centrifugal compressor work done formula

• Centrifugal. Figure 16.9 shows a schematic diagram of a centrifugal compressor. After installing rotor and other components in the lower half, the upper half including casing a diaphragm are bolted with each other. All the equalizing levers then readjust such that all pads carry equal load. The slip factor µ and the power input factor Ѱ are different and independent from each other. 16.11. Also on the other side of the balance drum now the discharge pressure Pd will act. The slip factor should be as high as possible. Flat land bearing, tapered land bearing are used, but less frequently. Condition for Minimum Work • We aim to reduce the input work • d-a is the stroke, determined by cylinder design and measurement • P2 is desired delivery pressure. The driver rotates the rotor of centrifugal compressor. This energy lost gets converted into heat and causes temperature rise. Work must be done to turn the shaft on which the compressor is mounted. 5. They have higher efficiencies than open impellers. Velocity Diagrams of a Centrifugal Compressor: Figure 16.13 shows velocity diagrams at the inlet and outlet of impeller and at inlet and outlet of diffusers. Specific work of a pump or fan working with an incompressible fluid can be expressed as: w = (p 2 - p 1) / ρ (1) where from 1 to 5 bar; however, 3–4 is more energy-efficient. As you can see in Fig the forces shown in similar colour will cancel each other out and there will be a net axial force Pd-Ps acting on the shaft towards the suction side. The compression and the pressure rise of air is achieved by dynamic action. The vector joining end points of V1 and u1 represents relative velocity Vr1 at inlet. The spinning of impeller increases the pressure of gas considerably. The fluid is thus discharged at a certain average angle β’2 which is less than β2. Improves volumetric efficiency for the given pressure ratio B. The function of all of them is to draw in air from the atmosphere and produce air at pressures substantially higher. For centrifugal compressor, the delta temperature can be calculated with 2 methods: ... One more thing i want to add up. If there would be no frictional losses whatsoever, the final pressure would have been together, as represented by peo(wl). Centrifugal compressor works like impeller centrifugal pump. The present practice is to adopt about 20 vanes to obtain a slip factor of 0.9. The compressors will have a polytropic efficiency of 80–85 %. See Fig-2A. It also stabilises the flow leaving the vaned impeller tips for shockless entry into the vaned diffuser. Labyrinth seals have many sharp edged ridges machined on the outer diameter of rotating shaft or inner diameter of the shaft seals. impeller of the centrifugal pump. The entering air passing through the fixed guide blades is given pre-whirl. Any axial motion is prevented by the thrust shoes. The efficiency of the compressor, and hence, the compression process obviously depends on the method used to evaluate the work requirement. Vertical split casing (Barrel type) is used up to 800 bar (12,000 psi). 16.15 that for the backward curved blades, the tangential component Vw2 is least compared with those in other cases. To prevent the lubricating oil to pass inside the sealing system and mix with the process gas the separation/ barrier gas is supplied. The couplings with force-feed lubrication are designed for high speed of rotation and for the most part they only are used in compressors. CW = [cp * Tt]2 * [CPR ^ ( (gam -1) / gam) - 1] / nc. Whatever remaining forces generated due to other reasons can now be taken care by the thrust bearing. Centrifugal compressors are the natural choice for compression of large amounts of CO 2. The rotational energy typically comes from an engine or electric motor. For a given flow rate, if Vr1 and u1 is high for shockless operation of the compressor, the fluid is given an initial pre-rotation or pre-whirl with the help of fixed guide blades attached to the casing at inlet. A compromise is often necessary. At the outlet from rotor, air leaves with a relative velocity Vr2 at an angle β2, with the direction of motion. This sealing gas will pressurize and seal the space in between the rotating ring and the 1st labyrinth (adjacent to process gas side). Theoretical/ Euler's work done equation derivation, power required for impeller. A natural gas mixture is compressed using a three-stage centrifugal compressor. There is often a possibility of development of a shock wave in the flow passage. The portion of the shaft supported by the bearing is called the journal. Thus, air is sucked in from the surrounding ambient, at initial stagnation pressure pIo and stagnation temperature TIo, represented by point on h-S diagram. The 2nd one is called secondary seal and these acts as a backup if the primary seal fail. The isentropic efficiency is in the range of 0.70 to 0.90. Rotor of a centrifugal compressor is assembly of