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Baloni, Beena D. Copenhagen, Denmark. June 11—15, Future development of more efficient volute casing depends on improving understanding of the design and flow analysis of the volute casing. This paper reviews different aspects of design and flow behavior inside the volute casing. It describes advantages and disadvantages of the different designs, the relation between flow and geometry, the impact on the impeller and the flow behavior inside the volute.
[GAMBIT] drawning volute casing of centrifugal fan
The main purpose is to provide an insight into the flow structure that can be used later to improve the performance or remediate some problems. The use of CFD is also discussed for the flow domain.
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Baloni Beena D. This Site. Google Scholar. Channiwala S. Author Information Beena D. Paper No: GT, pp. Published Online: July 9, Views Icon Views.There are different types of impellers and different types of casings. The way that different types of impellers and casings are combined produces all of the different types of pumps.
Volutes are designed to capture the velocity of liquid as it enters the outermost diameter of an impeller and convert the velocity of the liquid into pressure. In the picture to the right, notice that the impeller is not located in the center of the volute. This is intentional. The portion of the volute that extends closest to the impeller is called the cutwater. You will notice, that starting from the cutwater and proceeding in a counter-clockwise fashion, the distance between the volute and the impeller increases gradually.
Fundamental Pump Components: Volutes, Casings, and Impellers
This has the effect of causing pressure to build within the volute as the distance increases. Once the point of greatest separation is reached — directly next to the cutwater moving in clockwise direction — the pressure is at its greatest, and water is forced out the casing when it encounters the cutwater.
What a cutwater is to a volute, vanes are to a diffuser. While volutes only have one or sometimes two points where the edge of the casing approaches the edge of the impeller in order to begin building pressure, diffusers often have many vanes.
Single and double volute casing
In the case of the assembly drawing shown the diffuser contains 10 vanes as compared the volute casing which only has one. Also, while an impeller is placed in the center of a volute, an impeller generally sits directly adjacent to a diffuser and pushes water into the diffuser vanes. The basic function of a diffuser is similar to that of a volute. Diffuser vanes are positioned such that they begin close to the outer edge of the impeller and then gradually extend away from the impeller periphery.
Specific speedalso referred to as Ns, describes the relationship between how much flow an impeller produces and how much head it generates. To understand this concept, an example is called for.
Impeller No. This impeller design generates very little pressure relative to the amount of flow generated. This impeller design generates a great deal of pressure relative to the amount of flow generates. Below is a commonly-available graph that shows this relationship and how it affects impeller design. As you can see, impellers with lower specific speeds low-flow but high-head designs have very tight clearances. On the other end of the spectrum, you see impellers with high specific speeds high-flow but low-head designs.
These impellers, which are commonly called propellers once we reach the axial-flow field, have increasingly large internal clearances until you reach the axial-flow field in which case the impellers are completely open with no impeller covering or shroud. Another way to classify impellers is according to the design.
This method of classification is not unrelated to specific speed, and the specific speed of the impeller plays a large role in determining the physical design of the impeller. One differentiation in impeller design is the use or lack of a shroud or covering. Impellers with a top and bottom shroud are said to be enclosed impellers. Impellers without any shroud at all are said to be open impellers.
There are also single-shroud impellers in some specialty pumps, such as vortex impellers in solids-handling pumps. Such designs only have a top shroud and the impeller vanes are completely open to the liquid being pumped. Impellers of the single-shroud variety are ideally suited for applications where a large number of solids that might clog a shrouded impeller are present.
However, single-shroud vortex impellers are much less efficient than enclosed impeller designs. All of the impellers shown in the specific speed table above are of the single-suction design.
This means that there is a single portion of the impeller that is designed to take in water. There are also impellers designed to take suction from both sides of the impeller. A drawing of this type of impeller can be seen below. A double-suction impeller is a more balanced design than a single suction impeller because the two-sided design of the impeller balances the axial thrust loads imposed on the impeller and transmitted through the shaft to the pump bearings.A pump casing is often referred to as a volute.
A volute is a spiral-like geometry with an increasing through-flow area, reducing the velocity of the fluid and increasing the static pressure. The fluid exiting the impeller is then diffused towards the casing discharge nozzle.
These volute casings come in two different types: single volute and double volute. Single Volute Casing In a single volute casing, the impeller discharges into one volute that wraps completely around the impeller. This type of casing features one cutwater that directs the flow of the liquid towards the discharge of the pump.
