Discrete Optimization on Unsteady Pressure Fluctuation of a Centrifugal Pump Using ANN and Modified GA

Pressure fluctuation due to the rotor-stator interaction in turbomachinery is unavoidable, inducing strong vibration and even shortening the lifecycle. The investigation on optimization method of an industrial centrifugal pump was carried out to reduce the pressure fluctuation intensity. Considering the time-consuming transient calculation of unsteady pressure, a novel optimization strategy was proposed by discretizing design variables and genetic algorithm. Four highly related design parameters were chosen, and 40 transient sample cases were generated and simulated using an automatic simulation program. Furthermore, a modified discrete genetic algorithm (MDGA) was proposed to reduce the optimization cost by unsteady simulation. For the benchmark test, the proposed MDGA showed a great advantage over the original genetic algorithm in terms of searching speed and could deal with the discrete variables effectively. After optimization, an improvement in terms of the performance and stability of the inline pump was achieved.

Unsteady Simulation of a Transonic Turbine Stage with Focus on Turbulence Prediction

The flow in a transonic turbine stage still poses a high challenge for the correct prediction of turbulence using an eddy viscosity model. Therefore, an unsteady RANS simulation with the k-ω SST model, based on a preceding study of turbulence inlet conditions, was performed to see if this can improve the quality of the flow and turbulence prediction of an experimentally investigated turbine flow. Unsteady Q3D results showed that none of the different turbulence boundary conditions could predict the free-stream turbulence level and the maximum values correctly. Luckily, the influence of the boundary conditions on the velocity field proved to be small. The qualitative prediction of the complex secondary flows is good, but there is lacking agreement in the prediction of turbulence generation and destruction.

Unsteady Simulation of Transonic Buffet of a Supercritical Airfoil with Shock Control Bump

The unsteady flow characteristics of a supercritical OAT15A airfoil with a shock control bump were numerically studied by a wall-modeled large eddy simulation. The numerical method was first validated by the buffet and nonbuffet cases of the baseline OAT15A airfoil. Both the pressure coefficient and velocity fluctuation coincided well with the experimental data. Then, four different shock control bumps were numerically tested. A bump of height h/c = 0.008 and location xB/c = 0.55 demonstrated a good buffet control effect. The lift-to-drag ratio of the buffet case was increased by 5.9%, and the root mean square of the lift coefficient fluctuation was decreased by 67.6%. Detailed time-averaged flow quantities and instantaneous flow fields were analyzed to demonstrate the flow phenomenon of the shock control bumps. The results demonstrate that an appropriate “λ” shockwave pattern caused by the bump is important for the flow control effect.

An Efficient Prediction Method for the Azimuthal Migration of Combustion Inhomogeneity in Multi-Stage Cooled Turbines

The outlet temperature of combustor is commonly monitored by thermocouples at the turbine exhaust. In order to establish the corresponding relationship between the temperature measured by each thermocouple and the working state of each burner, the azimuthal migration of the combustion hot/cold streaks in the multi-stage turbines needs to be quantified. Experiments to measure this migration have high cost and considerable error. It is also difficult to quantify the migration under multiple working conditions. Three-dimensional full-annulus unsteady simulation can obtain this migration. But the unsteady simulation of a single working condition could take several weeks, which is too expensive for engineering usage. A method named Steady-state Computation of Azimuthal Migration (SCAM) is proposed in this paper. By establishing and solving the transport equation of the migration angle, the azimuthal migration of hot/cold streaks can be predicted by steady-state numerical simulation using the mixing plane at rotor-stator interface. The migration computed by this method is compared with the full-annulus unsteady simulation results in multiple working conditions. The results of SCAM method show good agreement with full-annulus simulations, while costing only 0.01% of the CPU hours. It is also found that the error of SCAM is mainly caused by the fixed boundary value at coolant source terms. The optimal spanwise location of the thermocouples at turbine exhaust is discussed based on the results. The method proposed could be applied to the fault diagnosis and precise repair of the combustors of gas turbines.

Making use of our data

Engineers are acquiring data at an ever-increasing rate: data from computational design studies; measurements data from manufacturing processes, development tests, and products in service; contemporary data and legacy data. In this paper, two recommendations are made to allow engineers to make better use of these expanding databases. First, we should build on the hierarchical nature of our data; we can navigate and filter the database using high level descriptors such as design specifications and performance metrics, and then request comparative plots of detailed data such as line, contour and surface plots. Second, we can speed up the rate at which we learn from data by making the visualisations dynamic; in so doing, we enable virtual experiments to be performed that highlight connections between input parameters, output metrics and physical mechanisms. The embodiment of these two principles in the open source project, dbslice, is described. Three example applications (an aerodynamic design study for a compressor stator; the application of machine learning to aid navigation of large databases; and visualisation of a database of snapshots from an unsteady simulation) are presented. In each case, the hierarchical data and dynamic visualisations allow the user to explore the database and experience the connections and patterns within it. By Making Use of Our Data to interactively navigate existing and new design spaces in this way, engineers can accelerate their response to the challenges of future products.

Unsteady simulation of tonal noise from isolated centrifugal fan

In this study, an isolated centrifugal fan is investigated for the aerodynamic and acoustic performances usingRANS and URANS simulations. The noise is predicted by coupling the URANS and the Ffowcs Williams andHawkings acoustic analogy. The aerodynamic properties obtained from RANS and URANS are consistentwith the experimental data. The magnitudes of the tonal noise at the blade passing frequencies are wellpredicted. Recirculating flows, which are responsible for reducing the fan efficiency and increasing the noisegeneration, are observed between the shroud and the blade trailing edges. It is found that the recirculatingflows are associated with the gap between the shroud and the inlet duct.

An Optimized and Scalable Algorithm for the Fast Convergence of Steady 1-D Open-Channel Flows

Calculating an open-channel steady flow is of main interest in many situations; this includes defining the initial conditions for the unsteady simulation or the computation of the water level for a given discharge. There are several applications that require a very short computation time in order to envisage a large number of runs, for example, uncertainty analysis or optimization. Here, an optimized algorithm was implemented for the fast and efficient computation of a 1-D steady flow. It merges several techniques: a pseudo-time version of the Saint-Venant equations, an evolutionary domain and the use of a non-linear Krylov accelerator. After validation of this new algorithm, we also showed that it performs well in scalability tests. The computation cost evolves linearly with the number of nodes. This was also corroborated when the execution time was compared to that obtained by the non-linear solver, CasADi. A real-world example using a 9.5 km stretch of river confirmed that the computation times were very short compared to a standard time-dependent computation.