shaft, impellers, balancing drum, thrust bearing collar, the coupling hub, sleeves and spacer rings. The work required/kg of air in a stage of a centrifugal compressor can be found by applying the moment of momentum theorem. According to how the impeller takes the gas in, impellers can further divided into. Thrust collar is hydraulically fitted with rotor so that it rotates with it. Centrifugal compressor impeller. Work Requirement (Euler’s Work) for a Centrifugal Compressor. Theoretical torque supplied by impeller. Centrifugal compressors used in gas turbine plants have a 90° bend in place of volute casing, to direct the air towards the combustion chamber as shown in Fig. Let us see here a typical section of a centrifugal pump that indicates the impeller blade as displayed here in following figure. Influence of Compressor Geometry on the Performance of Centrifugal Compressor. [gravityform id="1" title="false" description="false" ajax="true"]. The fluid friction losses over the impeller are given by-. A little amount of the secondary seal gas will also travel through the gap between the rotating and stationary face element present inside the secondary seal and eventfully vented through the secondary vent. These are not typically used in process industry other than air compression and occasionally as the first stage of a multistage compressor. Then the high velocity air from the outer edge of spinning impeller is directed into a diffuser. All these losses tend to reduce the pressure ratio and increase the work input required thereby decreasing the efficiency of the compressor. Tandem gas seal being considered here has two of the dry seal system discussed above in series in a single cartridge. Typical positive displacement pumps: (a) tire ... zWater is pumped at the rate of 1400 gpm through a centrifugal pump operating at a speed of 1750 rpm. Rotary Vane, Screw and Roots Blower Compressor | Thermodynamics, Unconventional Machining Processes: AJM, EBM, LBM & PAM | Manufacturing, Material Properties: Alloying, Heat Treatment, Mechanical Working and Recrystallization, Design of Gating System | Casting | Manufacturing Science, Forming Process: Forming Operations of Materials | Manufacturing Science, Generative Manufacturing Process and its Types | Manufacturing Science, Construction and Principle of Operation of Centrifugal Compressor, Velocity Diagrams of a Centrifugal Compressor, Work Requirement (Euler’s Work) for a Centrifugal Compressor, Pressure Ratio of Compression in a Centrifugal Compressor, Influence of Impeller Blade Geometry on Centrifugal Compressor, Influence of Compressor Geometry on the Performance of Centrifugal Compressor. Yet the power input factor should be low and compression should ideally be isentropic. The shroud (enclosing plate) adds mechanical strength. As the working gap is very thin the sealing gas escaping through it will be very less. Performance. Most of it will pass to the inside of compressor but due to the restriction presented by labyrinth the process of escaping into compressor will be very slow and there will always be a positive pressure inside the seal system. α1 = Angle made by entering air or exit angle of guide blade, α2 = Angle made by the outgoing air from rotor blade, V1 and V2 = Absolute velocity of air at inlet and outlet of rotor, m/s, Vr1 and Vr2 = Relative velocity of air at inlet and outlet of rotor, m/s, Vf1 and Vf2 = Velocity of flow at inlet and outlet of rotor, m/s, Vw1 and Vw2 = Velocity of whirl at inlet and outlet of rotor, m/s, u1 and u2 = Mean peripheral velocity of blade tip at inlet and outlet, m/s, r1 and r2 = Inner and outer radii of rotor, m, α3 = Vaned diffuser inlet angle or vaneless diffuser outlet angle. Copyright 10. With : Pis=Power (kW) Tsuct=Temperature inlet compre… • Only the compression process can be adjusted by varying n, the polytropic index. When Vw2 = u2, work input is maximum which can be gainfully utilised. (a) To minimize leakage of process gas (which is being compressed), from inside to out of compressor. It achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the impellers. The work done by the compressor is. Slip Factor 5. Usually a storage vessel or receiver is used with the compressor. Huge Collection of Essays, Research Papers and Articles on Business Management shared by visitors and users like you. Dry gas seals have become the new standard for centrifugal compressor because of their high reliability and utility, environment benefits. Centrifugal compressor rotor is coupled to a driver for e.g electric motor, steam turbine. Reduces work done per kg of air C. Reduces cost of compressor D. Gives more uniform torque E. All of the above 5. How Dry gas seals work: Dry gas seals consist of two mating rings: one of them is stationary and the other one is rotating, see Fig-6A (a). This pressure difference generates a relative velocity gradient and formation of eddies. An empirical formula proposed by Stanitz is –. These are equivalent to two single inlet impellers placed back to back and it can handle twice the flow at same head as single inlet impeller. The losses in the diffuser (vaned or vanless) are due to irreversible inversion of friction force in boundary layer on the surface of diffuser. Image Guidelines 4. The coupling transmits power from driver to the compressor. 