Investigation of novel deflector shapes for uncontrolled spillways
| dc.contributor.advisor | Bosman, Adèle | en_ZA |
| dc.contributor.advisor | Brink, Isobel | en_ZA |
| dc.contributor.author | Wright, Henry John | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. | en_ZA |
| dc.date.accessioned | 2024-02-27T19:06:04Z | en_ZA |
| dc.date.accessioned | 2024-04-26T12:02:43Z | en_ZA |
| dc.date.available | 2024-02-27T19:06:04Z | en_ZA |
| dc.date.available | 2024-04-26T12:02:43Z | en_ZA |
| dc.date.issued | 2024-02 | en_ZA |
| dc.description | Thesis (PhD)--Stellenbosch University, 2024. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: The hydraulics of stepped spillways are generally well understood, although numerous fundamental hydraulic aspects remain inadequately explored. Critical knowledge gaps persist, including aerated flow hydraulics, hydraulics of embankment flows, hydraulics of stepped spillways for steep gravity dams, environmental hydraulics as well as turbulent interactions between cavity flow and skimming flow. Notably, the elusive safe unit discharge limits for stepped spillways remain undefined, with conflicting findings in the literature. The majority of stepped spillways have been designed for a maximum unit discharge of 25 to 30m3/s/m due to the risk of cavitation damage. It has further been reported that the critical velocity of approximately 20 m/s for the inception of cavitation on stepped spillways is obtained at a unit discharge of 25 m3/s/m. Further research in the field revealed that a bottom aerator becomes imperative for discharges greater than 30m3/s/m. However, discrepancies persist, with other researchers suggesting that the safe unit discharge is lower, quoting 11.5 m3/s/m to 14 m3/s/m for step heights of 0.6 m to 1.2m, respectively. Therefore, the exact limits of stepped spillways remain unquantified when water flows on the downstream slope. In China, the Flared Gate Pier (FGP) has been used on stepped spillways, particularly the X-type and Y-type piers. These piers support the crest gates and have been customised to contract the flow rapidly into a high-velocity jet. These piers have been used at, amongst others, the Dachaoshan Dam, a 111 m high Roller Compacted Concrete (RCC) gravity dam, with a maximum unit discharge designed of 193m3/s/m. These piers redirect flow into high-velocity jets, achieving efficient energy dissipation without relying on the stepped spillway face. Although historically utilised exclusively with gated spillways, FGPs hold potential as deflector-type energy dissipaters and were used as the basis for the novel deflector investigations in this research. To date, a variety of aerators have been fitted to improve spillway performance. Other aeration methods, such as the use of Roberts splitters, rectangular protrusions and triangular protrusions have been proposed, with some of these designs being successfully implemented. However, research has noted that these methods yield only marginal increases in the safe unit discharge of stepped spillways. The main concern regarding stepped spillways is the cavitation risk during high discharges, with a critical cavitation parameter of 0.5 compared to 0.2 for smooth chutes. This limits the maximum allowable unit discharge. While cavitation pitting has not been reported on prototype spillways, the exact conditions under which cavitation on stepped spillways may occur remain uncertain. The current research investigated the feasibility of a novel deflector form aimed at increasing the safe discharge capacity of spillways by deflecting the flow away from the spillway slope. The research incorporated a comprehensive approach, comprising a series of numerical models to simulate the hydrodynamic environment as well as four physical models. Numerical model simulations were undertaken with FLOW-3D HYDRO® and ANSYS FLUENT® computational fluid dynamics (CFD) software to optimise the deflector geometries before being tested with a physical model. A 1:50 scale physical model was constructed to investigate the influence of different deflector shapes. The investigation spans a range of prototype unit discharges ranging from 50 to 200m3/s/m and evaluates factors such as water surface profiles created by the deflector and pressure distribution on the deflector. A regression analysis was performed on the collected physical model data to develop equations that predict the jet's inner and outer trajectory and jet breakup length. The proposed novel deflectors developed in this study proved to be effective at various flow rates when the flow trajectory and threshold pressures were considered. These deflectors could be used for dams higher than 150 m and unit discharges ranging between 100 and 200 m3/s/m. Further research is required to improve, amongst others, deflector geometries, to study variables and to undertake additional measurements to conform and improve the efficiency of the novel deflectors, using this research as a basis. