• A non-invasive airborne wave monitor

      Nichols, Andrew; Tait, Simon J.; Horoshenkov, Kirill V.; Shepherd, Simon J. (2013)
      This work presents a new acoustical method for remote measurement of the surface characteristics of the dynamic air-water interface in turbulent free-surface flows. The technique uses the reflection of a monochromatic ultrasonic wave by the dynamically rough air-water interface to measure the water surface position. It is found that with careful selection of the acoustical components and their configuration, the phase of the reflected signal responds to the local fluctuations in the fluid interface at the point of specular acoustic reflection. In order for the method to be applicable, three criteria must be satisfied: (1) the dominant wavelength of the surface under investigation must be greater than the first Fresnel zone corresponding to the wavelength and component geometry of the acoustical system; (2) the mean magnitude of the instantaneous local surface gradient must not exceed 0.025; and (3) the root-mean-square wave height must be greater than 1% of the acoustic wavelength. Under these conditions the mean error of the system is within 5% (and usually within 1%) of the acoustic wavelength, and is generally within 10% of the wave amplitude for turbulence generated waves, and 3% of the amplitude for gravity waves. This error may be reduced by optimising the acoustic wavelength for the surface of interest. For turbulent depth limited flows, the surface waves fall well within the criteria, and the absolute errors are independent of wave height, so for larger wave heights, the relative error can be considerably lower. The technique provides a robust system for monitoring the dynamics of free surface flows, which is non-invasive, low cost, and low power. The method has been tested on laboratory flows but should be applicable to remote sensing of free surface properties on a local scale in field environments where invasive techniques are difficult to implement such as might be found in coastal, river and wastewater environments.
    • Analysis of ground-source heat pumps in north-of-England homes

      Ali, Alexis; Mohamed, Mostafa H.A.; Abdel-Aal, Mohamad; Schellart, A.; Tait, Simon J. (2016)
      The performance of Ground Source Heat Pump (GSHP) systems for domestic use is an increasing area of study in the UK. This paper examines the thermal performance of three bespoke shallow horizontal GSHP systems installed in newly built residential houses in the North of England against a control house which was fitted with a standard gas boiler. A total of 350 metres of High Density Polyethylene pipe with an external diameter of 40 mm was used for each house as a heat pump loop. The study investigated (i) the performance of a single loop horizontal Ground Heat Exchanger (GHE) against a double loop GHE and (ii) rainfall effects on heat extraction by comparing a system with an infiltration trench connected to roof drainage against a system without an infiltration trench above the ground loops. Parameters monitored for a full year from October 2013 to September 2014. Using the double GHE has shown an enhanced performance of up to 20% compared with single GHE. The infiltration trench is found to improve performance of the heat pumps; the double loop GHE system with an infiltration trench had a COP 5% higher than that of the double loop GHE system without a trench.
    • Dominant features in three-dimensional turbulence structure: comparison of non-uniform accelerating and decelerating flows

      Pu, Jaan H.; Tait, Simon J.; Guo, Yakun; Huang, Y.; Hanmaiahgari, P.R. (2018-04)
      The results are presented from an experimental study to investigate three-dimensional turbulence structure profiles, including turbulence intensity and Reynolds stress, of different non-uniform open channel flows over smooth bed in subcritical flow regime. In the analysis, the uniform flow profiles have been used to compare with those of the non-uniform flows to investigate their time-averaged spatial flow turbulence structure characteristics. The measured non-uniform velocity profiles are used to verify the von Karman constant κ and to estimate sets of log-law integration constant Br and wake parameter П, where their findings are also compared with values from previous studies. From κ, Br and П findings, it has been found that the log-wake law can sufficiently represent the non-uniform flow in its non-modified form, and all κ, Br and П follow universal rules for different bed roughness conditions. The non-uniform flow experiments also show that both the turbulence intensity and Reynolds stress are governed well by exponential pressure gradient parameter β equations. Their exponential constants are described by quadratic functions in the investigated β range. Through this experimental study, it has been observed that the decelerating flow shows higher empirical constants, in both the turbulence intensity and Reynolds stress compared to the accelerating flow. The decelerating flow also has stronger dominance to determine the flow non-uniformity, because it presents higher Reynolds stress profile than uniform flow, whereas the accelerating flow does not.
    • Effects of coolant flow rate, groundwater table fluctuations and infiltration of rainwater on the efficiency of heat recovery from near surface soil layers

