COMPARISON OF UNSTEADY REYNOLDS-AVERAGED NAVIER-STOKES PREDICTION OF SELF-PROPELLED CONTAINER SHIP SQUAT AGAINST EMPIRICAL METHODS AND BENCHMARK DATA

The demand to increase port throughput has driven container ships to travel relatively fast in shallow water whilst avoiding grounding and hence, there is need for more accurate high-speed squat predictions. A study has been undertaken to determine the most suitable method to predict container ship squat when travelling at relatively high speeds (Frh ≥ 0.5) in finite water depth (1.1 ≤ h/T ≤ 1.3). The accuracy of two novel self-propelled URANS CFD squat model are compared with that of readily available empirical squat prediction formulae. Comparison of the CFD and empirical predictions with benchmark data demonstrates that for very low water depth (h/T < 1.14) and when Frh < 0.46; Barass II (1979), ICORELS (1980), and Millward’s (1992) formulae have the best correlation with benchmark data for all cases investigated. However, at relatively high speeds (Frh ≥ 0.5) which is achievable in deeper waters (h/T ≥ 1.14), most of the empirical formulae severely underestimated squat (7-49%) whereas the quasi-static CFD model presented has the best correlation. The changes in wave patterns and effective wake fraction with respect to h/T are also presented.

FLOW PHYSICS DURING SURGE AND RECOVERY OF A MULTI-STAGE HIGH-SPEED COMPRESSOR

Stall followed by surge in a high-speed compressor can lead to violent disruption of the flow, damage to the blade structures and eventually engine shutdown. Knowledge of unsteady blade loading during surge is crucial for compressor design such as axial gap optimisation. The aim of this paper is to demonstrate the feasibility of using 3D full assembly URANS CFD for modelling surge cycles of an 8-stage high-speed compressor rig. Results from this work show stalling of the mid-stages is the surge trigger. During the flow reversal, a strong acoustic reflection occurs when the convected entropy perturbations reach the intake opening, which increase the blade loading significantly. During recovery, a hysteresis loop was recorded due to hot air reingestion, which led to a strong shear at mid-span of the IGV/R1 domain and the formation of rotating helical flow structures. The final phase of recovery was accompanied by a 4-cell multi-row tip rotating stall, which was cleared as the compressor recovered to the forward flow characteristic. It was also shown that the single passage model, despite its limitations and shortcomings in modelling recovery, can provide reasonably accurate transient flow features during surge and thus considerable insight to the flow behaviour, which can be used to obtain a first approximation of casing and blade loading.

Flow Physics During Surge and Recovery of a Multi-Stage High-Speed Compressor

Stall followed by surge in a high-speed compressor can lead to violent disruption of the flow, damage to the blade structures and eventually engine shutdown. Knowledge of unsteady blade loading during surge is crucial for compressor design such as axial gap optimisation. The aim of this paper is to demonstrate the feasibility of using 3D full assembly URANS CFD for modelling surge cycles of an 8-stage high-speed compressor rig. Results from this work show stalling of the mid-stages is the surge trigger. During the flow reversal, a strong acoustic reflection occurs when the convected entropy perturbations reach the intake opening, which increase the blade loading significantly. During recovery, a hysteresis loop was recorded due to hot air reingestion, which led to a strong shear at mid-span of the IGV/R1 domain and the formation of rotating helical flow structures. The final phase of recovery was accompanied by a 4-cell multi-row tip rotating stall, which was cleared as the compressor recovered to the forward flow characteristic. It was also shown that the single passage model, despite its limitations and shortcomings in modelling recovery, can provide reasonably accurate transient flow features during surge and thus considerable insight to the flow behaviour, which can be used to obtain a first approximation of casing and blade loading.

Comparison of Unsteady Reynolds-Averaged Navier-Stokes Prediction of Self-Propelled Container Ship Squat Against Empirical Methods and Benchmark Data

The demand to increase port throughput has driven container ships to travel relatively fast in shallow water whilst avoiding grounding and hence, there is need for more accurate high-speed squat predictions. A study has been undertaken to determine the most suitable method to predict container ship squat when travelling at relatively high speeds (Frh ≥ 0.5) in finite water depth (1.1 ≤ h/T ≤ 1.3). The accuracy of two novel self-propelled URANS CFD squat model are compared with that of readily available empirical squat prediction formulae. Comparison of the CFD and empirical predictions with benchmark data demonstrates that for very low water depth (h/T < 1.14) and when Frh < 0.46; Barass II (1979), ICORELS (1980), and Millward’s (1992) formulae have the best correlation with benchmark data for all cases investigated. However, at relatively high speeds (Frh ≥ 0.5) which is achievable in deeper waters (h/T ≥ 1.14), most of the empirical formulae severely underestimated squat (7-49%) whereas the quasi-static CFD model presented has the best correlation. The changes in wave patterns and effective wake fraction with respect to h/T are also presented.

Comparison of a closed-loop control by means of high-fidelity and low-fidelity coupled CFD/RBD computations

This work compares the principle of a basic fin-controlled sounding rocket with coupled computational fluid dynamic and rigid body dynamic simulations of two coupling environments: (1) a low-fidelity approach using Missile DATCOM as semi-empirical aerodynamic solver, and (2) a high-fidelity approach using DLR TAU as URANS CFD code. The flight mechanics solver REENT is used in both cases. A closed-loop flight path control is developed and adjusted via low-fi simulations and then verified via high-fi simulations. For simple roll and pitching maneuvers the environments match well, whereas differences can be seen in complex maneuvers, e.g. body–body interactions of separation procedures.

Experimental and Numerical Analysis on Flow Characteristics in a Double Helix Screw Pump

Experimental overall performances on a double helix screw pump are presented and discussed, focusing on the leakage flow for two different rotational speeds. A comparison between experimental and URANS CFD approaches is performed in order to check the CFD closure models’ validity. Some specific local flow characteristics are extracted from the numerical results which give explanations about leakage backflows inside the screws and local distortion at the pump inlet section.

Analysis of Gas Turbine Rim Cavity Ingestion With Axial Purge Flow Injection

Turbine rim cavities require an adequate supply of cooling purge flow to prevent hot gas ingestion from overheating metal components beneath the gas path airfoils. Purge flow is typically introduced into rim cavities through a labyrinth seal at the inner diameter of the cavity, or through conduits in the metal walls of the rim cavity. This numerical study will focus on purge flow introduced through axial holes in the stationary side of a turbine realistic rim cavity. Three dimensional Unsteady Reynolds-average Navier-Stokes (URANS) CFD modeling is utilized to model of cavity sealing effectiveness as a function of axial purge flow rate. CFD modeling is compared with experimental data from the test turbine in the Steady Thermal Aero Research Turbine (START). Results show good agreement with experimental data, especially at lower purge flow rates. Analytical depictions of the flow field setup in the rim cavity are provided, explaining trends observed in experimental data. Differences in sealing effectiveness trends between the upper and lower portions of the rim cavity are predicted by CFD modeling, adding insight to ingestion phenomena in turbine realistic rim cavities with complex geometry and flow leakage paths.