Double Volute Casing Double volute casings have two cutwaters located degrees apart from each other. Normally a double volute pump can be identified simply by looking down the discharge flange: a noticeable vane is located inside the nozzle that divides the inner diameter of the discharge nozzle.
The main advantage of a double volute over a single volute is the balancing of radial loads on the impeller, as the double cutwater construction leads to a more equal pressure distribution in the volute. Minimizing the radial load on the bearings over the full operating range can have a significant impact on the lifetime of a pump, since bearing failures are the second most common reason for pump failures. However, a double volute adds additional hydraulic resistance. In addition to single and double volute casings, another type of pump casing exists: the diffuser casing.
A volute is a spiral-like form such that as the liquid is discharged from the impeller into the volute casing, the volute areas increase at a rate proportional to the discharge of liquid from the impeller and a constant velocity exists around the periphery of the impeller.
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Some employees work from home, which can lead to a less rapid response. We hope for your understanding. Single and double volute casing Pump Casing The casing is the major stationary component of the pump and mainly provides two functions: Converting velocity head from the impeller into pressure head and guidance of the flow to the discharge connection Creating a pressure boundary for the pumped liquid A pump casing is often referred to as a volute.
Product information. A volute is a spiral-like form.
A volute is a spiral-like form such that as the liquid is discharged from the impeller into the volute casing, the volute areas increase at a rate proportional to the discharge of liquid from the impeller and a constant velocity exists around the periphery of the impeller Product information.
A selection from our range of volute products. More information.TURBOdesign Suite is a turbomachinery design software package for all types of turbomachinery, such as pumps, compressors, fans, turbines and torque converters, and based on a unique 3D Inverse Design approach. TURBOdesign Suite provides tools to designers to put them in direct control of aerodynamic design to streamline every step of the design process for turbomachinery components.
The code is applicable to all types of turbomachinery such as fans, pumps, compressors, turbines and torque converters in axial, mixed-flow and centrifugal configuration. TURBOdesign Optima is a fully integrated automatic optimization platform for the design of turbomachinery blades subject to multi-point and multi-objective design objectives. TURBOdesign Volute is a volute design code based on a 2D inverse design methodology which allows designers to account for circumferential variation of inlet flow angle and velocity so that off design conditions can be considered at the design stage.
TURBOdesign Shaper optimizes complex geometries with respect to given targets, such as total pressure loss and velocity uniformity. It does so by computing the sensitivities of the geometry itself versus those targets and then modifying it.
Powered by ANSYS SpaceClaim, it enables flexible geometry manipulation and exporting the generated models to a wide array of file formats, making it compatible with the most commonly used CAD software packages. Learn more about how global turbomachinery manufacturers use our products in their design system. Read our success stories from companies of all sizes who are transforming the way they design turbomachinery components.
TURBOdesign Volute allows for the specification of 2D velocity distributions at the inlet and iteratively calculates the shape of the volute outer wall for a user-specified cross-section that can either be symmetric or asymmetric.
This webinar will demonstrate how a centrifugal fan stage consisting of impeller and volute can be optimized for improved stage performance using the TURBOdesign Suite. This webinar will demonstrate a typical conventionally designed centrifugal pump stage consisting of impeller and volute can be optimized for improved stage performance by using the following modules of TURBOdesign Suite. TURBOdesign Volute introduces a novel approach to volute design for pumps which allows for more practical and faster volute design cycles, eliminating most of the traditional CAD volute design work.
A method aimed to reduce the development time of an automotive blower is investigated. The objectives are to improve the efficiency, to reduce the losses and flow unsteadiness. Wheel and volute performances are analyzed on an existing geometry, and results are used to specify targets for a 3D inverse design method. Search form Search. Our Technology. Our Technology TURBOdesign Suite is a turbomachinery design software package for all types of turbomachinery, such as pumps, compressors, fans, turbines and torque converters, and based on a unique 3D Inverse Design approach.
TURBOdesign 2. Knowledge Hub. Knowledge Hub Learn more about how global turbomachinery manufacturers use our products in their design system.A method is presented for redesigning a centrifugal impeller and its inlet duct. The double-discharge volute casing is a structural constraint and is maintained for its shape.
The redesign effort was geared towards meeting the design volute exit pressure while reducing the power required to operate the fan. Given the high performance of the baseline impeller, the redesign adopted a high-fidelity CFD-based computational approach capable of accounting for all aerodynamic losses. The present effort utilized a numerical optimization with experiential steering techniques to redesign the fan blades, inlet duct, and shroud of the impeller.
