Numerical Investigation of Loss Development in a Low-Pressure Turbine Cascade With Unsteady Inflow and Varying Inlet Endwall Boundary Layer

An investigation of endwall loss development is conducted using the T106A low-pressure turbine cascade. (U)RANS simulations are complemented by measurements under engine relevant flow conditions (M2th = 0.59, Re2th = 2·105). The effects of unsteady inflow conditions and varying inlet endwall boundary layer are compared in terms of secondary flow attenuation downstream of the blade passage, analyzing steady, time-averaged, and time-resolved flow fields. While both measures show similar effects in the turbine exit plane, the upstream loss development throughout the blade passage is quite different. A variation of the endwall boundary layer alters the slope of the axial loss generation beginning around the midpoint of the blade passage. Periodically incoming wakes, however, cause a spatial redistribution of the loss generation with a premature loss increase due to wake interaction in the front part of the passage followed by an attenuation of the profile- and secondary loss generation in the aft section of the blade passage. Ultimately, this leads to a convergence of the downstream loss values in the steady and unsteady inflow cases.

Dam-Break analysis: proposal of a simplified approach

ABSTRACT Simplified methods are useful alternatives for prior analysis of the effects of dam rupture and can guide the decision-making process for carrying out more complete studies. In this context, a new simplified approach is presented, which enables the analysis of aspects from dam rupture of earthen dams that failed due to overtopping, considering dam height and reservoir volume as input data. Hypothetical cases were analyzed applying dam-break hydrodynamic simulations, which results allowed the development of equations capable of estimating peak flow attenuation and peak discharge arrival time along the downstream valley. The proposed approach was applied in a hypothetical case study (15 m high dam and 17 hm3 reservoir volume), obtaining results close to those achieved through other methods, especially in case of estimating the maximum discharges throughout the downstream valley, where the average differences between the results of the methods were of the order of 15%.

Does changing connectivity due to beaver engineering result in changing hydrological function? Understanding the impacts of the return of the Eurasian beaver to Great Britain.

<p>The connectivity of landscapes is increasingly recognised as being a key control over their hydrological function and provides a valuable conceptual approach for understanding the environmental impacts of the return of beaver to European landscapes.</p><p>Beavers are the archetypal keystone species, which can profoundly alter ecosystem structure and function through their engineering activity, most notably the building of dams. Beaver dams, associated ponds and other structures such as canals can reduce downstream connectivity. However, conversely beaver engineering can also increase lateral connectivity pushing water sideways, connecting the channel and floodplain, creating complex wetland environments.</p><p>Changes in hydrological connectivity associated with beaver, has the potential to alter flow and sediment regimes, biogeochemical cycling and freshwater ecology. Results will be presented from hydrological monitoring across a range of sites in Great Britain where the Eurasian beaver (<em>Castor fiber</em>) has been reintroduced. Analysis will consider (1) does beaver engineering result in flow attenuation across scale and landuse? (2)  Is flow attenuation manifested during both low and high flow conditions?</p><p>The return of beaver to intensively managed European landscapes may provide ecosystem service benefits, including natural flood management, water quality, sediment storage and habitat creation (Puttock et al., 2017, 2018). However, beaver activity such as damming and tree felling can also cause management issues (Auster et al., 2019). Therefore, it is critical to understand where and in what density beaver damming may occur. A modelling approach will be presented for determining beaver habitat suitability and dam capacity, which in conjunction with empirical monitoring aims to provide understanding at management and policy relevant scales.</p><p>References</p><p>Auster, R. E., Puttock, A., & Brazier, R. (2019). Unravelling perceptions of Eurasian beaver reintroduction in Great Britain. Area, area.12576. https://doi.org/10.1111/area.12576</p><p>Puttock, A., Graham, H. A., Cunliffe, A. M., Elliott, M., & Brazier, R. E. (2017). Eurasian beaver activity increases water storage, attenuates flow and mitigates diffuse pollution from intensively-managed grasslands. Science of The Total Environment, 576, 430–443. https://doi.org/10.1016/j.scitotenv.2016.10.122</p><p>Puttock, A., Graham, H. A., Carless, D., & Brazier, R. E. (2018). Sediment and Nutrient Storage in a Beaver Engineered Wetland. Earth Surface Processes and Landforms. https://doi.org/10.1002/esp.4398</p>

Monitoring the efficacy of Natural Flood Management structures on flow attenuation and flood risk reduction