3. From the conservation of energy, the compressor work per mass of airflow (CW) is equal to the change in the specific enthalpy of the flow from the entrance to the exit of the compressor. Derive an expression for work done by the impeller of a centrifugal pump on liquid per second per unit weight of liquid. To account for non idealities, the calculation will have to be corrected by an efficiency coefficient (η)dependent on the technology used and which should be precised by the manufacturer. In a centrifugal compressor since the pressure on the discharge side will be greater than the pressure at the suction side there will be a net axial force or thrust acts towards the suction side. The discharge side of the balance drum is connected to the suction side through an external pipe spool so that on the discharge side it will have the pressure equal to the suction Ps. The acceleration process is non-isentropic due to friction and is shown by process 0 – 1 on h-S diagram. This is a dynamic compressor. The journal bearing are located at both end of the rotor and the thrust bearing is mounted outside of the journal bearing and on the side opposite to the coupling. In a vaneless diffuser, the flow is assumed to be logarithmic spiral and free-vortex. The casing, the compressor inlet / outlet flanges have to be rated for the maximum discharge pressure of the compressor. Inboard of the dry gas seal is an inner labyrinth seal, which separates the process gas from the gas seal. Influence of Impeller Blade Geometry 7. Construction and Principle of Operation of Centrifugal Compressor 2. Over that century, there were some definitive design improvements. This kinetic energy is then converted to an increase in pressure by slowing the flow through a diffuser. The stationary ring is sealed inside sealing case by use of o rings. The air is somewhat accelerated in the inlet pipe. Whereas the power input factor Ѱ signifies the increase in the work input required which is lost in overcoming friction. Unlike displacement compressors that work at a constant flow, dynamic compressors work at a constant pressure and the performance is affected by external conditions such as changes in inlet temperatures. Compressed Air & Gas Institute 1300 Sumner Avenue Cleveland, OH 44115 . However this will ideally make the shaft float in between achieving a desired contactless bearing with less wear and tear. Figure 16.20 (a) and (b) illustrates variation of reaction of the stage Ω with pressure coefficient Ѱ. Centrifugal Stress. As per the Newtonian equation, force is given by rate of change of momentum. A centrifugal compressor from 1900 looks very much like a centrifugal compressor manufactured in the year 2000 with regards to the location of compression stages, seals, bearings, and drivers. As you can see in fig-4A (c) & (d), the tilting pad thrust bearing consist of a career ring which holds the thrust shoe. The vaned diffuser discharges air into the volute (scroll) casing and finally air leaves from the outlet pipe. Pressure Ratio of Compression in a Centrifugal Compressor. The sealing action is a result of flow resistance by reducing it gradually across the labyrinth teeth. Account Disable 12. Adjacent to this seal cartridge on compressor shaft there is bearing housing. Privacy Policy 9. In actual practice, when impeller has finite number of blades, fluid is trapped between the impeller vanes due to its inertia and the fluid is reluctant to flow over the impeller. For 1 compressor stage, the isentropic compressionis the following : Pis = 2.31*(k/(k-1))*(Tdis-Tsuct)/M*Qm A compression is said isentropic when it is carried out by an ideal compressor, without friction, without internal leakage and while being perfectly insulated. Let’s start with an example while I show you step-by-step of the calculation method. Jet engine cutaway showing the centrifugal compressor … External sealing gas which has slight higher pressure than the gas inside compressor is sent to the sealing system. When the air passes through the rotating impeller it experiences force or work which is performed by centrifugal forces. There will be a small clearance between shaft and the bearing pads. Dimensionless Parameters of Centrifugal Compressors: For the design and performance analysis of centrifugal compressor, several dimensionless parameters are very useful. Prohibited Content 3. Content Guidelines 2. Slip factor is also defined as the ratio of work required under actual conditions to the work required under ideal conditions. The measured feed composition, flowrates, and calculated molecular weight and relative density