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Die hidroulika van trapoorlope word oor die algemeen goed verstaan, alhoewel talle fundamentele hidrouliese aspekte steeds onvoldoende ondersoek is. Kritieke leemtes bestaan steeds, soos hidroulika van belugte vloei, hidroulika van vloei oor vuldamme, hidroulika van trapoorlope vir steil gravitasiedamme, omgewingshidroulika, asook turbulente interaksie tussen holtes. Dit is merkbaar dat die ontwykende veilige eenheidsdeurstromingslimiete vir hierdie oorlope steeds ongedefinieer is, met teenstrydige bevindinge in die literatuur. Die meerderheid trapoorlope is ontwerp vir ’n maksimum eenheidsdeurstroming van 25 tot 30 m3/s/m weens die risiko van kavitasieskade. Dit is voorts gerapporteer dat die kritieke snelheid van ongeveer 20 m/s vir die aanvang van kavitasievorming bereik word teen ’n eenheidsdeurstroming van 25 m3/s/m Verdere navorsing in hierdie veld het getoon dat ’n bodembelugter noodsaaklik raak vir eenheidsdeurstroming van hoër as 30 m3/s/m. Teenstrydighede bestaan egter steeds met ander navorsers, wat aan die hand doen dat die veilige eenheidsdeurstroming laer is, en syfers van 11.5 m3/s/m tot 14 m3/s/m vir traphoogtes van 0.6 m tot 1.2 m onderskeidelik aanhaal. Daarom bly die presiese limiete van trapoorlope ongekwantifiseer. In China is die Uitklok-sluispyler (Flared Gate Pier [FGP]) op trapoorlope gebruik, veral die tipe Xen Y-pylers. Hierdie pylers steun die kruinsluise, maar is aangepas om die vloei vinnig saam te pers in ’n hoësnelheidstraal. Hierdie pylers is onder andere gebruik by die Dachaoshan Dam, ’n rolbeton-gravitasiedam van 111 m hoog, met ’n maksimum eenheidsdeurstroming wat van 193 m3/s/m. Hierdie pylers herlei vloei na hoësnelheidstrale, wat doeltreffende energieverspreiding bewerkstellig sonder om op die trapoorloopvlak te steun. Alhoewel dit histories uitsluitlik vir sluisoorlope gebruik is, het FGP’s potensiaal as deflektortipe energieverspreiders. Tot op hede is ’n verskeidenheid belugters aangebring om die effektiwiteit van oorlope te verbeter. Navorsing oor die gebruik van belugters is wyd gepubliseer. Ander belugtingsmetodes, soos die gebruik van Robert-stroombrekers, reghoekige uitsteeksels en driehoekige uitsteeksels, is voorgestel, terwyl van hierdie ontwerpe suksesvol geïmplementeer is. Navorsing het egter aangeteken dat hierdie metodes slegs ’n marginale toename in die veilige eenheidsdeurstroming van trapoorlope gelewer het. Die primêre bekommernis oor trapoorlope is die kavitasierisiko tydens hoë eenheidsdeurstroming, met ’n kritieke parameter van 0.5 vergeleke met 0.2 vir gladde oorlope. Dit beperk weer die maksimum toelaatbare eenheidsdeurstroming. Al is avitasieskade nie by prototipe-oorlope aangemeld nie, bly dit onseker onder watter presiese omstandighede dit by trapoorlope kan voorkom. Die huidige navorsing het die uitvoerbaarheid van ’n nuwe deflektorvorm ondersoek wat daarop gemik is om die veilige deurstroming van oorlope te verhoog deur die vloei weg van die oorloophelling te deflekteer. Hierdie navorsing sluit ’n omvattende benadering in, wat bestaan uit ’n reeks numeriese modelle om die hidrodinamiese omgewing te simuleer, sowel as vier fisiese modelle. Die afsonderlike numeriese modelle is gesimuleer met gebruik van FLOW-3D HYDRO®- en ANSYS FLUENT®-sagteware vir berekeningsvloeistofdinamika (computational fluid dynamics [CFD]) om die deflektorgeometrie te optimaliseer, alvorens dit met ’n fisiese model getoets is. ’n Fisiese 1:50-skaalmodel is gebou om die invloed van verskillende deflektorvorme te ondersoek. Die ondersoek behels ’n reeks prototipe-eenheidsdeurstromings van 50 tot 200 m3/s/m en evalueer faktore soos wateroppervlakprofiele wat deur die deflektor geskep word en drukverspreiding op die deflektor. 'n Regressie-analise is op die versamelde fisiese modeldata uitgevoer om vergelykings te ontwikkel wat die binne- en buitenste trajek en straal-opbreeklengte voorspel. Die voorgestelde nuwe deflektors wat in hierdie studie ontwikkel is, blyk doeltreffend te wees teen verskeie deurstromings as die vloeibaan en drempeldruk in ag geneem is. Hierdie deflektors kan vir damme hoër as 150 m en eenheidsdeurstroming tussen 100 en 200 m3/s/m gebruik word. Verdere navorsing is nodig om, onder andere, deflektorgeometrie en studieveranderlikes te verbeter, en om bykomende opmetings te onderneem om die doeltreffendheid van die nuwe deflektors aan te pas en te verbeter, deur hierdie navorsing as grondslag te gebruik. | af_ZA |
| dc.description.version | Doctorate | en_ZA |
| dc.format.extent | xviii, 189 pages : illustrations. | en_ZA |
| dc.identifier.uri | https://scholar.sun.ac.za/handle/10019.1/130285 | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject.lcsh | Spillways | en_ZA |
| dc.subject.lcsh | Water -- Aeration | en_ZA |
| dc.subject.lcsh | Cavitation | en_ZA |
| dc.subject.lcsh | Dams -- Design and construction | en_ZA |
| dc.title | Investigation of novel deflector shapes for uncontrolled spillways | en_ZA |
| dc.type | Thesis | en_ZA |
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