problems and challenges, in order to facilitate further improvements in optimisation techniques.
Unified Brands, a division of Dover Company, offers continuous motion ware-washing systems to maximize cleaning power and give commercial kitchens an advantage in performance and versatility. The ware-washing system consists of a centrifugal pump, a discharge manifold with multiple jets and a wash tank with provision for recirculating the wash fluid. In this paper, design and optimization of the discharge manifold to achieve uniform flow distribution using computational fluid dynamics simulations is discussed.
To achieve this objective, steady-state 3D simulations were initially carried out for the baseline model where the measured flow rate data was available at the exit of the jet for validation. The computational model consisted of the discharge manifold with twelve lateral jet outlets and the wash tank. A volume-flow profile was used as the inlet boundary condition at the inlet of the discharge manifold. This profile was obtained from a stand-alone analysis of the centrifugal pump. The surface that connects the wash tank to the pump inlet was specified as the pressure outlet boundary. In the analysis, it was assumed that there is no cavitation and there is no sloshing of water in the tank. In order to capture the effect of turbulence, a standard k- model with scalable wall function was used. Through this simulation of the baseline model, the flow rates at the exits of the jets were obtained. These predicted flow rates at the exits of jets were within ±5% of the measured values. Also, the trend of flow rate from the first jet to the last jet of the manifold matched the test data.
Based on first principles, several design concepts were identified with potential to achieve uniform flow through the jets. For the selected design, a multi-objective design optimization was performed. The new design consisted of a pair of hump-like structures positioned symmetrically to the jet axes, placed at the back wall of the discharge manifold. The design parameters such as the hump diameter, number of hump pairs, position of the humps from the jet axes and manifold height were identified for parametrization. The minimum to maximum ranges of these parameters were also defined. In order to restrict the number of design points to a reasonable number, central-composite, face-centred design was used. This led to simulations for 31 design points. For optimization, four objective functions (responses) were defined: flow ratio, velocity ratio, inlet pressure ratio, and velocity difference. The response surface optimization was used to evaluate the impact of multiple input variables on the objective functions. The optimized design thus obtained was further simulated, and it confirmed that the flow distribution at all outlets was almost uniform with deviation of ±5% from the mean value. This design was further tested in the lab, and the measured flow rate at the exits of jets was within ±2.7% of the predicted values. This paper demonstrates a successful case study of utilizing computational fluid dynamics simulations and optimization to design an innovative product to solve a real-world problem.
|Date||15th October 2019|