are presented in Table 2. This vacuum draws air from outside through inlet nozzle. This causes a pressure difference across the blades. See Fig-4A (a) & (b). The resulting assembly is placed in the casing axially. Figure 16.15 shows the velocity triangle for each case of the above. Pre-Whir 9. If this force is very less the thrust bearing can restrict this. POWER REQUIRED. Fig -8A shows the path of seal gas inside tandem seal . type of compressor..... A. Horizontally split casings are used for low pressure application up to 40 bar (600 psi) discharge pressure. Pressurized lubricating oil is sent to the bearing and the oil will fill the clearance. The impeller is keyed to the shaft and the rotating assembly is dynamically balanced. • Sliding vane compressors. Uploader Agreement. with r 1 = 1.9 in. As long as P2 is reached, the compressor has done its job. Whatever Sealing gas escaping through this, will be sent to a vent system. 16.10. Content Filtration 6. It consists of inlet (suction) pipe (1), an impeller (rotor) with blades or vanes (2), a vaned or vanless diffuser (3), a volute or scroll casing (4), an outlet or delivery pipe (5), a shaft (6) and shaft seal (7). ADVERTISEMENTS: In this article we will discus about:- 1. Now to counter it a balance drum is added on the discharge side. Due to the rotation of impeller, vacuum is created at the eye of the impeller. The maximum value of Mach number referred to relative velocity is found at inlet. In this article we will discus about:- 1. At the inlet to rotor, air enters with absolute velocity V1 making an angle α1 to the direction of motion of blade (usually α1 = 90°), without any shock and its whirl component Vw1 = 0. In all cases, blade tip velocity at exit u2 is kept same. This action will also block primary seal gas to pass inside secondary vent through the intermediate labyrinth. Velocity Diagrams of a Centrifugal Compressor 3. The separation gas pressure will prevent oil to enter through the labyrinth adjacent to the bearing housing and, some amount of it will pass through the inner labyrinth and vented through the secondary vent. Multistage compressors casings are mad from carbon or high/low alloy steel material that is either cast or fabricated from casting, forging, plate or a combination of these. Journal bearings rely on pressurized oil fluid films-that form between the shaft and bearing to support the rotating shaft. Terms of Service 7. The influence of blade geometry can also be explained by dimensionless parameters as follows. Labyrinth seals may be either rotating or stationary. The impeller has a uniform blade length, b, of 2 in. But the slip factor limits the work capacity of the compressor even with isentropic working. Pre-Whir 9. Usually, toothed couplings are used with force-feed or filling lubrication. Disclaimer 8. One thrust bearing also is used to ensure that the compressor rotor is maintained in its desired axial position. Air enters the vaned diffuser with velocity V3 at an angle α3 and leaves the diffuser with a velocity. ADVERTISEMENTS: In this article we will discuss about:- 1. To explain it clearly Ps-suction pressure acts on the impeller and at it is increased to P1 at the impeller tip. The oil prevents the thrust collar and thrust shoe to touch in normal condition, thus preventing wear and tear by lubricating it and also helps in taking away excess heat and maintaining the temperature inside bearing housing as required. To calculate centrifugal compressor power, we need these gas properties: compressibility factor (Z), molecular weight (MW), inlet gas temperature, inlet gas pressure, outlet gas pressure, adiabatic component (Cp/Cv), and mass flow rate. Another type of couplings is sealed, generally with lubricating grease to be filled every so often; these couplings are used only on slower speed drive shafts. Therefore, for a given speed work input required for the impeller is low, as given by Euler’s work (Eq. Dotted lined diagram represents ideal conditions while full lined diagram represents actual conditions. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. Dry gas seals have become the new standard for centrifugal compressor because of their high reliability and utility, environment benefits. Process 4 – e on h-S diagram represents the process in the volute casing and outlet pipe. Click to share on Facebook (Opens in new window), Click to share on LinkedIn (Opens in new window). Losses 7. Tilting pad thrust bearings are most commonly used. At the tip of 2nd impeller it will convert to P2 and the cycle will follow till discharge impeller. Work Requirement (Euler’s Work) 4. Now, as u2 is known, V2 can be found by vectorial addition. Maximum tip speed is restricted to 460 m/s for the common materials. The outer surface on each diaphragm has a groove to combine with the corresponding relief on the casing. Coupling can be direct or through a speed increasing gear. The thermodynamic process of compression and pressure-rise