      Mohamed, Mostafa H.A.; El Kezza, O.; Abdel-Aal, Mohamad; Schellart, A.; Tait, Simon J. (2015-01)
      This paper aims to investigate experimentally the effects of circulating coolant flow rate, groundwater table fluctuations, infiltration of rainwater, on the amount of thermal energy that can be recovered from the near surface soil layers. A comprehensive experimental investigation was carried out on a fully equipped tank filled with sand. A heat collector panel was embedded horizontally at the mid-height of the tank. Measurements of the temperature at various points on the heat collector panel, adjacent soil, inlet and outlet were continuously monitored and recorded. After reaching a steady state, it was observed that increasing water saturation in the adjacent soil leads to a substantial increase on the amount of heat recovered. A model was proposed for the estimation of temperature along the heat collector panel based on steady state conditions. It accounted for thermal resistance between pipes and the variability of water saturation in the adjacent soils. This model showed good agreement with the data. Whilst increasing the flow rate of the circulating fluid within the panel did not cause noticeable improvement on the amount of heat energy that can be harnessed within the laminar flow regime commonly found in ground source heat panels. Infiltration of rainwater would cause a temporary enhancement on the amount of extracted heat. Measurement of the sand thermal conductivity during a cycle of drying and wetting indicates that the thermal conductivity is primarily dependent upon the degree of water saturation and secondary on the flow path.
    • Low cost on-line non-invasive sewer flow monitoring

      Nichols, Andrew; Tait, Simon J.; Horoshenkov, Kirill V.; Shepherd, Simon J.; Zhang, Y. (2013)
      A novel acoustic sensor has been developed, capable of remotely monitoring the free surface ‘fingerprint’ of shallow flows. Temporal and spatial properties of this pattern are shown to contain information regarding the nature of the flow itself. The remote measurement can thereby be used to infer the bulk flow properties such as depth, velocity, and the hydraulic roughness of the pipe. The instrument is non-invasive and is also low cost, low maintenance, and low power. Such a device will allow for widespread monitoring of flow conditions in drainage networks, enabling pro-active maintenance and reliable real-time control.
    • Making use of turbulence and its interaction with sound: a non-invasive flow monitor

      Nichols, Andrew; Horoshenkov, Kirill V.; Tait, Simon J.; Shepherd, Simon J. (2014)
      A novel acoustic sensor has been developed which is capable of remotely monitoring the free surface ‘fingerprint’ of shallow flows. The temporal and spatial properties of this fingerprint are shown to contain a wealth of information regarding the nature of the flow itself. The remote measurement can thereby be used to infer the bulk flow properties such as depth, velocity, and hydraulic roughness to within 8 % accuracy. The instrument is totally non-invasive and as such is low cost, low maintenance, and low power. Such a device will allow for widespread monitoring of flow conditions in drainage and river networks, informing flood models, and facilitating pro-active maintenance and real time control.
    • A model of the free surface dynamics of shallow turbulent flows

      Nichols, Andrew; Tait, Simon J.; Horoshenkov, Kirill V.; Shepherd, Simon J. (2016-05-16)
      Understanding the dynamic free surface of geophysical flows has the potential to enable direct inference of the flow properties based on measurements of the free surface. An important step is to understand the inherent response of free surfaces in depth-limited flows. Here a model is presented to demonstrate that free surface oscillatory spatial correlation patterns result from individual surface features oscillating vertically as they advect over space and time. Comparison with laboratory observations shows that these oscillating surface features can be unambiguously explained by simple harmonic motion, whereby the oscillation frequency is controlled by the root-mean-square water surface fluctuation, and to a lesser extent the surface tension. This demonstrates that the observed “complex” wave pattern can be simply described as an ensemble of spatially and temporally distributed oscillons. Similarities between the oscillon frequency and estimated frequency of near-bed bursting events suggest that oscillon behaviour is linked with the creation of coherent flow structures.
    • Modeling in-sewer erosion to predict sewer flow quality

      Tait, Simon J.; Ahyerre, M.; Chebbo, G.; Skipworth, P.J. (2003)
      High levels of suspended solids are typically observed during the initial part of storms. Field evidence suggests that these suspended solids derive from the erosion of in-sewer sediment beds accumulated during dry and previous wet weather periods. Suspended sediment transport rate models within existing sewer network modeling tools have utilized inappropriate transport rate relationships developed mainly in fluvial environments. A process model that can account for the erosion of fine-grained highly organic in-sewer sediment deposits has been formulated. Values of parameters describing the increase in deposit strength with depth are required. These values are obtained using a genetic algorithm based calibration routine that ensures model simulations of suspended sediment concentrations that correspond to field data collected in a discrete length of sewer in Paris under known hydraulic event conditions. These results demonstrate the applicability of this modeling approach in simulating the magnitude and temporal distribution of suspended in-sewer sediment eroded by time varying flow. Further work is developing techniques to enable the application of this type of model at the network level.
    • Modelling the viability of heat recovery from combined sewers