<p>Land use and management changes and landscape modifications, including urbanisation and agricultural intensification, have resulted in significant increases in flood risk across the UK in recent decades. To combat this, a shift towards catchment-based flood risk management has seen a marked rise in Natural Flood Management (NFM) schemes applied across the UK. These schemes largely represent mitigation strategies that work with natural processes to restore and augment hydrological and morphological catchment features for enhancing downstream flood resilience through the slowing, storing and filtering of runoff and flow. This has been implemented through the introduction of woody debris, afforestation of floodplains and runoff attenuation features. However, despite growing evidence highlighting their potential benefits, the function of these structures in the landscape and their effectiveness for flood risk reduction is still highly uncertain.</p><p> </p><p>To address this knowledge gap, this study evaluates the effectiveness of a range of larger-scale floodplain and in-channel NFM features for flow attenuation and flood risk reduction.  To achieve this, a two-year field campaign was conducted in Somerset, South West England, involving the collection of continuous discharge, storage volume and local rainfall data at four sites in the Tone and Parrett catchments. The sites contained NFM structures including offline and online storage ponds and in-channel woody debris. Using these data, filling, storing and spilling capabilities were characterised through the utilisation of field-scale DEMs from Structure from Motion (SfM) and manual surveys. Storm events were separated, and key hydrograph characteristics analysed, to determine the effect of NFM structures on high flow events and the potential for flow attenuation.</p><p> </p><p>The results indicate an increase in storage and flow attenuation as a result of the inclusion of NFM. Increases in flow lag time downstream of in-channel features were identified, relative to an upstream gauge. Longer recession limbs were also recorded downstream of storage ponds, illustrating the buffering influence of upstream structures and the consequential slowed water release downstream. Floodplain-based storage structures were found to only function optimally during the largest events, where pond filling could occur directly from the channel and flow is temporarily stored on the floodplain. These results will provide vital evidence for both local and national NFM applications.</p>

Canonical analytical solutions of wave-induced thermoelastic attenuation

SUMMARY Thermoelastic attenuation is similar to wave-induced fluid-flow attenuation (mesoscopic loss) due to conversion of the fast P wave to the slow (Biot) P mode. In the thermoelastic case, the P- and S-wave energies are lost because of thermal diffusion. The thermal mode is diffusive at low frequencies and wave-like at high frequencies, in the same manner as the Biot slow mode. Therefore, at low frequencies, that is, neglecting the inertial terms, a mathematical analogy can be established between the diffusion equations in poroelasticity and thermoelasticity. We study thermoelastic dissipation for spherical and cylindrical cavities (or pores) in 2-D and 3-D, respectively, and a finely layered system, where, in the latter case, only the Grüneisen ratio is allowed to vary. The results show typical quality-factor relaxation curves similar to Zener peaks. There is no dissipation when the radius of the pores tends to zero and the layers have the same properties. Although idealized, these canonical solutions are useful to study the physics of thermoelasticity and test numerical algorithm codes that simulate thermoelastic dissipation.

A Comparison of Three Types of Permeable Pavements for Urban Runoff Mitigation in the Semi-Arid South Texas, U.S.A

This study examines the hydrologic and environmental performance of three types of permeable pavement designs: Porous Concrete Pavement (PCP), Permeable Interlocking Concrete (PICP), and Interlocking Block Pavement with Gravel (IBPG) in the semi-arid South Texas. Outflow rate, storage, Normalized Volume Reduction (NVR), Normalized Load Reductions (NLR) of Total Suspended Solids (TSS), and Biochemical Oxygen Demand (BOD5) were compared to results obtained from adjacent traditional pavements at different regional parking lots. A notable percentage of peak flow attenuation of approximately 31–100% was observed when permeable pavements were constructed and implemented. IBPG was capable to hold runoff from rainfall depths up to 136 mm prior to flooding. PCP was the most satisfactory in reducing surface runoff (NVR: 2.81 × 10−3 ± 0.67 × 10−3 m3/m2/mm), which was significantly (p < 0.05) higher (98%) than the traditional pavement. PCP was also very effective in TSS removal (NLR: 244 × 10−5 ± 143 × 10−5 kg/m2/mm), which was an increase of over 80% removal than traditional pavement. IBPG (NLR: 7.14 × 10−5 ± 7.19 × 10−5 kg/m2/mm) showed a significantly (p < 0.05) higher (46%) BOD5 removal over traditional pavement. These results demonstrate that the type of permeable pavement and the underlying media can significantly influence the runoff reduction and infiltration in this climatic region.