The resulting flow path modifications not only met the pressure requirement, but also reduced the fan power by 8. The calculations verified that the new impeller matches better with the original volute. Model-fan measured data was used to validate CFD predictions and impeller design goals. The CFD results further demonstrate a Reynolds-number effect between the model- and full-scale fans.
A heavy-duty air cushion vehicle usually employs centrifugal lift fans to pressurize the air cushion and power the steering thruster. The design of the lift fan system is subject to meet payload, machinery spacing, and ruggedness requirements [ 1 ]. The impeller is a double-width, double-inlet DWDI centrifugal type with two nonstaggered blade rows. Each impeller blade row has backward-swept blades mounted between a common back plate and shrouds. Since the DDV is a structural constraint and required to be maintained in its shape, the baseline impeller and a dual bellmouth or inlet duct assembly are therefore redesigned to improve the fan performance.
In addition to the baseline impeller, there is an existing reference impeller named the B 2 impeller which provides further performance comparisons in reference to the baseline. In this paper, a systematic numerical study was carried out of the aerodynamic characteristics of the existing impellers.
The study revealed that although the existing impellers were high performing to start with, there was some margin for improvement. In particular, both impellers were susceptible to flow separations near the leading edge of the blade and near the shroud region where the hub transitioned into the common backplate for the impeller system.
Subsequently, a piecemeal approach was taken in the redesign effort and the hub, shroud, and bellmouth as well as the impeller blades were redesigned to improve the performance of the fan system.
Experiential steering was used to alter the optimized two-dimensional blade profile into a three-dimensional swept blade that further enhanced the performance of the impeller.
A detailed study was also carried out of the coupled impeller-volute system. The interaction between the impeller and its associated volute can significantly alter the performance of the impeller. Several groups have reported their findings on the performance of impeller-volute systems. However, the majority of the prior related investigations in the literature dealt with centrifugal impellers and single discharge volutes.
For example, Kaupert and Staubli [ 2 ] recorded strong blade loading fluctuations as the blade passed the volute tongues on a double spiral volute, particularly at below design flow rates.
Hillewaert and Van den Braembussche [ 3 ] used numerical predictions of the 3D unsteady inviscid impeller flow interacting with the steady volute flow in centrifugal compressors at off-design conditions and found reasonable agreements with measurements. Lee and Bein [ 4 ] also applied steady CFD calculations to a centrifugal refrigerant compressor with an impeller, a vaneless diffuser, and a single discharge volute and obtained a good agreement in volute circumferential pressure with the measurements, particularly the pressure dip at the volute tongue.
Meakhail and Park [ 5 ], Atif et al. Although all three investigations [ 5 — 7 ] found that their prediction results agree with the measurements, Karanth and Sharma [ 7 ] revealed the presence of an optimum radial gap or the interacting region which could provide lower interaction losses. All these aforementioned studies mostly with a single discharge volute indicate a volute feedback to the impeller aerodynamics exists, particularly at the volute tongue location. The current DDV further complicates the flow pattern, shortens the pressure recovery path compared to the single discharge volute, and produces double pressure peaks at two peripheral tongue locations.
The significance of the feedback depends, however, on each individual design configuration. Without predefined knowledge of the volute feedback to the impeller performance, impellers from these past efforts [ 3 — 5 ] were designed without taking the volute feedback into consideration.
In our case, since we are primarily interested in performance of the lift fan system, we have catalogued the performance degradation with the addition of a hard-constrained volute. We have carried out the impeller-volute coupling calculations with the use of the frozen impeller approximation which provides a conservative estimate of the performance when compared to fully unsteady simulations.
Both fans with the existing impellers and the fan system with the redesigned impeller were tested to verify improvement in performance.A centrifugal pump works by converting the energy of a spinning impeller to increase the velocity of a liquid.
The impeller is the device that rotates in the liquid and is usually contained inside a volute, or casing. The impeller is typically connected to an electric motor which provides the energy to be transferred to the liquid. The pump must be designed to carry the desired flow rate, using the most efficient and properly sized motor. Determine the specific gravity of the liquid to be pumped. For water close to 65 degrees Fahrenheit and typical domestic sanitary sewage, the liquid is assumed to have a specific gravity of 1.
Determine the vertical distance from the center of the pump volute to the outlet of the discharge pipe. This is the lift of the pump and will be measured in feet. Determine if there is going to be any pressure at the discharge point. This pressure, measured in pounds per square inch PSImust be overcome by the pump in order to move the liquid. The pressure could be due to pressure in the pipe the discharge pipe is connected to, or it could be the pressure due to the discharge point being submerged in liquid.