      Abdel-Aal, Mohamad; Smits, R.; Mohamed, Mostafa H.A.; De Gussem, K.; Schellart, A.; Tait, Simon J. (2014-07-01)
      Modelling of wastewater temperatures along a sewer pipe using energy balance equations and assuming steady-state conditions was achieved. Modelling error was calculated, by comparing the predicted temperature drop to measured ones in three combined sewers, and was found to have an overall root mean squared error of 0.37 K. Downstream measured wastewater temperature was plotted against modelled values; their line gradients were found to be within the range of 0.9995-1.0012. The ultimate aim of the modelling is to assess the viability of recovering heat from sewer pipes. This is done by evaluating an appropriate location for a heat exchanger within a sewer network that can recover heat without impacting negatively on the downstream wastewater treatment plant (WWTP). Long sewers may prove to be more viable for heat recovery, as heat lost can be reclaimed before wastewater reaching the WWTP.
    • Predicting wastewater temperatures in sewer pipes using abductive network models

      Abdel-Aal, Mohamad; Mohamed, Mostafa H.A.; Smits, R.; Abdel-Aal, R.E.; De Gussem, K.; Schellart, A.; Tait, Simon J. (2015)
      A predictive modelling technique was employed to estimate wastewater temperatures in sewer pipes. The simplicity of abductive predictive models attracts large numbers of users due to their minimal computation time and limited number of measurable input parameters. Data measured from five sewer pipes over a period of 12 months provide 33,900 training entries and 39,000 evaluation entries to support the models' development. Two simple predictive models for urban upstream combined sewers and large downstream collector sewers were developed. They delivered good correlation between measured and predicted wastewater temperatures proven by their R(2) values of up to 0.98 and root mean square error (RMSE) of the temperature change along the sewer pipe ranging from 0.15 degrees C to 0.33 degrees C. Analysis of a number of potential input parameters indicated that upstream wastewater temperature and downstream in-sewer air temperature were the only input parameters that are needed in the developed models to deliver this level of accuracy.
    • Probabilistic modelling of bed-load composition.

      Tait, Simon J.; Heald, J.; McEwan, I.K.; Soressen, M.; Cunningham, G.; Willetts, B.; Goring, D. (2009-06-24)
      This paper proposes that the changes which occur in composition of the bed load during the transport of mixed-grain-size sediments are largely controlled by the distributions of critical entrainment shear stress for the various size fractions. This hypothesis is examined for a unimodal sediment mixture by calculating these distributions with a discrete particle model and using them in a probabilistic calculation of bed-load composition. The estimates of bed-load composition compare favorably with observations of fractional transport rates made in a laboratory flume for the same sediment, suggesting that the hypothesis is reasonable. The analysis provides additional insight, in terms of grain mechanics, into the processes that determine bed-load composition. These insights strongly suggest that better prediction methods will result from taking account of the variation of threshold within size fractions, something that most previous studies have neglected.
    • Sediment transport over a flat bed in a uni-directional flow: simulations and validation.

      Heald, J.; McEwan, I.K.; Tait, Simon J. (2004)
      A discrete particle model is described which simulates bedload transport over a flat bed of a unimodal mixed-sized distribution of particles. Simple physical rules are applied to large numbers of discrete sediment grains moving within a unidirectional flow. The modelling assumptions and main algorithms of the bedload transport model are presented and discussed. Sediment particles are represented by smooth spheres, which move under the drag forces of a simulated fluid flow. Bedload mass-transport rates calculated by the model exhibit a low sensitivity to chosen model parameters. Comparisons of the calculated mass-transport rates with well-established empirical relationships are good, strongly suggesting that the discrete particle model has captured the essential elements of the system physics. This performance provides strong justification for future interrogation of the model to investigate details of the small-scale constituent processes which have hitherto been outside the reach of previous experimental and modelling investigations.
    • Simulation of Turbulent Free Surface Obstructed Flow within Channels

      Pu, Jaan H.; Hussain, Khalid; Tait, Simon J. (2007-07-01)
      Free surface flows of practical relevance in many engineering problems are almost always turbulent. In this paper, a numerical model to compute the free surface flow with turbulent effects is presented. The shallow water equations together with a k-ε turbulent model are discretized and simulated using a MUSCL-HANCOCK finite volume scheme. The proposed 2D k-ε shallow water model calculates the depth-averaged quantities such as water depth and velocity profile. The depth-averaged turbulent viscous stresses are determined from the depthaveraged version of a traditional 3D k-ε turbulent model. The numerical model is applied to a flow within channels that contain full depth obstructions. The k-ε turbulent model results are compared with existing Direct Numerical Simulations (DNS) predictions and show a high level of accuracy.
    • The experimental and numerical approach of two-phase flows by wall jets on rough beds in open channel flow