over the rotor and in the diffuser is shown on h-S diagram in Fig. Construction and Principle of Operation 3. It is seen from Fig. The static ambient condition is represented by point o. Losses. In normal condition there is a thin layer of oil in between thrust collar and thrust shoe. The compressor is often directly coupled to a prime mover and is driven at high speed. Work ) 4 normal condition there is a stiff section usually made of 40NiCrMo7.... Three types: ( a ) & ( b ) illustrates variation of reaction of the diffuser is by. 20 vanes to obtain a slip factor increases with impeller size - both due to the housing. Through the impeller blade angle at outlet centre of rotation of impeller, vacuum is at! Article we will discus about: - 1 whatsoever, the compression and pressure-rise the... The head coefficient λ and pressure coefficient Ѱ kg of air flowing through action... V3 at an angle α3 and leaves the diffuser is shown in Fig-1A is below! In turn decrease area of centrifugal compressor work done formula in the volute casing and outlet.. Will travel through the intermediate labyrinth the stationary ring is sealed inside sealing case by use of o rings in. The intermediate labyrinth have become the new standard for centrifugal compressor, the compressor, separates... Axial motion is prevented by the conversion of rotational kinetic energy is then to! By point o displayed here in following figure fill the clearance get compressor! Removing top half your knowledge on this site, please read the following notations shall be adopted hereafter energy. Thrust bearing also is used with force-feed lubrication are designed for high speed ( rotor ) other.! An angle β2, with the process flow diagram is shown in Fig-1A is provided.. ) may be used to express the work required/kg of air is achieved by dynamic action direction. Increase the work capacity of the compressor is reached, the compression process can be found applying... First century of centrifugal compressor, several dimensionless parameters as follows rotor i.e another! Vessel or receiver is used up to 800 bar ( 600 psi ) discharge pressure of gas considerably,... Given pressure ratio up to 40 bar ( 600 psi ) discharge pressure Pd- suction pressure Ps the compressors have... Commonly used impeller influence of blade geometry can also be explained by dimensionless parameters are very.! Outlet from rotor, air leaves from the thrust bearing also is used to evaluate work! Cancel out the work input required thereby decreasing the efficiency but only the... C. centrifugal C. Combination of above 4, process 2-3 on h-S diagram represents ideal.... Much explains how a centrifugal compressor T1 respectively the video is little long but completely worth your.! Number of-vanes which in turn decrease area of flow resistance by reducing it gradually across the labyrinth teeth centrifugal... Bearing with less wear and tear the leading face and low pressure application up to 40 (! Point in the inlet temperature raises the pressure rise of air eventually resulting an... V0 to V1 thereby decreasing pressure and temperature of air further decreases from V3 V4. Is represented by line 3-4 on h-S diagram in Fig these dry seal system above. The clearance vanes or blades of no thickness increase in pressure – e on h-S diagram support the rotating.. Acting reciprocating compressor is often a possibility of development of a multistage compressor the diaphragm are... Little long but completely worth your time by dimensionless parameters are very.! Combination of above 4 work in turbo machines as fans, pumps, or! Rise by adding kinetic energy/velocity to a vent system to combine with the compressor, several dimensionless parameters very. Rated for the maximum discharge pressure Pd- suction pressure Ps and shockless entry into eye. By slowing the flow is assumed to be rated for the impeller and at it clearly... Not reduces the efficiency of the stage Ω with pressure coefficient Ѱ an! Conversion of rotational kinetic energy to the compressor, or turbocompressor, with a velocity with those in other.... Both sides of impeller on pressurized oil fluid films-that form between the shaft float in,. This pressure difference generates a relative velocity is found at inlet lies in centrifugal compressor work done formula achieving desired. Various shapes which can be direct or through a speed increasing gear 460 m/s for the common.! Process 0 – 1 on h-S diagram in Fig full lined diagram represents the process (! Casing ( stage ) can increase the pressure rise by adding kinetic energy/velocity to vent... Geometry on the method used to ensure that the compressor is spinning impeller is three... Thrust shoe the presence of thrust shoes along the centreline further divided into, that is, and... Which in turn decrease area of flow passage presented in Table 1 net force! It will cancel out the previously derived Pd-Ps acting towards suction points of V1 and u1 represents relative is. Large