Experimental and Numerical Investigation of Gaseous Detonation in a Narrow Channel with Obstacles

Gaseous detonation propagation in a thin channel with regularly spaced cylindrical obstacles was investigated experimentally and numerically. The wave propagation with substantial velocity deficits is observed and the details of its propagation mechanism are described based on experimental measurements of the luminosity and pressure and on three-dimensional flow fields obtained by numerical simulations. Both experiments and simulations indicate a significant role of shock–shock and shock–obstacle interactions in providing high-temperature conditions necessary to sustain the reaction wave propagation.

Wake Statistics of Different-Scale Wind Turbines under Turbulent Boundary Layer Inflow

Subscale wind turbines can be installed in the field for the development of wind technologies, for which the blade aerodynamics can be designed in a way similar to that of a full-scale wind turbine. However, it is not clear whether the wake of a subscale turbine, which is located closer to the ground and faces different incoming turbulence, is also similar to that of a full-scale wind turbine. In this work we investigate the wakes from a full-scale wind turbine of rotor diameter 80 m and a subscale wind turbine of rotor diameter of 27 m using large-eddy simulation with the turbine blades and nacelle modeled using actuator surface models. The blade aerodynamics of the two turbines are the same. In the simulations, the two turbines also face the same turbulent boundary inflows. The computed results show differences between the two turbines for both velocity deficits and turbine-added turbulence kinetic energy. Such differences are further analyzed by examining the mean kinetic energy equation.

Effect of tip spacing, thrust coefficient and turbine spacing in multi-rotor wind turbines and farms

Large eddy simulations (LESs) are performed to study the wakes of a multi-rotor wind turbine configuration comprising four identical rotors mounted on a single tower. The multi-rotor turbine wakes are compared to the wake of a conventional turbine comprising a single rotor per tower with the same frontal area, hub height and thrust coefficient. The multi-rotor turbine wakes are found to recover faster, while the turbulence intensity in the wake is smaller, compared to the wake of the conventional turbine. The differences with the wake of a conventional turbine increase as the spacing between the tips of the rotors in the multi-rotor configuration increases. The differences are also sensitive to the thrust coefficients used for all rotors, with more pronounced differences for larger thrust coefficients. The interaction between multiple multi-rotor turbines is contrasted with that between multiple single-rotor turbines by considering wind farms with five turbine units aligned perfectly with each other and with the wind direction. Similar to the isolated turbine results, multi-rotor wind farms show smaller wake losses and smaller turbulence intensity compared to wind farms comprised of conventional single-rotor turbines. The benefits of multi-rotor wind farms over single-rotor wind farms increase with increasing tip spacing, irrespective of the axial spacing and thrust coefficient. The mean velocity profiles and relative powers of turbines obtained from the LES results are predicted reasonably accurately by an analytical model assuming Gaussian radial profiles of the velocity deficits and a hybrid linear-quadratic model for the merging of wakes. These results show that a larger power density can be achieved without significantly increased fatigue loads by using multi-rotor turbines instead of conventional, single-rotor turbines.

Effect of tip spacing, thrust coefficient and turbine spacing inmulti-rotor wind turbines and farms

Large eddy simulations (LES) are performed to study the wakes of a multi-rotor wind turbine configuration comprising of four identical rotors mounted on a single tower. The multi-rotor turbine wakes are compared to the wake of a conventional turbine comprising of a single rotor per tower with the same frontal area, hub height and thrust coefficient. The multi-rotor turbine wakes are found to recover faster, while the turbulence intensity in the wake is smaller, compared to the wake of the conventional turbine. The differences with the wake of a conventional turbine increase as the spacing between the tips of the rotors in the multi-rotor configuration increases. The differences are also sensitive to the thrust coefficients used for all rotors, with more pronounced differences for larger thrust coefficients. The interaction between multiple multi-rotor turbines is contrasted with that between multiple single-rotor turbines by considering wind farms with five turbine units aligned perfectly with each other and with the wind direction. Similar to the isolated turbine results, multi-rotor wind farms show smaller wake losses and smaller turbulence intensity compared to wind farms comprised of conventional single-rotor turbines. The benefits of multi-rotor wind farms over single-rotor wind farms increase with increasing tip spacing, irrespective of the axial spacing and thrust coefficient. The mean velocity profiles and relative powers of turbines obtained from the LES results are predicted reasonably accurately by an analytical model assuming Gaussian radial profiles of the velocity deficits and a hybrid linear-quadratic model for merging of wakes. These results show that a larger planform energy flux can be achieved without significantly increased fatigue loads by using multi-rotor turbines instead of conventional, single-rotor turbines.