      Ghoma, Mohamed Ibrahem; Hussain, Khalid; Tait, Simon J. (2014)
      This paper presents the results of investigations carried out to study the effect of horizontal wall jets on a fixed rough bed in an open channel. The study used both numerical and experimental approaches. The numerical and experimental studies are compared for validation. The main objective of this study is to understand the effect of wall jets on a horizontal fixed rough bed in an open channel. The experimental study investigated the effect of wall jets on a fixed horizontal bed, with a known roughness in an open channel flume. A sid-looking Acoustic Doppler Velocimetry (ADV) was used to measure the velocity profile of the flow at different flow zones. The wave monitor was used to measure the free surface during the experiments. Computational fluid dynamics CFD simulations were conducted in a rectangular channel to compare with the laboratory tests using the volume of fluid VOF multiphase method and K- ࢿ model. The two phase (water and air) was used in this study. Computer simulations for the model were used to predict the fluid horizontal velocity (u) revealing the characteristics of the wall jet over different flow zones (developing, fully developed and recovering zones). The results showed that the velocity profiles distribution in the stream wise direction in the channel were reasonable. The reverse velocity was close to the wall jet and the maximum reverse velocity was observed near the water surface. Also the results showed that the depression was close to the wall jet. The agreement between the results obtained from the numerical and the experimental data were reasonable.
    • The pattern of surface waves in a shallow free surface flow

      Horoshenkov, Kirill V.; Nichols, Andrew; Tait, Simon J.; Maximov, G.A. (2013)
      This work presents new water surface elevation data including evidence of the spatial correlation of water surface waves generated in shallow water flows over a gravel bed without appreciable bed forms. Careful laboratory experiments have shown that these water surface waves are not well-known gravity or capillary waves but are caused by a different physical phenomenon. In the flow conditions studied, the shear present in shallow flows generates flow structures, which rise and impact on the water-air interface. It is shown that the spatial correlation function observed for these water surface waves can be approximated by the following analytical expression W(rho) = e(-rho 2/2 sigma w2)COS(2 pi L-0(-1)rho). The proposed approximation depends on the spatial correlation radius, sigma(w), characteristic spatial period, L-0, and spatial lag, . This approximation holds for all the hydraulic conditions examined in this study. It is shown that L-0 relates to the depth-averaged flow velocity and carries information on the shape of the vertical velocity profile and bed roughness. It is also shown that sigma(w) is related to the hydraulic roughness and the flow Reynolds number.
    • Thermal and hydraulic properties of sandy soils during drying and wetting cycles

      Ali, Alexis; Mohamed, Mostafa H.A.; Aal, M.; Schellart, A.; Tait, Simon J. (2014)
      There is an increasing interest in the use of Ground Source Heat Pumps (GSHPs) as a source of renewable energy in temperate countries. GSHPs coupled with buried heat collectors can harness the thermal energy from near-surface soils to provide the heating required for domestic properties. The performance of a GSHP system depends greatly on the thermal conductivity of the surrounding soils. Near-surface soils undergo cycles of drying and wetting due to, for example, the infiltration of rain water and/or fluctuations of the ground water table. Several parameters - including the properties of soil, suction head and saturation history - affect the thermal properties as well as the retention and flow of water. This paper presents results from a comprehensive laboratory investigation on sand samples with markedly different grain size distribution. Simultaneous measurements of thermal and hydraulic properties of the sands were taken under incremental increase/decrease in the suction head values to simulate cycles of drying and wetting. The results clearly suggest that the thermal conductivity is better expressed as a function of the matric suction head so as to reflect the saturation history. There has been almost five-fold increase in the measured value of thermal conductivity when the soil was wetted to a residual degree of saturation from being dry.
    • Whole life cost performance of domestic rainwater harvesting systems in the United Kingdom

      Roebuck, R.M.; Oltean-Dumbrava, Crina; Tait, Simon J. (2011)
      Rainwater harvesting (RWH) can be used to reduce the demand for potable mains water. At the single-building scale, previous research has focused on water-saving potential, while financial assessment has either been omitted or considered in an ad hoc manner. This paper reports on the application of a more rigorous financial analysis of domestic RWH systems than had been conducted previously. Whole life costing was selected as the most appropriate financial assessment technique. A total of 3840 domestic system configurations were assessed at a daily time step, taking into account various stakeholder perspectives and future cost scenarios. In each case, it was found that harvesting rainwater was significantly less cost effective than relying solely on mains-only water. The domestic RWH systems generally resulted in financial losses approximately equal to their capital costs. Without significant financial support, domestic RWH is unlikely to be cost effective for all reasonably foreseeable scenarios.