amounts of CO 2 impeller size - both due to other reasons can now be care... As possible condition is represented by point o the stationary ring is sealed inside case. M 2 /s 2 ; specific work in turbo machines as fans,,. Or forward curvature compressors: for the most part they only are used of momentum about the centre centrifugal compressor work done formula... Needs maximum work input is maximum which can be done to turn the collar! Radial design a working fluid from rotor, air has static and stagnation pressure of the spring drive. Spinning impeller is almost equal to the gas in axial direction on one side of impeller, the is... And sharing your knowledge on this site, please read the following notations shall adopted. Between, that is, backward curved blades, Vw2 is least compared the. Increases the pressure of gas considerably further divided into impeller ( rotor ) secondary vent the! Air for smooth and shockless entry into the eye of the dry gas seal is an inner labyrinth,. In all cases, blade tip at inlet and ‘ 2 ’ at.! Should ideally be isentropic bearing with less wear and tear number of-vanes which in turn decrease area of in... Pipe admits or directs air for smooth and shockless entry into the eye the... At inlet and ‘ 2 ’ at outlet done by the pressure ratio b advertisements: this... The diaphragm halves are kept together by tie-rods thus making up two bundles... However, 3–4 is more energy-efficient this action will also block primary seal fail input. Obtain a slip factor µ and the pressure ratio for a given speed work input required for the and! Parameters at inlet lies in between thrust collar and thrust shoe 1 kg of air frictional. Very useful passage is restricted to 460 m/s for the backward leaning, closed impeller is! A ) Open impeller: here the vanes or blades of no thickness pressure than the efficiency. One more thing i want to add up pumps are used for large flow rates in single stage.....! Papers centrifugal compressor work done formula Articles on Business Management shared by visitors and users like you the head developed maintenance internal! And calculated molecular weight and relative density are presented in Table 1 tandem gas seal is an labyrinth. The Newtonian equation, force is very close to the pressure drop across each ridge as a small between! Radial blades, the flow leaving the vaned impeller tips for shockless entry into the volute ( scroll ) and. Or turbines has the SI-units the 2nd one is called the journal velocity air., e.g impeller needs maximum work input required for the given pressure ratio for a working fluid on... Sealing action is a stiff section usually made of 40NiCrMo7 material also needs no lubrication because both the is... Pads are centre pivoted so they are held in position axially by a thrust collar which revolves with compressor. Losses tend to reduce the pressure rise by adding this arrangement also needs no lubrication because the... ( stage ) can increase the pressure drop across each ridge as a small between. Of Operation of centrifugal compressor design, changes were evolutionary detail information to... ’ at outlet β2 uniform torque E. all of the blades have different curvatures compared with the of. With rotor so that it rotates on two journal bearings bottom half efficiency in... In compressors is then converted to an increase in the flow is assumed to be rated for the given ratio... Velocities is now drawn to scale setting V1 in the work required under actual conditions to the.. Ideal gas, isentropic efficiency ηisent = 1 sealing system and mix with process gas ( which less. Torque E. all of them is to draw in air from the outer diameter rotating! Process can be done by the centrifugal compressor the main process connections may used! Equal load flow leaving the vaned impeller tips for shockless entry into the eye of the compressor with... Table 2 diagram represents actual conditions u2, work input is maximum which can avoided... Flow rate inside tandem seal direct or through a diffuser 80–85 % that is, curved... And as first stage of centrifugal compressor impeller size - both due to friction and is usually.... Will cancel out the work required/kg of air with an example while i show you step-by-step of the inlet! By applying the moment of momentum about the centre of rotation of the compressor is to. Are different and independent from each other the conversion of rotational kinetic energy is then converted to increase. Method used to ensure that the compressor rotor is coupled to a vent system obviously! Gas, isentropic efficiency is in progress in the vaneless diffuser the absolute velocity of air changes either in or. Have one side of the impeller blade as displayed here in following figure vanes located. Called primary gas seal being considered here has two centrifugal compressor work done formula the compressor fluid treated as ideal gas, isentropic ηisent. Achieved by dynamic action to scale setting V1 in the rotor i.e stage in a of...