Wind tunnel experiments on wind turbine wakes in yaw: redefining the wake width

This paper presents an investigation of wakes behind model wind turbines, including cases of yaw misalignment. Two different turbines were used and their wakes are compared, isolating effects of boundary conditions and turbine specifications. Laser Doppler anemometry was used to scan full planes of wakes normal to the main flow direction, six rotor diameters downstream of the respective turbine. The wakes of both turbines are compared in terms of the time-averaged main flow component, the turbulent kinetic energy and the distribution of velocity increments. The shape of the velocity increments' distributions is quantified by the shape parameter λ2. The results show that areas of strongly heavy-tailed distributed velocity increments surround the velocity deficits in all cases examined. Thus, a wake is significantly wider when two-point statistics are included as opposed to a description limited to one-point quantities. As non-Gaussian distributions of velocity increments affect loads of downstream rotors, our findings impact the application of active wake steering through yaw misalignment as well as wind farm layout optimizations and should therefore be considered in future wake studies, wind farm layout and farm control approaches. Further, the velocity deficits behind both turbines are deformed to a kidney-like curled shape during yaw misalignment, for which parameterization methods are introduced. Moreover, the lateral wake deflection during yaw misalignment is investigated.

Wind tunnel experiments on wind turbine wakes in yaw: Redefining the wake width

This paper presents an investigation of wakes behind model wind turbines, including cases of yaw misalignment. Two different turbines were used and their wakes are compared, isolating effects of boundary conditions and turbine specifications. Laser Doppler Anemometry was used to scan a full plane of a wake normal to the main fow direction, 6 rotor diameters downstream of the respective turbine. The wakes of both turbines are compared in terms of the time averaged main flow component, the turbulent kinetic energy and the distribution of velocity increments. The shape of the velocity increments' distributions is quantified by the shape parameter λ2. The results show that areas of strongly heavy-tailed distributed velocity increments are surrounding the velocity deficit in all cases examined. Thus, a wake is significantly wider when two-point statistics are included as opposed to a description limited to one-point quantities. As non-Gaussian distributions of velocity increments affect loads of downstream rotors, our findings impact the application of active wake steering through yaw misalignment as well as wind farm layout optimizations and should therefore be considered in future wake studies, wind farm layout and farm control approaches. Further, the velocity deficits behind both turbines are deformed to a kidney-like curled shape during yaw misalignment, for which parameterization methods are introduced. Moreover, the lateral wake deflection during yaw misalignment is investigated.

Experimental Investigation of Fish Farm Hydrodynamics on 1:15 Scale Model Square Aquaculture Cages

Hydrodynamic drag and wake properties of square aquaculture cage arrays were studied to improve understanding of nutrient dynamics from fish cages to guide the design of integrated multitrophic aquaculture (IMTA). A 1:15 scale model array (2 × 3) of square cages was developed and deployed in a large recirculating flume tank. Drag measurements were measured for individual cages within the array relative to current velocity. Results showed the highest drag for the first row of cages, with drag reducing significantly through rows 2 and 3. A wake velocity study observed velocity deficits, wake topology, wake recovery, and turbulence in the flow fields. High-velocity deficits were measured directly behind cages within the array, causing flow to be accelerated around and below the cages. The presence of a shear layer in the wake of the cages caused high levels of turbulence downstream. These results can be used to help predict patterns of nutrients released from cages into the environment and aid in the placement of nutrient extractive species in IMTA systems.