If the pipe is submerged, the discharge pressure will be simply the maximum depth of submergence in feet. This is called the discharge pressure head. Note whether the discharge point is another pipe under pressure. If so, the discharge pressure head is converted to feet of head by dividing the pressure in PSI by the specific gravity of the liquid, then multiplying that answer bythen dividing again by This will give an answer in feet of head.
The total discharge head is the pump lift plus the discharge pressure head. Determine the head on the suction side of the pump. If the pump is drawing from a pipe under pressure, convert the pressure to feet of head.
Otherwise, the suction head is the distance from the free liquid level to the center of the pump volute. Subtract the suction head from the discharge head to determine the total Static Head of the pump. Determine the dynamic head by using the design flow of the pump.When designing a new compressor or pump, most of the focus is put on the impeller and diffuser because they are the elements that are responsible for the work input and its conversion from kinetic energy into static pressure.
However, they are not the only elements in a typical turbomachine stage. The volute can also play a significant, and sometimes dominant, role in stage performance. This blog will explore important factors in volute design. At the discharge of a radial turbomachine, the flow can be led to a tangential exit pipe, using a volute. The design of a successful volute involves several factors: inlet flow conditioning, proper volute sizing, throat placement and tongue configuration, and the exit conical diffuser layout.
A simple example of a volute with rotor separated by a short vaneless space. Designing for a volute does not begin with the volute, but rather with upstream elements.
A particular area of focus is how the flow comes onboard the volute. The flow must be prepared for the type of volute being used and conditioned appropriately.Centrifugal pump design
If the flow entering the volute is not prepared then volute effectiveness is already handicapped and performance will be sub-optimal. How you condition the flow to ensure volute success is dependent on the machine for which the volute is being designed.
If a vaneless diffuser is used before a volute, the diffuser usually includes some pinch to help condition the flow. The sizing of the volute scroll can also have a dramatic effect on the overall performance map of the pump or compressor. Volute scroll cross-sectional areas are defined on sections around the circumference of the volute, from 0 to degrees, with the tongue or cutwater at 0 degrees. At the compressor or pump design point, a volute is often designed to have little to no static pressure recovery in the scroll portion, through careful control of the circumferential section areas.
The sections are sized, using constant angular momentum, but can also be slightly increased in size around the circumference to account for boundary layer growth. If a volute is mismatched to a pump or compressor, the performance curve pressure rise or efficiency as a function of flow will be shifted to higher or lower flows. If the volute is undersized, the curve is shifted to lower flows. If oversized, the performance curve is shifted to higher flows. Sometimes this shift is done intentionally to fine-tune a machine to a desired flow range.
Scroll sections can have varying shapes with different impacts on performance, largely due to friction. Even though a circular volute cross section provides the smallest wall area per unit volume, in the end, the shape is most often dictated by installation geometric constraints. Compressor designers typically use overhung volutes, while commercial pump designers tend to favor a symmetric volute. Another critical aspect of volute design is the proper generation of the tongue or cutwater because the tongue shape can have a big impact on performance and range.
There are many factors that need to be considered, depending on the application. These factors can include manufacturing method and tolerances, material stresses, fluid erosion, tongue angle, offset from the upstream impeller, diffuser vane clocking, etc. There are also performance and range issues to consider. A well-designed tongue with small relative thickness may provide the lowest losses but may reduce operation range. A large radius tongue will provide a wider operating range, but may also incur increased design point losses.
Also critical to tongue design is the throat or minimum area the tongue generates. This area is what sets the capacity of the volute and is where the exit diffuser begins.
This can be a very difficult area to model in CAD with complex geometric shapes. Care must be taken that the resultant throat area is as intended or the volute will not perform as expected. It is also important that the tongue and throat geometry flow is such that the downstream volute exit diffuser will perform well. The final part of the volute that needs to be sized appropriately is the diffuser, from the volute throat to the mating pipe flange. There can be a sizable area ratio for this section, and a lot of performance can be lost in stalling this conical diffuser by not providing enough length for good diffusion.
Conical diffuser performance maps indicating expected pressure recovery for a given area ratio and length can be utilized for quick layout of this element.
At first, a volute appears to be rather simple and straightforward to layout, but designs should be checked by modeling if the volute design is outside tested experience from previous designs.